@@ -6618,18 +6618,6 @@
Force threading of all interrupt handlers except those
marked explicitly IRQF_NO_THREAD.
- threadprintk [KNL]
- Force threaded printing of all legacy consoles. Be
- aware that with this option, the shutdown, reboot, and
- panic messages may not be printed on the legacy
- consoles. Also, earlycon/earlyprintk printing will be
- delayed until a regular console or the kthread is
- available.
-
- Users can view /proc/consoles to see if their console
- driver is legacy or not. Non-legacy (NBCON) console
- drivers are already threaded and are shown with 'N'.
-
topology= [S390,EARLY]
Format: {off | on}
Specify if the kernel should make use of the cpu
@@ -3492,23 +3492,23 @@ void serial8250_console_write_thread(struct uart_8250_port *up,
*/
for (i = 0; i < len; i++) {
if (!nbcon_enter_unsafe(wctxt)) {
- nbcon_reacquire(wctxt);
+ nbcon_reacquire_nobuf(wctxt);
break;
}
uart_console_write(port, wctxt->outbuf + i, 1, serial8250_console_putchar);
if (!nbcon_exit_unsafe(wctxt)) {
- nbcon_reacquire(wctxt);
+ nbcon_reacquire_nobuf(wctxt);
break;
}
}
} else {
- nbcon_reacquire(wctxt);
+ nbcon_reacquire_nobuf(wctxt);
}
while (!nbcon_enter_unsafe(wctxt))
- nbcon_reacquire(wctxt);
+ nbcon_reacquire_nobuf(wctxt);
/* Finally, wait for transmitter to become empty and restore IER. */
wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
@@ -3567,13 +3567,8 @@ static ssize_t show_cons_active(struct device *dev,
for_each_console(c) {
if (!c->device)
continue;
- if (c->flags & CON_NBCON) {
- if (!c->write_atomic && !c->write_thread)
- continue;
- } else {
- if (!c->write)
- continue;
- }
+ if (!(c->flags & CON_NBCON) && !c->write)
+ continue;
if ((c->flags & CON_ENABLED) == 0)
continue;
cs[i++] = c;
@@ -28,7 +28,6 @@ static int show_console_dev(struct seq_file *m, void *v)
};
char flags[ARRAY_SIZE(con_flags) + 1];
struct console *con = v;
- char con_write = '-';
unsigned int a;
dev_t dev = 0;
@@ -59,14 +58,8 @@ static int show_console_dev(struct seq_file *m, void *v)
seq_setwidth(m, 21 - 1);
seq_printf(m, "%s%d", con->name, con->index);
seq_pad(m, ' ');
- if (con->flags & CON_NBCON) {
- if (con->write_atomic || con->write_thread)
- con_write = 'W';
- } else {
- if (con->write)
- con_write = 'W';
- }
- seq_printf(m, "%c%c%c (%s)", con->read ? 'R' : '-', con_write,
+ seq_printf(m, "%c%c%c (%s)", con->read ? 'R' : '-',
+ ((con->flags & CON_NBCON) || con->write) ? 'W' : '-',
con->unblank ? 'U' : '-', flags);
if (dev)
seq_printf(m, " %4d:%d", MAJOR(dev), MINOR(dev));
@@ -355,7 +355,7 @@ struct console {
/**
* @write_atomic:
*
- * NBCON callback to write out text in any context.
+ * NBCON callback to write out text in any context. (Optional)
*
* This callback is called with the console already acquired. However,
* a higher priority context is allowed to take it over by default.
@@ -373,8 +373,8 @@ struct console {
* The callback should allow the takeover whenever it is safe. It
* increases the chance to see messages when the system is in trouble.
* If the driver must reacquire ownership in order to finalize or
- * revert hardware changes, nbcon_reacquire() can be used. However,
- * on reacquire the buffer content is no longer available. A
+ * revert hardware changes, nbcon_reacquire_nobuf() can be used.
+ * However, on reacquire the buffer content is no longer available. A
* reacquire cannot be used to resume printing.
*
* The callback can be called from any context (including NMI).
@@ -388,19 +388,29 @@ struct console {
*
* NBCON callback to write out text in task context.
*
- * This callback is called after device_lock() and with the nbcon
- * console acquired. Any necessary driver synchronization should have
- * been performed by the device_lock() callback.
+ * This callback must be called only in task context with both
+ * device_lock() and the nbcon console acquired with
+ * NBCON_PRIO_NORMAL.
*
- * This callback is always called from task context but with migration
- * disabled.
+ * The same rules for console ownership verification and unsafe
+ * sections handling applies as with write_atomic().
*
- * The same criteria for console ownership verification and unsafe
- * sections applies as with write_atomic(). The difference between
- * this callback and write_atomic() is that this callback is used
- * during normal operation and is always called from task context.
- * This allows drivers to operate in their own locking context for
- * synchronizing output to the hardware.
+ * The console ownership handling is necessary for synchronization
+ * against write_atomic() which is synchronized only via the context.
+ *
+ * The device_lock() provides the primary serialization for operations
+ * on the device. It might be as relaxed (mutex)[*] or as tight
+ * (disabled preemption and interrupts) as needed. It allows
+ * the kthread to operate in the least restrictive mode[**].
+ *
+ * [*] Standalone nbcon_context_try_acquire() is not safe with
+ * the preemption enabled, see nbcon_owner_matches(). But it
+ * can be safe when always called in the preemptive context
+ * under the device_lock().
+ *
+ * [**] The device_lock() makes sure that nbcon_context_try_acquire()
+ * would never need to spin which is important especially with
+ * PREEMPT_RT.
*/
void (*write_thread)(struct console *con, struct nbcon_write_context *wctxt);
@@ -591,19 +601,17 @@ static inline bool console_is_registered(const struct console *con)
#ifdef CONFIG_PRINTK
extern void nbcon_cpu_emergency_enter(void);
extern void nbcon_cpu_emergency_exit(void);
-extern void nbcon_cpu_emergency_flush(void);
extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt);
extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt);
extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt);
-extern void nbcon_reacquire(struct nbcon_write_context *wctxt);
+extern void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt);
#else
static inline void nbcon_cpu_emergency_enter(void) { }
static inline void nbcon_cpu_emergency_exit(void) { }
-static inline void nbcon_cpu_emergency_flush(void) { }
static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; }
static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; }
static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; }
-static inline void nbcon_reacquire(struct nbcon_write_context *wctxt) { }
+static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { }
#endif
extern int console_set_on_cmdline;
@@ -283,7 +283,6 @@ static inline void dump_stack(void)
static inline void printk_trigger_flush(void)
{
}
-
static inline void console_try_replay_all(void)
{
}
@@ -6703,7 +6703,6 @@ void debug_show_all_locks(void)
if (!p->lockdep_depth)
continue;
lockdep_print_held_locks(p);
- nbcon_cpu_emergency_flush();
touch_nmi_watchdog();
touch_all_softlockup_watchdogs();
}
@@ -3,7 +3,6 @@
* internal.h - printk internal definitions
*/
#include <linux/console.h>
-#include <linux/jump_label.h>
#include <linux/percpu.h>
#include <linux/types.h>
@@ -22,11 +21,17 @@ int devkmsg_sysctl_set_loglvl(const struct ctl_table *table, int write,
(con->flags & CON_BOOT) ? "boot" : "", \
con->name, con->index, ##__VA_ARGS__)
+/*
+ * Identify if legacy printing is forced in a dedicated kthread. If
+ * true, all printing via console lock occurs within a dedicated
+ * legacy printer thread. The only exception is on panic, after the
+ * nbcon consoles have had their chance to print the panic messages
+ * first.
+ */
#ifdef CONFIG_PREEMPT_RT
-# define force_printkthreads() (true)
+# define force_legacy_kthread() (true)
#else
-DECLARE_STATIC_KEY_FALSE(force_printkthreads_key);
-# define force_printkthreads() (static_branch_unlikely(&force_printkthreads_key))
+# define force_legacy_kthread() (false)
#endif
#ifdef CONFIG_PRINTK
@@ -56,7 +61,7 @@ struct printk_ringbuffer;
struct dev_printk_info;
extern struct printk_ringbuffer *prb;
-extern bool printk_threads_enabled;
+extern bool printk_kthreads_running;
__printf(4, 0)
int vprintk_store(int facility, int level,
@@ -84,8 +89,7 @@ bool printk_percpu_data_ready(void);
} while (0)
void defer_console_output(void);
-
-bool is_printk_deferred(void);
+bool is_printk_legacy_deferred(void);
u16 printk_parse_prefix(const char *text, int *level,
enum printk_info_flags *flags);
@@ -95,15 +99,14 @@ int console_lock_spinning_disable_and_check(int cookie);
u64 nbcon_seq_read(struct console *con);
void nbcon_seq_force(struct console *con, u64 seq);
bool nbcon_alloc(struct console *con);
-void nbcon_init(struct console *con, u64 init_seq);
void nbcon_free(struct console *con);
enum nbcon_prio nbcon_get_default_prio(void);
void nbcon_atomic_flush_pending(void);
bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
int cookie, bool use_atomic);
-void nbcon_kthread_create(struct console *con);
-void nbcon_wake_threads(void);
-void nbcon_legacy_kthread_create(void);
+bool nbcon_kthread_create(struct console *con);
+void nbcon_kthread_stop(struct console *con);
+void nbcon_kthreads_wake(void);
/*
* Check if the given console is currently capable and allowed to print
@@ -120,13 +123,16 @@ static inline bool console_is_usable(struct console *con, short flags, bool use_
return false;
if (flags & CON_NBCON) {
- if (use_atomic) {
- if (!con->write_atomic)
- return false;
- } else {
- if (!con->write_thread)
- return false;
- }
+ /* The write_atomic() callback is optional. */
+ if (use_atomic && !con->write_atomic)
+ return false;
+
+ /*
+ * For the !use_atomic case, @printk_kthreads_running is not
+ * checked because the write_thread() callback is also used
+ * via the legacy loop when the printer threads are not
+ * available.
+ */
} else {
if (!con->write)
return false;
@@ -144,8 +150,8 @@ static inline bool console_is_usable(struct console *con, short flags, bool use_
}
/**
- * nbcon_kthread_wake - Wake up a printk thread
- * @con: Console to operate on
+ * nbcon_kthread_wake - Wake up a console printing thread
+ * @con: Console to operate on
*/
static inline void nbcon_kthread_wake(struct console *con)
{
@@ -169,9 +175,7 @@ static inline void nbcon_kthread_wake(struct console *con)
#define PRINTK_MESSAGE_MAX 0
#define PRINTKRB_RECORD_MAX 0
-static inline void nbcon_kthread_wake(struct console *con) { }
-static inline void nbcon_kthread_create(struct console *con) { }
-#define printk_threads_enabled (false)
+#define printk_kthreads_running (false)
/*
* In !PRINTK builds we still export console_sem
@@ -182,15 +186,18 @@ static inline void nbcon_kthread_create(struct console *con) { }
#define printk_safe_exit_irqrestore(flags) local_irq_restore(flags)
static inline bool printk_percpu_data_ready(void) { return false; }
+static inline void defer_console_output(void) { }
+static inline bool is_printk_legacy_deferred(void) { return false; }
static inline u64 nbcon_seq_read(struct console *con) { return 0; }
static inline void nbcon_seq_force(struct console *con, u64 seq) { }
static inline bool nbcon_alloc(struct console *con) { return false; }
-static inline void nbcon_init(struct console *con, u64 init_seq) { }
static inline void nbcon_free(struct console *con) { }
static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; }
static inline void nbcon_atomic_flush_pending(void) { }
static inline bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
int cookie, bool use_atomic) { return false; }
+static inline void nbcon_kthread_wake(struct console *con) { }
+static inline void nbcon_kthreads_wake(void) { }
static inline bool console_is_usable(struct console *con, short flags,
bool use_atomic) { return false; }
@@ -198,15 +205,99 @@ static inline bool console_is_usable(struct console *con, short flags,
#endif /* CONFIG_PRINTK */
extern bool have_boot_console;
+extern bool have_nbcon_console;
extern bool have_legacy_console;
+extern bool legacy_allow_panic_sync;
+
+/**
+ * struct console_flush_type - Define available console flush methods
+ * @nbcon_atomic: Flush directly using nbcon_atomic() callback
+ * @nbcon_offload: Offload flush to printer thread
+ * @legacy_direct: Call the legacy loop in this context
+ * @legacy_offload: Offload the legacy loop into IRQ or legacy thread
+ *
+ * Note that the legacy loop also flushes the nbcon consoles.
+ */
+struct console_flush_type {
+ bool nbcon_atomic;
+ bool nbcon_offload;
+ bool legacy_direct;
+ bool legacy_offload;
+};
/*
- * Specifies if the console lock/unlock dance is needed for console
- * printing. If @have_boot_console is true, the nbcon consoles will
- * be printed serially along with the legacy consoles because nbcon
- * consoles cannot print simultaneously with boot consoles.
+ * Identify which console flushing methods should be used in the context of
+ * the caller.
*/
-#define printing_via_unlock (have_legacy_console || have_boot_console)
+static inline void printk_get_console_flush_type(struct console_flush_type *ft)
+{
+ memset(ft, 0, sizeof(*ft));
+
+ switch (nbcon_get_default_prio()) {
+ case NBCON_PRIO_NORMAL:
+ if (have_nbcon_console && !have_boot_console) {
+ if (printk_kthreads_running)
+ ft->nbcon_offload = true;
+ else
+ ft->nbcon_atomic = true;
+ }
+
+ /* Legacy consoles are flushed directly when possible. */
+ if (have_legacy_console || have_boot_console) {
+ if (!is_printk_legacy_deferred())
+ ft->legacy_direct = true;
+ else
+ ft->legacy_offload = true;
+ }
+ break;
+
+ case NBCON_PRIO_EMERGENCY:
+ if (have_nbcon_console && !have_boot_console)
+ ft->nbcon_atomic = true;
+
+ /* Legacy consoles are flushed directly when possible. */
+ if (have_legacy_console || have_boot_console) {
+ if (!is_printk_legacy_deferred())
+ ft->legacy_direct = true;
+ else
+ ft->legacy_offload = true;
+ }
+ break;
+
+ case NBCON_PRIO_PANIC:
+ /*
+ * In panic, the nbcon consoles will directly print. But
+ * only allowed if there are no boot consoles.
+ */
+ if (have_nbcon_console && !have_boot_console)
+ ft->nbcon_atomic = true;
+
+ if (have_legacy_console || have_boot_console) {
+ /*
+ * This is the same decision as NBCON_PRIO_NORMAL
+ * except that offloading never occurs in panic.
+ *
+ * Note that console_flush_on_panic() will flush
+ * legacy consoles anyway, even if unsafe.
+ */
+ if (!is_printk_legacy_deferred())
+ ft->legacy_direct = true;
+
+ /*
+ * In panic, if nbcon atomic printing occurs,
+ * the legacy consoles must remain silent until
+ * explicitly allowed.
+ */
+ if (ft->nbcon_atomic && !legacy_allow_panic_sync)
+ ft->legacy_direct = false;
+ }
+ break;
+
+ default:
+ WARN_ON_ONCE(1);
+ break;
+ }
+}
extern struct printk_buffers printk_shared_pbufs;
@@ -18,7 +18,6 @@
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/string.h>
-#include <linux/syscore_ops.h>
#include <linux/types.h>
#include "internal.h"
#include "printk_ringbuffer.h"
@@ -213,8 +212,6 @@ static void nbcon_seq_try_update(struct nbcon_context *ctxt, u64 new_seq)
}
}
-bool printk_threads_enabled __ro_after_init;
-
/**
* nbcon_context_try_acquire_direct - Try to acquire directly
* @ctxt: The context of the caller
@@ -245,6 +242,13 @@ static int nbcon_context_try_acquire_direct(struct nbcon_context *ctxt,
struct nbcon_state new;
do {
+ /*
+ * Panic does not imply that the console is owned. However, it
+ * is critical that non-panic CPUs during panic are unable to
+ * acquire ownership in order to satisfy the assumptions of
+ * nbcon_waiter_matches(). In particular, the assumption that
+ * lower priorities are ignored during panic.
+ */
if (other_cpu_in_panic())
return -EPERM;
@@ -276,18 +280,29 @@ static bool nbcon_waiter_matches(struct nbcon_state *cur, int expected_prio)
/*
* The request context is well defined by the @req_prio because:
*
- * - Only a context with a higher priority can take over the request.
+ * - Only a context with a priority higher than the owner can become
+ * a waiter.
+ * - Only a context with a priority higher than the waiter can
+ * directly take over the request.
* - There are only three priorities.
* - Only one CPU is allowed to request PANIC priority.
* - Lower priorities are ignored during panic() until reboot.
*
* As a result, the following scenario is *not* possible:
*
- * 1. Another context with a higher priority directly takes ownership.
- * 2. The higher priority context releases the ownership.
- * 3. A lower priority context takes the ownership.
- * 4. Another context with the same priority as this context
+ * 1. This context is currently a waiter.
+ * 2. Another context with a higher priority than this context
+ * directly takes ownership.
+ * 3. The higher priority context releases the ownership.
+ * 4. Another lower priority context takes the ownership.
+ * 5. Another context with the same priority as this context
* creates a request and starts waiting.
+ *
+ * Event #1 implies this context is EMERGENCY.
+ * Event #2 implies the new context is PANIC.
+ * Event #3 occurs when panic() has flushed the console.
+ * Events #4 and #5 are not possible due to the other_cpu_in_panic()
+ * check in nbcon_context_try_acquire_direct().
*/
return (cur->req_prio == expected_prio);
@@ -595,11 +610,29 @@ static bool nbcon_owner_matches(struct nbcon_state *cur, int expected_cpu,
int expected_prio)
{
/*
- * Since consoles can only be acquired by higher priorities,
- * owning contexts are uniquely identified by @prio. However,
- * since contexts can unexpectedly lose ownership, it is
- * possible that later another owner appears with the same
- * priority. For this reason @cpu is also needed.
+ * A similar function, nbcon_waiter_matches(), only deals with
+ * EMERGENCY and PANIC priorities. However, this function must also
+ * deal with the NORMAL priority, which requires additional checks
+ * and constraints.
+ *
+ * For the case where preemption and interrupts are disabled, it is
+ * enough to also verify that the owning CPU has not changed.
+ *
+ * For the case where preemption or interrupts are enabled, an
+ * external synchronization method *must* be used. In particular,
+ * the driver-specific locking mechanism used in device_lock()
+ * (including disabling migration) should be used. It prevents
+ * scenarios such as:
+ *
+ * 1. [Task A] owns a context with NBCON_PRIO_NORMAL on [CPU X] and
+ * is scheduled out.
+ * 2. Another context takes over the lock with NBCON_PRIO_EMERGENCY
+ * and releases it.
+ * 3. [Task B] acquires a context with NBCON_PRIO_NORMAL on [CPU X]
+ * and is scheduled out.
+ * 4. [Task A] gets running on [CPU X] and sees that the console is
+ * still owned by a task on [CPU X] with NBON_PRIO_NORMAL. Thus
+ * [Task A] thinks it is the owner when it is not.
*/
if (cur->prio != expected_prio)
@@ -798,6 +831,19 @@ static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsaf
return nbcon_context_can_proceed(ctxt, &cur);
}
+static void nbcon_write_context_set_buf(struct nbcon_write_context *wctxt,
+ char *buf, unsigned int len)
+{
+ struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+ struct console *con = ctxt->console;
+ struct nbcon_state cur;
+
+ wctxt->outbuf = buf;
+ wctxt->len = len;
+ nbcon_state_read(con, &cur);
+ wctxt->unsafe_takeover = cur.unsafe_takeover;
+}
+
/**
* nbcon_enter_unsafe - Enter an unsafe region in the driver
* @wctxt: The write context that was handed to the write function
@@ -813,8 +859,12 @@ static bool __nbcon_context_update_unsafe(struct nbcon_context *ctxt, bool unsaf
bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt)
{
struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+ bool is_owner;
- return nbcon_context_enter_unsafe(ctxt);
+ is_owner = nbcon_context_enter_unsafe(ctxt);
+ if (!is_owner)
+ nbcon_write_context_set_buf(wctxt, NULL, 0);
+ return is_owner;
}
EXPORT_SYMBOL_GPL(nbcon_enter_unsafe);
@@ -833,13 +883,18 @@ EXPORT_SYMBOL_GPL(nbcon_enter_unsafe);
bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt)
{
struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+ bool ret;
- return nbcon_context_exit_unsafe(ctxt);
+ ret = nbcon_context_exit_unsafe(ctxt);
+ if (!ret)
+ nbcon_write_context_set_buf(wctxt, NULL, 0);
+ return ret;
}
EXPORT_SYMBOL_GPL(nbcon_exit_unsafe);
/**
- * nbcon_reacquire - Reacquire a console after losing ownership while printing
+ * nbcon_reacquire_nobuf - Reacquire a console after losing ownership
+ * while printing
* @wctxt: The write context that was handed to the write callback
*
* Since ownership can be lost at any time due to handover or takeover, a
@@ -854,21 +909,16 @@ EXPORT_SYMBOL_GPL(nbcon_exit_unsafe);
* output buffer because that has been lost. This function cannot be used to
* resume printing.
*/
-void nbcon_reacquire(struct nbcon_write_context *wctxt)
+void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt)
{
struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
- struct console *con = ctxt->console;
- struct nbcon_state cur;
while (!nbcon_context_try_acquire(ctxt))
cpu_relax();
- wctxt->outbuf = NULL;
- wctxt->len = 0;
- nbcon_state_read(con, &cur);
- wctxt->unsafe_takeover = cur.unsafe_takeover;
+ nbcon_write_context_set_buf(wctxt, NULL, 0);
}
-EXPORT_SYMBOL_GPL(nbcon_reacquire);
+EXPORT_SYMBOL_GPL(nbcon_reacquire_nobuf);
/**
* nbcon_emit_next_record - Emit a record in the acquired context
@@ -900,6 +950,21 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt, bool use_a
unsigned long dropped;
unsigned long ulseq;
+ /*
+ * This function should never be called for consoles that have not
+ * implemented the necessary callback for writing: i.e. legacy
+ * consoles and, when atomic, nbcon consoles with no write_atomic().
+ * Handle it as if ownership was lost and try to continue.
+ *
+ * Note that for nbcon consoles the write_thread() callback is
+ * mandatory and was already checked in nbcon_alloc().
+ */
+ if (WARN_ON_ONCE((use_atomic && !con->write_atomic) ||
+ !(console_srcu_read_flags(con) & CON_NBCON))) {
+ nbcon_context_release(ctxt);
+ return false;
+ }
+
/*
* The printk buffers are filled within an unsafe section. This
* prevents NBCON_PRIO_NORMAL and NBCON_PRIO_EMERGENCY from
@@ -936,7 +1001,8 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt, bool use_a
/*
* Ensure this context is still the owner before trying to
* update @nbcon_prev_seq. Otherwise the value in @ulseq may
- * not be from the previous owner.
+ * not be from the previous owner and instead be some later
+ * value from the context that took over ownership.
*/
nbcon_state_read(con, &cur);
if (!nbcon_context_can_proceed(ctxt, &cur))
@@ -954,38 +1020,28 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt, bool use_a
goto update_con;
/* Initialize the write context for driver callbacks. */
- wctxt->outbuf = &pmsg.pbufs->outbuf[0];
- wctxt->len = pmsg.outbuf_len;
- nbcon_state_read(con, &cur);
- wctxt->unsafe_takeover = cur.unsafe_takeover;
+ nbcon_write_context_set_buf(wctxt, &pmsg.pbufs->outbuf[0], pmsg.outbuf_len);
- if (use_atomic &&
- con->write_atomic) {
+ if (use_atomic)
con->write_atomic(con, wctxt);
-
- } else if (!use_atomic &&
- con->write_thread) {
+ else
con->write_thread(con, wctxt);
- } else {
- /*
- * This function should never be called for legacy consoles.
- * Handle it as if ownership was lost and try to continue.
- */
- WARN_ON_ONCE(1);
- nbcon_context_release(ctxt);
- return false;
- }
-
if (!wctxt->outbuf) {
/*
- * Ownership was lost and reacquired by the driver.
- * Handle it as if ownership was lost.
+ * Ownership was lost and reacquired by the driver. Handle it
+ * as if ownership was lost.
*/
nbcon_context_release(ctxt);
return false;
}
+ /*
+ * Ownership may have been lost but _not_ reacquired by the driver.
+ * This case is detected and handled when entering unsafe to update
+ * dropped/seq values.
+ */
+
/*
* Since any dropped message was successfully output, reset the
* dropped count for the console.
@@ -1011,6 +1067,63 @@ static bool nbcon_emit_next_record(struct nbcon_write_context *wctxt, bool use_a
return nbcon_context_exit_unsafe(ctxt);
}
+/*
+ * nbcon_emit_one - Print one record for an nbcon console using the
+ * specified callback
+ * @wctxt: An initialized write context struct to use for this context
+ * @use_atomic: True if the write_atomic() callback is to be used
+ *
+ * Return: True, when a record has been printed and there are still
+ * pending records. The caller might want to continue flushing.
+ *
+ * False, when there is no pending record, or when the console
+ * context cannot be acquired, or the ownership has been lost.
+ * The caller should give up. Either the job is done, cannot be
+ * done, or will be handled by the owning context.
+ *
+ * This is an internal helper to handle the locking of the console before
+ * calling nbcon_emit_next_record().
+ */
+static bool nbcon_emit_one(struct nbcon_write_context *wctxt, bool use_atomic)
+{
+ struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+ struct console *con = ctxt->console;
+ unsigned long flags;
+ bool ret = false;
+
+ if (!use_atomic) {
+ con->device_lock(con, &flags);
+
+ /*
+ * Ensure this stays on the CPU to make handover and
+ * takeover possible.
+ */
+ cant_migrate();
+ }
+
+ if (!nbcon_context_try_acquire(ctxt))
+ goto out;
+
+ /*
+ * nbcon_emit_next_record() returns false when the console was
+ * handed over or taken over. In both cases the context is no
+ * longer valid.
+ *
+ * The higher priority printing context takes over responsibility
+ * to print the pending records.
+ */
+ if (!nbcon_emit_next_record(wctxt, use_atomic))
+ goto out;
+
+ nbcon_context_release(ctxt);
+
+ ret = ctxt->backlog;
+out:
+ if (!use_atomic)
+ con->device_unlock(con, flags);
+ return ret;
+}
+
/**
* nbcon_kthread_should_wakeup - Check whether a printer thread should wakeup
* @con: Console to operate on
@@ -1062,7 +1175,6 @@ static int nbcon_kthread_func(void *__console)
short con_flags;
bool backlog;
int cookie;
- int ret;
wait_for_event:
/*
@@ -1075,50 +1187,30 @@ static int nbcon_kthread_func(void *__console)
*
* This pairs with rcuwait_has_sleeper:A and nbcon_kthread_wake:A.
*/
- ret = rcuwait_wait_event(&con->rcuwait,
- nbcon_kthread_should_wakeup(con, ctxt),
- TASK_INTERRUPTIBLE); /* LMM(nbcon_kthread_func:A) */
-
- if (kthread_should_stop())
- return 0;
-
- /* Wait was interrupted by a spurious signal, go back to sleep. */
- if (ret)
- goto wait_for_event;
+ rcuwait_wait_event(&con->rcuwait,
+ nbcon_kthread_should_wakeup(con, ctxt),
+ TASK_INTERRUPTIBLE); /* LMM(nbcon_kthread_func:A) */
do {
+ if (kthread_should_stop())
+ return 0;
+
backlog = false;
+ /*
+ * Keep the srcu read lock around the entire operation so that
+ * synchronize_srcu() can guarantee that the kthread stopped
+ * or suspended printing.
+ */
cookie = console_srcu_read_lock();
con_flags = console_srcu_read_flags(con);
- if (console_is_usable(con, con_flags, false)) {
- unsigned long lock_flags;
-
- con->device_lock(con, &lock_flags);
-
- /*
- * Ensure this stays on the CPU to make handover and
- * takeover possible.
- */
- cant_migrate();
-
- if (nbcon_context_try_acquire(ctxt)) {
- /*
- * If the emit fails, this context is no
- * longer the owner.
- */
- if (nbcon_emit_next_record(&wctxt, false)) {
- nbcon_context_release(ctxt);
- backlog = ctxt->backlog;
- }
- }
-
- con->device_unlock(con, lock_flags);
- }
+ if (console_is_usable(con, con_flags, false))
+ backlog = nbcon_emit_one(&wctxt, false);
console_srcu_read_unlock(cookie);
+
cond_resched();
} while (backlog);
@@ -1127,7 +1219,7 @@ static int nbcon_kthread_func(void *__console)
}
/**
- * nbcon_irq_work - irq work to wake printk thread
+ * nbcon_irq_work - irq work to wake console printer thread
* @irq_work: The irq work to operate on
*/
static void nbcon_irq_work(struct irq_work *irq_work)
@@ -1139,9 +1231,6 @@ static void nbcon_irq_work(struct irq_work *irq_work)
static inline bool rcuwait_has_sleeper(struct rcuwait *w)
{
- bool has_sleeper;
-
- rcu_read_lock();
/*
* Guarantee any new records can be seen by tasks preparing to wait
* before this context checks if the rcuwait is empty.
@@ -1154,20 +1243,20 @@ static inline bool rcuwait_has_sleeper(struct rcuwait *w)
* This pairs with nbcon_kthread_func:A.
*/
smp_mb(); /* LMM(rcuwait_has_sleeper:A) */
- has_sleeper = !!rcu_dereference(w->task);
- rcu_read_unlock();
-
- return has_sleeper;
+ return rcuwait_active(w);
}
/**
- * nbcon_wake_threads - Wake up printing threads using irq_work
+ * nbcon_kthreads_wake - Wake up printing threads using irq_work
*/
-void nbcon_wake_threads(void)
+void nbcon_kthreads_wake(void)
{
struct console *con;
int cookie;
+ if (!printk_kthreads_running)
+ return;
+
cookie = console_srcu_read_lock();
for_each_console_srcu(con) {
/*
@@ -1175,12 +1264,63 @@ void nbcon_wake_threads(void)
* actively waiting. If not waiting, the thread will
* notice by itself that it has work to do.
*/
- if (con->kthread && rcuwait_has_sleeper(&con->rcuwait))
+ if (rcuwait_has_sleeper(&con->rcuwait))
irq_work_queue(&con->irq_work);
}
console_srcu_read_unlock(cookie);
}
+/*
+ * nbcon_kthread_stop - Stop a console printer thread
+ * @con: Console to operate on
+ */
+void nbcon_kthread_stop(struct console *con)
+{
+ lockdep_assert_console_list_lock_held();
+
+ if (!con->kthread)
+ return;
+
+ kthread_stop(con->kthread);
+ con->kthread = NULL;
+}
+
+/**
+ * nbcon_kthread_create - Create a console printer thread
+ * @con: Console to operate on
+ *
+ * Return: True if the kthread was started or already exists.
+ * Otherwise false and @con must not be registered.
+ *
+ * If @con was already registered, it must be unregistered before
+ * the global state variable @printk_kthreads_running can be set.
+ */
+bool nbcon_kthread_create(struct console *con)
+{
+ struct task_struct *kt;
+
+ lockdep_assert_console_list_lock_held();
+
+ if (con->kthread)
+ return true;
+
+ kt = kthread_run(nbcon_kthread_func, con, "pr/%s%d", con->name, con->index);
+ if (WARN_ON(IS_ERR(kt))) {
+ con_printk(KERN_ERR, con, "failed to start printing thread\n");
+ return false;
+ }
+
+ con->kthread = kt;
+
+ /*
+ * It is important that console printing threads are scheduled
+ * shortly after a printk call and with generous runtime budgets.
+ */
+ sched_set_normal(con->kthread, -20);
+
+ return true;
+}
+
/* Track the nbcon emergency nesting per CPU. */
static DEFINE_PER_CPU(unsigned int, nbcon_pcpu_emergency_nesting);
static unsigned int early_nbcon_pcpu_emergency_nesting __initdata;
@@ -1188,8 +1328,14 @@ static unsigned int early_nbcon_pcpu_emergency_nesting __initdata;
/**
* nbcon_get_cpu_emergency_nesting - Get the per CPU emergency nesting pointer
*
+ * Context: For reading, any context. For writing, any context which could
+ * not be migrated to another CPU.
* Return: Either a pointer to the per CPU emergency nesting counter of
* the current CPU or to the init data during early boot.
+ *
+ * The function is safe for reading per-CPU variables in any context because
+ * preemption is disabled if the current CPU is in the emergency state. See
+ * also nbcon_cpu_emergency_enter().
*/
static __ref unsigned int *nbcon_get_cpu_emergency_nesting(void)
{
@@ -1201,16 +1347,21 @@ static __ref unsigned int *nbcon_get_cpu_emergency_nesting(void)
if (!printk_percpu_data_ready())
return &early_nbcon_pcpu_emergency_nesting;
- return this_cpu_ptr(&nbcon_pcpu_emergency_nesting);
+ /* Open code this_cpu_ptr() without checking migration. */
+ return per_cpu_ptr(&nbcon_pcpu_emergency_nesting, raw_smp_processor_id());
}
/**
* nbcon_get_default_prio - The appropriate nbcon priority to use for nbcon
* printing on the current CPU
*
- * Context: Any context which could not be migrated to another CPU.
+ * Context: Any context.
* Return: The nbcon_prio to use for acquiring an nbcon console in this
* context for printing.
+ *
+ * The function is safe for reading per-CPU data in any context because
+ * preemption is disabled if the current CPU is in the emergency or panic
+ * state.
*/
enum nbcon_prio nbcon_get_default_prio(void)
{
@@ -1226,46 +1377,6 @@ enum nbcon_prio nbcon_get_default_prio(void)
return NBCON_PRIO_NORMAL;
}
-/*
- * nbcon_emit_one - Print one record for an nbcon console using the
- * specified callback
- * @wctxt: An initialized write context struct to use for this context
- * @use_atomic: True if the write_atomic() callback is to be used
- *
- * Return: True, when a record has been printed and there are still
- * pending records. The caller might want to continue flushing.
- *
- * False, when there is no pending record, or when the console
- * context cannot be acquired, or the ownership has been lost.
- * The caller should give up. Either the job is done, cannot be
- * done, or will be handled by the owning context.
- *
- * This is an internal helper to handle the locking of the console before
- * calling nbcon_emit_next_record().
- */
-static bool nbcon_emit_one(struct nbcon_write_context *wctxt, bool use_atomic)
-{
- struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
-
- if (!nbcon_context_try_acquire(ctxt))
- return false;
-
- /*
- * nbcon_emit_next_record() returns false when the console was
- * handed over or taken over. In both cases the context is no
- * longer valid.
- *
- * The higher priority printing context takes over responsibility
- * to print the pending records.
- */
- if (!nbcon_emit_next_record(wctxt, use_atomic))
- return false;
-
- nbcon_context_release(ctxt);
-
- return ctxt->backlog;
-}
-
/**
* nbcon_legacy_emit_next_record - Print one record for an nbcon console
* in legacy contexts
@@ -1275,7 +1386,13 @@ static bool nbcon_emit_one(struct nbcon_write_context *wctxt, bool use_atomic)
* both the console_lock and the SRCU read lock. Otherwise it
* is set to false.
* @cookie: The cookie from the SRCU read lock.
- * @use_atomic: True if the write_atomic() callback is to be used
+ * @use_atomic: Set true when called in an atomic or unknown context.
+ * It affects which nbcon callback will be used: write_atomic()
+ * or write_thread().
+ *
+ * When false, the write_thread() callback is used and would be
+ * called in a preemtible context unless disabled by the
+ * device_lock. The legacy handover is not allowed in this mode.
*
* Context: Any context except NMI.
* Return: True, when a record has been printed and there are still
@@ -1298,30 +1415,28 @@ bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
unsigned long flags;
bool progress;
- ctxt->console = con;
+ ctxt->console = con;
+ ctxt->prio = nbcon_get_default_prio();
if (use_atomic) {
- /* Use the same procedure as console_emit_next_record(). */
+ /*
+ * In an atomic or unknown context, use the same procedure as
+ * in console_emit_next_record(). It allows to handover.
+ */
printk_safe_enter_irqsave(flags);
console_lock_spinning_enable();
stop_critical_timings();
+ }
- ctxt->prio = nbcon_get_default_prio();
- progress = nbcon_emit_one(&wctxt, use_atomic);
+ progress = nbcon_emit_one(&wctxt, use_atomic);
+ if (use_atomic) {
start_critical_timings();
*handover = console_lock_spinning_disable_and_check(cookie);
printk_safe_exit_irqrestore(flags);
} else {
+ /* Non-atomic does not perform legacy spinning handovers. */
*handover = false;
-
- con->device_lock(con, &flags);
- cant_migrate();
-
- ctxt->prio = nbcon_get_default_prio();
- progress = nbcon_emit_one(&wctxt, use_atomic);
-
- con->device_unlock(con, flags);
}
return progress;
@@ -1402,6 +1517,7 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq,
static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq,
bool allow_unsafe_takeover)
{
+ struct console_flush_type ft;
unsigned long flags;
int err;
@@ -1434,7 +1550,8 @@ static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq,
* context must flush those remaining records if the printer thread
* is not available do it.
*/
- if ((!con->kthread || (system_state > SYSTEM_RUNNING)) &&
+ printk_get_console_flush_type(&ft);
+ if (!ft.nbcon_offload &&
prb_read_valid(prb, nbcon_seq_read(con), NULL)) {
stop_seq = prb_next_reserve_seq(prb);
goto again;
@@ -1475,8 +1592,9 @@ static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_takeove
* write_atomic() callback
*
* Flush the backlog up through the currently newest record. Any new
- * records added while flushing will not be flushed. This is to avoid
- * one CPU printing unbounded because other CPUs continue to add records.
+ * records added while flushing will not be flushed if there is another
+ * context available to handle the flushing. This is to avoid one CPU
+ * printing unbounded because other CPUs continue to add records.
*/
void nbcon_atomic_flush_pending(void)
{
@@ -1497,16 +1615,12 @@ void nbcon_atomic_flush_unsafe(void)
/**
* nbcon_cpu_emergency_enter - Enter an emergency section where printk()
- * messages for that CPU are only stored
- *
- * Upon exiting the emergency section, all stored messages are flushed.
+ * messages for that CPU are flushed directly
*
* Context: Any context. Disables preemption.
*
- * When within an emergency section, no printing occurs on that CPU. This
- * is to allow all emergency messages to be dumped into the ringbuffer before
- * flushing the ringbuffer. The actual printing occurs when exiting the
- * outermost emergency section.
+ * When within an emergency section, printk() calls will attempt to flush any
+ * pending messages in the ringbuffer.
*/
void nbcon_cpu_emergency_enter(void)
{
@@ -1519,178 +1633,52 @@ void nbcon_cpu_emergency_enter(void)
}
/**
- * nbcon_cpu_emergency_exit - Exit an emergency section and flush the
- * stored messages
+ * nbcon_cpu_emergency_exit - Exit an emergency section
*
- * Flushing only occurs when exiting all nesting for the CPU.
- *
- * Context: Any context. Enables preemption.
+ * Context: Within an emergency section. Enables preemption.
*/
void nbcon_cpu_emergency_exit(void)
{
unsigned int *cpu_emergency_nesting;
- bool do_trigger_flush = false;
cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting();
- /*
- * Flush the messages before enabling preemtion to see them ASAP.
- *
- * Reduce the risk of potential softlockup by using the
- * flush_pending() variant which ignores messages added later. It is
- * called before decrementing the counter so that the printing context
- * for the emergency messages is NBCON_PRIO_EMERGENCY.
- */
- if (*cpu_emergency_nesting == 1) {
- nbcon_atomic_flush_pending();
-
- /*
- * Safely attempt to flush the legacy consoles in this
- * context. Otherwise an irq_work context is triggered
- * to handle it.
- */
- do_trigger_flush = true;
- if (!force_printkthreads() &&
- printing_via_unlock &&
- !is_printk_deferred()) {
- if (console_trylock()) {
- do_trigger_flush = false;
- console_unlock();
- }
- }
- }
-
if (!WARN_ON_ONCE(*cpu_emergency_nesting == 0))
(*cpu_emergency_nesting)--;
preempt_enable();
-
- if (do_trigger_flush)
- printk_trigger_flush();
}
/**
- * nbcon_cpu_emergency_flush - Explicitly flush consoles while
- * within emergency context
+ * nbcon_alloc - Allocate and init the nbcon console specific data
+ * @con: Console to initialize
*
- * Both nbcon and legacy consoles are flushed.
+ * Return: True if the console was fully allocated and initialized.
+ * Otherwise @con must not be registered.
*
- * It should be used only when there are too many messages printed
- * in emergency context, for example, printing backtraces of all
- * CPUs or processes. It is typically needed when the watchdogs
- * need to be touched as well.
- */
-void nbcon_cpu_emergency_flush(void)
-{
- bool is_emergency;
-
- /*
- * If this context is not an emergency context, preemption might be
- * enabled. To be sure, disable preemption when checking if this is
- * an emergency context.
- */
- preempt_disable();
- is_emergency = (*nbcon_get_cpu_emergency_nesting() != 0);
- preempt_enable();
-
- /* The explicit flush is needed only in the emergency context. */
- if (!is_emergency)
- return;
-
- nbcon_atomic_flush_pending();
-
- if (!force_printkthreads() &&
- printing_via_unlock &&
- !is_printk_deferred()) {
- if (console_trylock())
- console_unlock();
- }
-}
-
-/*
- * nbcon_kthread_stop - Stop a printer thread
- * @con: Console to operate on
- */
-static void nbcon_kthread_stop(struct console *con)
-{
- lockdep_assert_console_list_lock_held();
-
- if (!con->kthread)
- return;
-
- kthread_stop(con->kthread);
- con->kthread = NULL;
-}
-
-/**
- * nbcon_kthread_create - Create a printer thread
- * @con: Console to operate on
- *
- * If it fails, let the console proceed. The atomic part might
- * be usable and useful.
- */
-void nbcon_kthread_create(struct console *con)
-{
- struct task_struct *kt;
-
- lockdep_assert_console_list_lock_held();
-
- if (!(con->flags & CON_NBCON) || !con->write_thread)
- return;
-
- if (!printk_threads_enabled || con->kthread)
- return;
-
- /*
- * Printer threads cannot be started as long as any boot console is
- * registered because there is no way to synchronize the hardware
- * registers between boot console code and regular console code.
- */
- if (have_boot_console)
- return;
-
- kt = kthread_run(nbcon_kthread_func, con, "pr/%s%d", con->name, con->index);
- if (IS_ERR(kt)) {
- con_printk(KERN_ERR, con, "failed to start printing thread\n");
- return;
- }
-
- con->kthread = kt;
-
- /*
- * It is important that console printing threads are scheduled
- * shortly after a printk call and with generous runtime budgets.
- */
- sched_set_normal(con->kthread, -20);
-}
-
-static int __init printk_setup_threads(void)
-{
- struct console *con;
-
- console_list_lock();
- printk_threads_enabled = true;
- for_each_console(con)
- nbcon_kthread_create(con);
- if (force_printkthreads() && printing_via_unlock)
- nbcon_legacy_kthread_create();
- console_list_unlock();
- return 0;
-}
-early_initcall(printk_setup_threads);
-
-/**
- * nbcon_alloc - Allocate buffers needed by the nbcon console
- * @con: Console to allocate buffers for
- *
- * Return: True on success. False otherwise and the console cannot
- * be used.
- *
- * This is not part of nbcon_init() because buffer allocation must
- * be performed earlier in the console registration process.
+ * When allocation and init was successful, the console must be properly
+ * freed using nbcon_free() once it is no longer needed.
*/
bool nbcon_alloc(struct console *con)
{
+ struct nbcon_state state = { };
+
+ /* The write_thread() callback is mandatory. */
+ if (WARN_ON(!con->write_thread))
+ return false;
+
+ rcuwait_init(&con->rcuwait);
+ init_irq_work(&con->irq_work, nbcon_irq_work);
+ atomic_long_set(&ACCESS_PRIVATE(con, nbcon_prev_seq), -1UL);
+ nbcon_state_set(con, &state);
+
+ /*
+ * Initialize @nbcon_seq to the highest possible sequence number so
+ * that practically speaking it will have nothing to print until a
+ * desired initial sequence number has been set via nbcon_seq_force().
+ */
+ atomic_long_set(&ACCESS_PRIVATE(con, nbcon_seq), ULSEQ_MAX(prb));
+
if (con->flags & CON_BOOT) {
/*
* Boot console printing is synchronized with legacy console
@@ -1704,34 +1692,18 @@ bool nbcon_alloc(struct console *con)
con_printk(KERN_ERR, con, "failed to allocate printing buffer\n");
return false;
}
+
+ if (printk_kthreads_running) {
+ if (!nbcon_kthread_create(con)) {
+ kfree(con->pbufs);
+ return false;
+ }
+ }
}
return true;
}
-/**
- * nbcon_init - Initialize the nbcon console specific data
- * @con: Console to initialize
- * @init_seq: Sequence number of the first record to be emitted
- *
- * nbcon_alloc() *must* be called and succeed before this function
- * is called.
- */
-void nbcon_init(struct console *con, u64 init_seq)
-{
- struct nbcon_state state = { };
-
- /* nbcon_alloc() must have been called and successful! */
- BUG_ON(!con->pbufs);
-
- rcuwait_init(&con->rcuwait);
- init_irq_work(&con->irq_work, nbcon_irq_work);
- nbcon_seq_force(con, init_seq);
- atomic_long_set(&ACCESS_PRIVATE(con, nbcon_prev_seq), -1UL);
- nbcon_state_set(con, &state);
- nbcon_kthread_create(con);
-}
-
/**
* nbcon_free - Free and cleanup the nbcon console specific data
* @con: Console to free/cleanup nbcon data
@@ -1740,7 +1712,9 @@ void nbcon_free(struct console *con)
{
struct nbcon_state state = { };
- nbcon_kthread_stop(con);
+ if (printk_kthreads_running)
+ nbcon_kthread_stop(con);
+
nbcon_state_set(con, &state);
/* Boot consoles share global printk buffers. */
@@ -1796,6 +1770,7 @@ EXPORT_SYMBOL_GPL(nbcon_device_try_acquire);
void nbcon_device_release(struct console *con)
{
struct nbcon_context *ctxt = &ACCESS_PRIVATE(con, nbcon_device_ctxt);
+ struct console_flush_type ft;
int cookie;
if (!nbcon_context_exit_unsafe(ctxt))
@@ -1805,45 +1780,28 @@ void nbcon_device_release(struct console *con)
/*
* This context must flush any new records added while the console
- * was locked. The console_srcu_read_lock must be taken to ensure
- * the console is usable throughout flushing.
+ * was locked if the printer thread is not available to do it. The
+ * console_srcu_read_lock must be taken to ensure the console is
+ * usable throughout flushing.
*/
cookie = console_srcu_read_lock();
+ printk_get_console_flush_type(&ft);
if (console_is_usable(con, console_srcu_read_flags(con), true) &&
- (!con->kthread || (system_state > SYSTEM_RUNNING)) &&
+ !ft.nbcon_offload &&
prb_read_valid(prb, nbcon_seq_read(con), NULL)) {
- __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false);
+ /*
+ * If nbcon_atomic flushing is not available, fallback to
+ * using the legacy loop.
+ */
+ if (ft.nbcon_atomic) {
+ __nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false);
+ } else if (ft.legacy_direct) {
+ if (console_trylock())
+ console_unlock();
+ } else if (ft.legacy_offload) {
+ printk_trigger_flush();
+ }
}
console_srcu_read_unlock(cookie);
}
EXPORT_SYMBOL_GPL(nbcon_device_release);
-
-/**
- * printk_kthread_shutdown - shutdown all threaded printers
- *
- * On system shutdown all threaded printers are stopped. This allows printk
- * to transition back to atomic printing, thus providing a robust mechanism
- * for the final shutdown/reboot messages to be output.
- */
-static void printk_kthread_shutdown(void)
-{
- struct console *con;
-
- console_list_lock();
- for_each_console(con) {
- if (con->flags & CON_NBCON)
- nbcon_kthread_stop(con);
- }
- console_list_unlock();
-}
-
-static struct syscore_ops printk_syscore_ops = {
- .shutdown = printk_kthread_shutdown,
-};
-
-static int __init printk_init_ops(void)
-{
- register_syscore_ops(&printk_syscore_ops);
- return 0;
-}
-device_initcall(printk_init_ops);
@@ -34,6 +34,7 @@
#include <linux/security.h>
#include <linux/memblock.h>
#include <linux/syscalls.h>
+#include <linux/syscore_ops.h>
#include <linux/vmcore_info.h>
#include <linux/ratelimit.h>
#include <linux/kmsg_dump.h>
@@ -195,17 +196,6 @@ static int __init control_devkmsg(char *str)
}
__setup("printk.devkmsg=", control_devkmsg);
-#if !defined(CONFIG_PREEMPT_RT)
-DEFINE_STATIC_KEY_FALSE(force_printkthreads_key);
-
-static int __init setup_forced_printkthreads(char *arg)
-{
- static_branch_enable(&force_printkthreads_key);
- return 0;
-}
-early_param("threadprintk", setup_forced_printkthreads);
-#endif
-
char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE] = "ratelimit";
#if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
int devkmsg_sysctl_set_loglvl(const struct ctl_table *table, int write,
@@ -486,7 +476,7 @@ bool have_legacy_console;
* synchronous printing of legacy consoles will not occur during panic until
* the backtrace has been stored to the ringbuffer.
*/
-static bool have_nbcon_console;
+bool have_nbcon_console;
/*
* Specifies if a boot console is registered. If boot consoles are present,
@@ -496,17 +486,21 @@ static bool have_nbcon_console;
*/
bool have_boot_console;
+/* See printk_legacy_allow_panic_sync() for details. */
+bool legacy_allow_panic_sync;
+
#ifdef CONFIG_PRINTK
DECLARE_WAIT_QUEUE_HEAD(log_wait);
-
static DECLARE_WAIT_QUEUE_HEAD(legacy_wait);
-
/* All 3 protected by @syslog_lock. */
/* the next printk record to read by syslog(READ) or /proc/kmsg */
static u64 syslog_seq;
static size_t syslog_partial;
static bool syslog_time;
+/* True when _all_ printer threads are available for printing. */
+bool printk_kthreads_running;
+
struct latched_seq {
seqcount_latch_t latch;
u64 val[2];
@@ -2338,8 +2332,6 @@ int vprintk_store(int facility, int level,
return ret;
}
-static bool legacy_allow_panic_sync;
-
/*
* This acts as a one-way switch to allow legacy consoles to print from
* the printk() caller context on a panic CPU. It also attempts to flush
@@ -2347,9 +2339,12 @@ static bool legacy_allow_panic_sync;
*/
void printk_legacy_allow_panic_sync(void)
{
+ struct console_flush_type ft;
+
legacy_allow_panic_sync = true;
- if (printing_via_unlock && !in_nmi()) {
+ printk_get_console_flush_type(&ft);
+ if (ft.legacy_direct) {
if (console_trylock())
console_unlock();
}
@@ -2359,8 +2354,7 @@ asmlinkage int vprintk_emit(int facility, int level,
const struct dev_printk_info *dev_info,
const char *fmt, va_list args)
{
- bool do_trylock_unlock = !force_printkthreads() &&
- printing_via_unlock;
+ struct console_flush_type ft;
int printed_len;
/* Suppress unimportant messages after panic happens */
@@ -2375,87 +2369,49 @@ asmlinkage int vprintk_emit(int facility, int level,
if (other_cpu_in_panic() && !panic_triggering_all_cpu_backtrace)
return 0;
+ printk_get_console_flush_type(&ft);
+
+ /* If called from the scheduler, we can not call up(). */
if (level == LOGLEVEL_SCHED) {
level = LOGLEVEL_DEFAULT;
- /* If called from the scheduler, we can not call up(). */
- do_trylock_unlock = false;
+ ft.legacy_offload |= ft.legacy_direct;
+ ft.legacy_direct = false;
}
printk_delay(level);
printed_len = vprintk_store(facility, level, dev_info, fmt, args);
- if (have_nbcon_console && !have_boot_console) {
- bool is_panic_context = this_cpu_in_panic();
+ if (ft.nbcon_atomic)
+ nbcon_atomic_flush_pending();
- /*
- * In panic, the legacy consoles are not allowed to print from
- * the printk calling context unless explicitly allowed. This
- * gives the safe nbcon consoles a chance to print out all the
- * panic messages first. This restriction only applies if
- * there are nbcon consoles registered.
- */
- if (is_panic_context)
- do_trylock_unlock &= legacy_allow_panic_sync;
+ if (ft.nbcon_offload)
+ nbcon_kthreads_wake();
- /*
- * There are situations where nbcon atomic printing should
- * happen in the printk() caller context:
- *
- * - When this CPU is in panic.
- *
- * - When booting, before the printing threads have been
- * started.
- *
- * - During shutdown, since the printing threads may not get
- * a chance to print the final messages.
- *
- * Note that if boot consoles are registered, the console
- * lock/unlock dance must be relied upon instead because nbcon
- * consoles cannot print simultaneously with boot consoles.
- */
- if (is_panic_context ||
- !printk_threads_enabled ||
- (system_state > SYSTEM_RUNNING)) {
- nbcon_atomic_flush_pending();
- }
- }
-
- nbcon_wake_threads();
-
- if (do_trylock_unlock) {
+ if (ft.legacy_direct) {
/*
* The caller may be holding system-critical or
* timing-sensitive locks. Disable preemption during
* printing of all remaining records to all consoles so that
* this context can return as soon as possible. Hopefully
* another printk() caller will take over the printing.
- *
- * Also, nbcon_get_default_prio() requires migration disabled.
*/
preempt_disable();
-
/*
* Try to acquire and then immediately release the console
* semaphore. The release will print out buffers. With the
* spinning variant, this context tries to take over the
* printing from another printing context.
- *
- * Skip it in EMERGENCY priority. The console will be
- * explicitly flushed when exiting the emergency section.
*/
- if (nbcon_get_default_prio() != NBCON_PRIO_EMERGENCY) {
- if (console_trylock_spinning())
- console_unlock();
- }
-
+ if (console_trylock_spinning())
+ console_unlock();
preempt_enable();
}
- if (do_trylock_unlock)
- wake_up_klogd();
- else
+ if (ft.legacy_offload)
defer_console_output();
+ else
+ wake_up_klogd();
return printed_len;
}
@@ -2483,14 +2439,6 @@ EXPORT_SYMBOL(_printk);
static bool pr_flush(int timeout_ms, bool reset_on_progress);
static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress);
-static struct task_struct *nbcon_legacy_kthread;
-
-static inline void wake_up_legacy_kthread(void)
-{
- if (nbcon_legacy_kthread)
- wake_up_interruptible(&legacy_wait);
-}
-
#else /* CONFIG_PRINTK */
#define printk_time false
@@ -2503,9 +2451,8 @@ static u64 syslog_seq;
static bool pr_flush(int timeout_ms, bool reset_on_progress) { return true; }
static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) { return true; }
+static inline void legacy_kthread_wake(void) { }
-static inline void nbcon_legacy_kthread_create(void) { }
-static inline void wake_up_legacy_kthread(void) { }
#endif /* CONFIG_PRINTK */
#ifdef CONFIG_EARLY_PRINTK
@@ -2790,9 +2737,8 @@ void suspend_console(void)
void resume_console(void)
{
+ struct console_flush_type ft;
struct console *con;
- short flags;
- int cookie;
if (!console_suspend_enabled)
return;
@@ -2809,19 +2755,11 @@ void resume_console(void)
*/
synchronize_srcu(&console_srcu);
- /*
- * Since this runs in task context, wake the threaded printers
- * directly rather than scheduling irq_work to do it.
- */
- cookie = console_srcu_read_lock();
- for_each_console_srcu(con) {
- flags = console_srcu_read_flags(con);
- if (flags & CON_NBCON)
- nbcon_kthread_wake(con);
- }
- console_srcu_read_unlock(cookie);
-
- wake_up_legacy_kthread();
+ printk_get_console_flush_type(&ft);
+ if (ft.nbcon_offload)
+ nbcon_kthreads_wake();
+ if (ft.legacy_offload)
+ defer_console_output();
pr_flush(1000, true);
}
@@ -2837,12 +2775,16 @@ void resume_console(void)
*/
static int console_cpu_notify(unsigned int cpu)
{
- if (!force_printkthreads() &&
- !cpuhp_tasks_frozen &&
- printing_via_unlock) {
- /* If trylock fails, someone else is doing the printing */
- if (console_trylock())
- console_unlock();
+ struct console_flush_type ft;
+
+ if (!cpuhp_tasks_frozen) {
+ printk_get_console_flush_type(&ft);
+ if (ft.nbcon_atomic)
+ nbcon_atomic_flush_pending();
+ if (ft.legacy_direct) {
+ if (console_trylock())
+ console_unlock();
+ }
}
return 0;
}
@@ -2905,25 +2847,31 @@ static void __console_unlock(void)
#ifdef CONFIG_PRINTK
/*
- * Prepend the message in @pmsg->pbufs->outbuf with the message in
- * @pmsg->pbufs->scratchbuf. This is achieved by shifting the existing message
- * over and inserting the scratchbuf message.
+ * Prepend the message in @pmsg->pbufs->outbuf. This is achieved by shifting
+ * the existing message over and inserting the scratchbuf message.
*
- * @pmsg is the printk message to prepend.
+ * @pmsg is the original printk message.
+ * @fmt is the printf format of the message which will prepend the existing one.
*
- * @len is the length of the message in @pmsg->pbufs->scratchbuf.
- *
- * If the message text in @pmsg->pbufs->outbuf does not have enough space for
- * the scratchbuf message, the message text will be sufficiently truncated.
+ * If there is not enough space in @pmsg->pbufs->outbuf, the existing
+ * message text will be sufficiently truncated.
*
* If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
*/
-static void __console_prepend_scratch(struct printk_message *pmsg, size_t len)
+__printf(2, 3)
+static void console_prepend_message(struct printk_message *pmsg, const char *fmt, ...)
{
struct printk_buffers *pbufs = pmsg->pbufs;
+ const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
const size_t outbuf_sz = sizeof(pbufs->outbuf);
char *scratchbuf = &pbufs->scratchbuf[0];
char *outbuf = &pbufs->outbuf[0];
+ va_list args;
+ size_t len;
+
+ va_start(args, fmt);
+ len = vscnprintf(scratchbuf, scratchbuf_sz, fmt, args);
+ va_end(args);
/*
* Make sure outbuf is sufficiently large before prepending.
@@ -2955,15 +2903,7 @@ static void __console_prepend_scratch(struct printk_message *pmsg, size_t len)
*/
void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
{
- struct printk_buffers *pbufs = pmsg->pbufs;
- const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
- char *scratchbuf = &pbufs->scratchbuf[0];
- size_t len;
-
- len = scnprintf(scratchbuf, scratchbuf_sz,
- "** %lu printk messages dropped **\n", dropped);
-
- __console_prepend_scratch(pmsg, len);
+ console_prepend_message(pmsg, "** %lu printk messages dropped **\n", dropped);
}
/*
@@ -2974,15 +2914,7 @@ void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
*/
void console_prepend_replay(struct printk_message *pmsg)
{
- struct printk_buffers *pbufs = pmsg->pbufs;
- const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
- char *scratchbuf = &pbufs->scratchbuf[0];
- size_t len;
-
- len = scnprintf(scratchbuf, scratchbuf_sz,
- "** replaying previous printk message **\n");
-
- __console_prepend_scratch(pmsg, len);
+ console_prepend_message(pmsg, "** replaying previous printk message **\n");
}
/*
@@ -3056,22 +2988,23 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
* false positive. For PREEMPT_RT the false positive condition does not
* occur.
*
- * This map is used to establish LD_WAIT_SLEEP context for the console write
- * callbacks when legacy printing to avoid false positive lockdep complaints,
- * thus allowing lockdep to continue to function for real issues.
+ * This map is used to temporarily establish LD_WAIT_SLEEP context for the
+ * console write() callback when legacy printing to avoid false positive
+ * lockdep complaints, thus allowing lockdep to continue to function for
+ * real issues.
*/
#ifdef CONFIG_PREEMPT_RT
-static inline void printk_legacy_lock_map_acquire_try(void) { }
-static inline void printk_legacy_lock_map_release(void) { }
+static inline void printk_legacy_allow_spinlock_enter(void) { }
+static inline void printk_legacy_allow_spinlock_exit(void) { }
#else
static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_SLEEP);
-static inline void printk_legacy_lock_map_acquire_try(void)
+static inline void printk_legacy_allow_spinlock_enter(void)
{
lock_map_acquire_try(&printk_legacy_map);
}
-static inline void printk_legacy_lock_map_release(void)
+static inline void printk_legacy_allow_spinlock_exit(void)
{
lock_map_release(&printk_legacy_map);
}
@@ -3128,11 +3061,12 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co
/* Write everything out to the hardware. */
- if (force_printkthreads()) {
+ if (force_legacy_kthread() && !panic_in_progress()) {
/*
- * With forced threading this function is either in a thread
- * or panic context. So there is no need for concern about
- * printk reentrance, handovers, or lockdep complaints.
+ * With forced threading this function is in a task context
+ * (either legacy kthread or get_init_console_seq()). There
+ * is no need for concern about printk reentrance, handovers,
+ * or lockdep complaints.
*/
con->write(con, outbuf, pmsg.outbuf_len);
@@ -3154,9 +3088,9 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co
/* Do not trace print latency. */
stop_critical_timings();
- printk_legacy_lock_map_acquire_try();
+ printk_legacy_allow_spinlock_enter();
con->write(con, outbuf, pmsg.outbuf_len);
- printk_legacy_lock_map_release();
+ printk_legacy_allow_spinlock_exit();
start_critical_timings();
@@ -3177,6 +3111,8 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co
return false;
}
+static inline void printk_kthreads_check_locked(void) { }
+
#endif /* CONFIG_PRINTK */
/*
@@ -3204,6 +3140,7 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co
*/
static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
{
+ struct console_flush_type ft;
bool any_usable = false;
struct console *con;
bool any_progress;
@@ -3215,6 +3152,8 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
do {
any_progress = false;
+ printk_get_console_flush_type(&ft);
+
cookie = console_srcu_read_lock();
for_each_console_srcu(con) {
short flags = console_srcu_read_flags(con);
@@ -3222,10 +3161,10 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
bool progress;
/*
- * console_flush_all() is only for legacy consoles,
- * unless the nbcon console has no kthread printer.
+ * console_flush_all() is only for legacy consoles when
+ * the nbcon consoles have their printer threads.
*/
- if ((flags & CON_NBCON) && con->kthread)
+ if ((flags & CON_NBCON) && ft.nbcon_offload)
continue;
if (!console_is_usable(con, flags, !do_cond_resched))
@@ -3273,7 +3212,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
return false;
}
-static void console_flush_and_unlock(void)
+static void __console_flush_and_unlock(void)
{
bool do_cond_resched;
bool handover;
@@ -3319,29 +3258,26 @@ static void console_flush_and_unlock(void)
}
/**
- * console_unlock - unblock the console subsystem from printing
+ * console_unlock - unblock the legacy console subsystem from printing
*
* Releases the console_lock which the caller holds to block printing of
- * the console subsystem.
+ * the legacy console subsystem.
*
* While the console_lock was held, console output may have been buffered
- * by printk(). If this is the case, console_unlock(); emits
- * the output prior to releasing the lock.
+ * by printk(). If this is the case, console_unlock() emits the output on
+ * legacy consoles prior to releasing the lock.
*
* console_unlock(); may be called from any context.
*/
void console_unlock(void)
{
- /*
- * Forced threading relies on kthread and atomic consoles for
- * printing. It never attempts to print from console_unlock().
- */
- if (force_printkthreads()) {
- __console_unlock();
- return;
- }
+ struct console_flush_type ft;
- console_flush_and_unlock();
+ printk_get_console_flush_type(&ft);
+ if (ft.legacy_direct)
+ __console_flush_and_unlock();
+ else
+ __console_unlock();
}
EXPORT_SYMBOL(console_unlock);
@@ -3465,6 +3401,7 @@ static void __console_rewind_all(void)
*/
void console_flush_on_panic(enum con_flush_mode mode)
{
+ struct console_flush_type ft;
bool handover;
u64 next_seq;
@@ -3488,9 +3425,12 @@ void console_flush_on_panic(enum con_flush_mode mode)
if (mode == CONSOLE_REPLAY_ALL)
__console_rewind_all();
- nbcon_atomic_flush_pending();
+ printk_get_console_flush_type(&ft);
+ if (ft.nbcon_atomic)
+ nbcon_atomic_flush_pending();
- if (printing_via_unlock)
+ /* Flush legacy consoles once allowed, even when dangerous. */
+ if (legacy_allow_panic_sync)
console_flush_all(false, &next_seq, &handover);
}
@@ -3548,11 +3488,12 @@ EXPORT_SYMBOL(console_stop);
void console_start(struct console *console)
{
- short flags;
- int cookie;
+ struct console_flush_type ft;
+ bool is_nbcon;
console_list_lock();
console_srcu_write_flags(console, console->flags | CON_ENABLED);
+ is_nbcon = console->flags & CON_NBCON;
console_list_unlock();
/*
@@ -3562,38 +3503,46 @@ void console_start(struct console *console)
*/
synchronize_srcu(&console_srcu);
- cookie = console_srcu_read_lock();
- flags = console_srcu_read_flags(console);
- if (flags & CON_NBCON)
+ printk_get_console_flush_type(&ft);
+ if (is_nbcon && ft.nbcon_offload)
nbcon_kthread_wake(console);
- else
- wake_up_legacy_kthread();
- console_srcu_read_unlock(cookie);
+ else if (!is_nbcon && ft.legacy_offload)
+ defer_console_output();
__pr_flush(console, 1000, true);
}
EXPORT_SYMBOL(console_start);
#ifdef CONFIG_PRINTK
-static bool printer_should_wake(void)
+static int unregister_console_locked(struct console *console);
+
+/* True when system boot is far enough to create printer threads. */
+static bool printk_kthreads_ready __ro_after_init;
+
+static struct task_struct *printk_legacy_kthread;
+
+static bool legacy_kthread_should_wakeup(void)
{
- bool available = false;
+ struct console_flush_type ft;
struct console *con;
+ bool ret = false;
int cookie;
if (kthread_should_stop())
return true;
+ printk_get_console_flush_type(&ft);
+
cookie = console_srcu_read_lock();
for_each_console_srcu(con) {
short flags = console_srcu_read_flags(con);
u64 printk_seq;
/*
- * The legacy printer thread is only for legacy consoles,
- * unless the nbcon console has no kthread printer.
+ * The legacy printer thread is only for legacy consoles when
+ * the nbcon consoles have their printer threads.
*/
- if ((flags & CON_NBCON) && con->kthread)
+ if ((flags & CON_NBCON) && ft.nbcon_offload)
continue;
if (!console_is_usable(con, flags, false))
@@ -3610,61 +3559,162 @@ static bool printer_should_wake(void)
}
if (prb_read_valid(prb, printk_seq, NULL)) {
- available = true;
+ ret = true;
break;
}
}
console_srcu_read_unlock(cookie);
- return available;
+ return ret;
}
-static int nbcon_legacy_kthread_func(void *unused)
+static int legacy_kthread_func(void *unused)
{
- int error;
-
for (;;) {
- error = wait_event_interruptible(legacy_wait, printer_should_wake());
+ wait_event_interruptible(legacy_wait, legacy_kthread_should_wakeup());
if (kthread_should_stop())
break;
- if (error)
- continue;
-
console_lock();
- console_flush_and_unlock();
+ __console_flush_and_unlock();
}
return 0;
}
-void nbcon_legacy_kthread_create(void)
+static bool legacy_kthread_create(void)
{
struct task_struct *kt;
- lockdep_assert_held(&console_mutex);
+ lockdep_assert_console_list_lock_held();
- if (!force_printkthreads())
- return;
-
- if (!printk_threads_enabled || nbcon_legacy_kthread)
- return;
-
- kt = kthread_run(nbcon_legacy_kthread_func, NULL, "pr/legacy");
- if (IS_ERR(kt)) {
- pr_err("unable to start legacy printing thread\n");
- return;
+ kt = kthread_run(legacy_kthread_func, NULL, "pr/legacy");
+ if (WARN_ON(IS_ERR(kt))) {
+ pr_err("failed to start legacy printing thread\n");
+ return false;
}
- nbcon_legacy_kthread = kt;
+ printk_legacy_kthread = kt;
/*
* It is important that console printing threads are scheduled
* shortly after a printk call and with generous runtime budgets.
*/
- sched_set_normal(nbcon_legacy_kthread, -20);
+ sched_set_normal(printk_legacy_kthread, -20);
+
+ return true;
}
+
+/**
+ * printk_kthreads_shutdown - shutdown all threaded printers
+ *
+ * On system shutdown all threaded printers are stopped. This allows printk
+ * to transition back to atomic printing, thus providing a robust mechanism
+ * for the final shutdown/reboot messages to be output.
+ */
+static void printk_kthreads_shutdown(void)
+{
+ struct console *con;
+
+ console_list_lock();
+ if (printk_kthreads_running) {
+ printk_kthreads_running = false;
+
+ for_each_console(con) {
+ if (con->flags & CON_NBCON)
+ nbcon_kthread_stop(con);
+ }
+
+ /*
+ * The threads may have been stopped while printing a
+ * backlog. Flush any records left over.
+ */
+ nbcon_atomic_flush_pending();
+ }
+ console_list_unlock();
+}
+
+static struct syscore_ops printk_syscore_ops = {
+ .shutdown = printk_kthreads_shutdown,
+};
+
+/*
+ * If appropriate, start nbcon kthreads and set @printk_kthreads_running.
+ * If any kthreads fail to start, those consoles are unregistered.
+ *
+ * Must be called under console_list_lock().
+ */
+static void printk_kthreads_check_locked(void)
+{
+ struct hlist_node *tmp;
+ struct console *con;
+
+ lockdep_assert_console_list_lock_held();
+
+ if (!printk_kthreads_ready)
+ return;
+
+ if (have_legacy_console || have_boot_console) {
+ if (!printk_legacy_kthread &&
+ force_legacy_kthread() &&
+ !legacy_kthread_create()) {
+ /*
+ * All legacy consoles must be unregistered. If there
+ * are any nbcon consoles, they will set up their own
+ * kthread.
+ */
+ hlist_for_each_entry_safe(con, tmp, &console_list, node) {
+ if (con->flags & CON_NBCON)
+ continue;
+
+ unregister_console_locked(con);
+ }
+ }
+ } else if (printk_legacy_kthread) {
+ kthread_stop(printk_legacy_kthread);
+ printk_legacy_kthread = NULL;
+ }
+
+ /*
+ * Printer threads cannot be started as long as any boot console is
+ * registered because there is no way to synchronize the hardware
+ * registers between boot console code and regular console code.
+ * It can only be known that there will be no new boot consoles when
+ * an nbcon console is registered.
+ */
+ if (have_boot_console || !have_nbcon_console) {
+ /* Clear flag in case all nbcon consoles unregistered. */
+ printk_kthreads_running = false;
+ return;
+ }
+
+ if (printk_kthreads_running)
+ return;
+
+ hlist_for_each_entry_safe(con, tmp, &console_list, node) {
+ if (!(con->flags & CON_NBCON))
+ continue;
+
+ if (!nbcon_kthread_create(con))
+ unregister_console_locked(con);
+ }
+
+ printk_kthreads_running = true;
+}
+
+static int __init printk_set_kthreads_ready(void)
+{
+ register_syscore_ops(&printk_syscore_ops);
+
+ console_list_lock();
+ printk_kthreads_ready = true;
+ printk_kthreads_check_locked();
+ console_list_unlock();
+
+ return 0;
+}
+early_initcall(printk_set_kthreads_ready);
#endif /* CONFIG_PRINTK */
static int __read_mostly keep_bootcon;
@@ -3955,11 +4005,10 @@ void register_console(struct console *newcon)
if (newcon->flags & CON_NBCON) {
have_nbcon_console = true;
- nbcon_init(newcon, init_seq);
+ nbcon_seq_force(newcon, init_seq);
} else {
have_legacy_console = true;
newcon->seq = init_seq;
- nbcon_legacy_kthread_create();
}
if (newcon->flags & CON_BOOT)
@@ -4026,6 +4075,9 @@ void register_console(struct console *newcon)
unregister_console_locked(con);
}
}
+
+ /* Changed console list, may require printer threads to start/stop. */
+ printk_kthreads_check_locked();
unlock:
console_list_unlock();
}
@@ -4035,7 +4087,6 @@ EXPORT_SYMBOL(register_console);
static int unregister_console_locked(struct console *console)
{
bool use_device_lock = (console->flags & CON_NBCON) && console->write_atomic;
- bool is_boot_con = (console->flags & CON_BOOT);
bool found_legacy_con = false;
bool found_nbcon_con = false;
bool found_boot_con = false;
@@ -4053,11 +4104,16 @@ static int unregister_console_locked(struct console *console)
if (res > 0)
return 0;
+ if (!console_is_registered_locked(console))
+ res = -ENODEV;
+ else if (console_is_usable(console, console->flags, true))
+ __pr_flush(console, 1000, true);
+
/* Disable it unconditionally */
console_srcu_write_flags(console, console->flags & ~CON_ENABLED);
- if (!console_is_registered_locked(console))
- return -ENODEV;
+ if (res < 0)
+ return res;
/*
* Use the driver synchronization to ensure that the hardware is not
@@ -4118,21 +4174,8 @@ static int unregister_console_locked(struct console *console)
if (!found_nbcon_con)
have_nbcon_console = found_nbcon_con;
- /*
- * When the last boot console unregisters, start up the
- * printing threads.
- */
- if (is_boot_con && !have_boot_console) {
- for_each_console(c)
- nbcon_kthread_create(c);
- }
-
-#ifdef CONFIG_PRINTK
- if (!printing_via_unlock && nbcon_legacy_kthread) {
- kthread_stop(nbcon_legacy_kthread);
- nbcon_legacy_kthread = NULL;
- }
-#endif
+ /* Changed console list, may require printer threads to start/stop. */
+ printk_kthreads_check_locked();
return res;
}
@@ -4280,6 +4323,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
{
unsigned long timeout_jiffies = msecs_to_jiffies(timeout_ms);
unsigned long remaining_jiffies = timeout_jiffies;
+ struct console_flush_type ft;
struct console *c;
u64 last_diff = 0;
u64 printk_seq;
@@ -4288,16 +4332,17 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
u64 diff;
u64 seq;
+ /* Sorry, pr_flush() will not work this early. */
+ if (system_state < SYSTEM_SCHEDULING)
+ return false;
+
might_sleep();
seq = prb_next_reserve_seq(prb);
- /*
- * Flush the consoles so that records up to @seq are printed.
- * Otherwise this function will just wait for the threaded printers
- * to print up to @seq.
- */
- if (printing_via_unlock) {
+ /* Flush the consoles so that records up to @seq are printed. */
+ printk_get_console_flush_type(&ft);
+ if (ft.legacy_direct) {
console_lock();
console_unlock();
}
@@ -4305,26 +4350,22 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
for (;;) {
unsigned long begin_jiffies;
unsigned long slept_jiffies;
- bool use_console_lock = printing_via_unlock;
-
- /*
- * Ensure the compiler does not optimize @use_console_lock to
- * be @printing_via_unlock since the latter can change at any
- * time.
- */
- barrier();
diff = 0;
- if (use_console_lock) {
- /*
- * Hold the console_lock to guarantee safe access to
- * console->seq. Releasing console_lock flushes more
- * records in case @seq is still not printed on all
- * usable consoles.
- */
- console_lock();
- }
+ /*
+ * Hold the console_lock to guarantee safe access to
+ * console->seq. Releasing console_lock flushes more
+ * records in case @seq is still not printed on all
+ * usable consoles.
+ *
+ * Holding the console_lock is not necessary if there
+ * are no legacy or boot consoles. However, such a
+ * console could register at any time. Always hold the
+ * console_lock as a precaution rather than
+ * synchronizing against register_console().
+ */
+ console_lock();
cookie = console_srcu_read_lock();
for_each_console_srcu(c) {
@@ -4346,7 +4387,6 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
if (flags & CON_NBCON) {
printk_seq = nbcon_seq_read(c);
} else {
- WARN_ON_ONCE(!use_console_lock);
printk_seq = c->seq;
}
@@ -4358,8 +4398,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
if (diff != last_diff && reset_on_progress)
remaining_jiffies = timeout_jiffies;
- if (use_console_lock)
- console_unlock();
+ console_unlock();
/* Note: @diff is 0 if there are no usable consoles. */
if (diff == 0 || remaining_jiffies == 0)
@@ -4406,18 +4445,20 @@ static bool pr_flush(int timeout_ms, bool reset_on_progress)
static DEFINE_PER_CPU(int, printk_pending);
+static void legacy_kthread_wake(void)
+{
+ if (printk_legacy_kthread)
+ wake_up_interruptible(&legacy_wait);
+}
+
static void wake_up_klogd_work_func(struct irq_work *irq_work)
{
int pending = this_cpu_xchg(printk_pending, 0);
if (pending & PRINTK_PENDING_OUTPUT) {
- if (force_printkthreads()) {
- wake_up_legacy_kthread();
+ if (force_legacy_kthread()) {
+ legacy_kthread_wake();
} else {
- /*
- * If trylock fails, some other context
- * will do the printing.
- */
if (console_trylock())
console_unlock();
}
@@ -4436,7 +4477,6 @@ static void __wake_up_klogd(int val)
return;
preempt_disable();
-
/*
* Guarantee any new records can be seen by tasks preparing to wait
* before this context checks if the wait queue is empty.
@@ -4448,22 +4488,11 @@ static void __wake_up_klogd(int val)
*
* This pairs with devkmsg_read:A and syslog_print:A.
*/
- if (!wq_has_sleeper(&log_wait)) /* LMM(__wake_up_klogd:A) */
- val &= ~PRINTK_PENDING_WAKEUP;
-
- /*
- * Simple read is safe. register_console() would flush a newly
- * registered legacy console when writing the message about it
- * being enabled.
- */
- if (!printing_via_unlock)
- val &= ~PRINTK_PENDING_OUTPUT;
-
- if (val) {
+ if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
+ (val & PRINTK_PENDING_OUTPUT)) {
this_cpu_or(printk_pending, val);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
}
-
preempt_enable();
}
@@ -4505,7 +4534,6 @@ void defer_console_output(void)
void printk_trigger_flush(void)
{
- nbcon_wake_threads();
defer_console_output();
}
@@ -4839,9 +4867,15 @@ EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
*/
void console_try_replay_all(void)
{
+ struct console_flush_type ft;
+
+ printk_get_console_flush_type(&ft);
if (console_trylock()) {
__console_rewind_all();
- nbcon_wake_threads();
+ if (ft.nbcon_offload)
+ nbcon_kthreads_wake();
+ if (ft.legacy_offload)
+ defer_console_output();
/* Consoles are flushed as part of console_unlock(). */
console_unlock();
}
@@ -403,10 +403,12 @@ u64 prb_next_reserve_seq(struct printk_ringbuffer *rb);
#define __u64seq_to_ulseq(u64seq) (u64seq)
#define __ulseq_to_u64seq(rb, ulseq) (ulseq)
+#define ULSEQ_MAX(rb) (-1)
#else /* CONFIG_64BIT */
#define __u64seq_to_ulseq(u64seq) ((u32)u64seq)
+#define ULSEQ_MAX(rb) __u64seq_to_ulseq(prb_first_seq(rb) + 0x80000000UL)
static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq)
{
@@ -38,13 +38,15 @@ void __printk_deferred_exit(void)
__printk_safe_exit();
}
-bool is_printk_deferred(void)
+bool is_printk_legacy_deferred(void)
{
/*
* The per-CPU variable @printk_context can be read safely in any
- * context. The CPU migration always disabled when set.
+ * context. CPU migration is always disabled when set.
*/
- return (this_cpu_read(printk_context) || in_nmi());
+ return (force_legacy_kthread() ||
+ this_cpu_read(printk_context) ||
+ in_nmi());
}
asmlinkage int vprintk(const char *fmt, va_list args)
@@ -59,7 +61,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
* Use the main logbuf even in NMI. But avoid calling console
* drivers that might have their own locks.
*/
- if (is_printk_deferred())
+ if (is_printk_legacy_deferred())
return vprintk_deferred(fmt, args);
/* No obstacles. */
@@ -643,7 +643,6 @@ static void synchronize_rcu_expedited_wait(void)
preempt_disable(); // For smp_processor_id() in dump_cpu_task().
dump_cpu_task(cpu);
preempt_enable();
- nbcon_cpu_emergency_flush();
}
rcu_exp_print_detail_task_stall_rnp(rnp);
}
@@ -819,7 +818,6 @@ static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp)
*/
touch_nmi_watchdog();
sched_show_task(t);
- nbcon_cpu_emergency_flush();
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
@@ -261,7 +261,6 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
*/
touch_nmi_watchdog();
sched_show_task(t);
- nbcon_cpu_emergency_flush();
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
@@ -525,7 +524,6 @@ static void print_cpu_stall_info(int cpu)
falsepositive ? " (false positive?)" : "");
print_cpu_stat_info(cpu);
- nbcon_cpu_emergency_flush();
}
/* Complain about starvation of grace-period kthread. */
@@ -1 +1 @@
--rt4
+-rt5
@@ -8,7 +8,7 @@
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
-#include <linux/seqlock.h>
+#include <linux/u64_stats_sync.h>
#include <linux/netlink.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nf_tables.h>
@@ -17,6 +17,11 @@
#include <net/netfilter/nf_tables_offload.h>
struct nft_counter {
+ u64_stats_t bytes;
+ u64_stats_t packets;
+};
+
+struct nft_counter_tot {
s64 bytes;
s64 packets;
};
@@ -25,25 +30,24 @@ struct nft_counter_percpu_priv {
struct nft_counter __percpu *counter;
};
-static DEFINE_PER_CPU(seqcount_t, nft_counter_seq);
+static DEFINE_PER_CPU(struct u64_stats_sync, nft_counter_sync);
static inline void nft_counter_do_eval(struct nft_counter_percpu_priv *priv,
struct nft_regs *regs,
const struct nft_pktinfo *pkt)
{
+ struct u64_stats_sync *nft_sync;
struct nft_counter *this_cpu;
- seqcount_t *myseq;
local_bh_disable();
this_cpu = this_cpu_ptr(priv->counter);
- myseq = this_cpu_ptr(&nft_counter_seq);
+ nft_sync = this_cpu_ptr(&nft_counter_sync);
- write_seqcount_begin(myseq);
+ u64_stats_update_begin(nft_sync);
+ u64_stats_add(&this_cpu->bytes, pkt->skb->len);
+ u64_stats_inc(&this_cpu->packets);
+ u64_stats_update_end(nft_sync);
- this_cpu->bytes += pkt->skb->len;
- this_cpu->packets++;
-
- write_seqcount_end(myseq);
local_bh_enable();
}
@@ -66,17 +70,16 @@ static int nft_counter_do_init(const struct nlattr * const tb[],
if (cpu_stats == NULL)
return -ENOMEM;
- preempt_disable();
- this_cpu = this_cpu_ptr(cpu_stats);
+ this_cpu = raw_cpu_ptr(cpu_stats);
if (tb[NFTA_COUNTER_PACKETS]) {
- this_cpu->packets =
- be64_to_cpu(nla_get_be64(tb[NFTA_COUNTER_PACKETS]));
+ u64_stats_set(&this_cpu->packets,
+ be64_to_cpu(nla_get_be64(tb[NFTA_COUNTER_PACKETS])));
}
if (tb[NFTA_COUNTER_BYTES]) {
- this_cpu->bytes =
- be64_to_cpu(nla_get_be64(tb[NFTA_COUNTER_BYTES]));
+ u64_stats_set(&this_cpu->bytes,
+ be64_to_cpu(nla_get_be64(tb[NFTA_COUNTER_BYTES])));
}
- preempt_enable();
+
priv->counter = cpu_stats;
return 0;
}
@@ -104,40 +107,41 @@ static void nft_counter_obj_destroy(const struct nft_ctx *ctx,
}
static void nft_counter_reset(struct nft_counter_percpu_priv *priv,
- struct nft_counter *total)
+ struct nft_counter_tot *total)
{
+ struct u64_stats_sync *nft_sync;
struct nft_counter *this_cpu;
- seqcount_t *myseq;
local_bh_disable();
this_cpu = this_cpu_ptr(priv->counter);
- myseq = this_cpu_ptr(&nft_counter_seq);
+ nft_sync = this_cpu_ptr(&nft_counter_sync);
+
+ u64_stats_update_begin(nft_sync);
+ u64_stats_add(&this_cpu->packets, -total->packets);
+ u64_stats_add(&this_cpu->bytes, -total->bytes);
+ u64_stats_update_end(nft_sync);
- write_seqcount_begin(myseq);
- this_cpu->packets -= total->packets;
- this_cpu->bytes -= total->bytes;
- write_seqcount_end(myseq);
local_bh_enable();
}
static void nft_counter_fetch(struct nft_counter_percpu_priv *priv,
- struct nft_counter *total)
+ struct nft_counter_tot *total)
{
struct nft_counter *this_cpu;
- const seqcount_t *myseq;
u64 bytes, packets;
unsigned int seq;
int cpu;
memset(total, 0, sizeof(*total));
for_each_possible_cpu(cpu) {
- myseq = per_cpu_ptr(&nft_counter_seq, cpu);
+ struct u64_stats_sync *nft_sync = per_cpu_ptr(&nft_counter_sync, cpu);
+
this_cpu = per_cpu_ptr(priv->counter, cpu);
do {
- seq = read_seqcount_begin(myseq);
- bytes = this_cpu->bytes;
- packets = this_cpu->packets;
- } while (read_seqcount_retry(myseq, seq));
+ seq = u64_stats_fetch_begin(nft_sync);
+ bytes = u64_stats_read(&this_cpu->bytes);
+ packets = u64_stats_read(&this_cpu->packets);
+ } while (u64_stats_fetch_retry(nft_sync, seq));
total->bytes += bytes;
total->packets += packets;
@@ -148,7 +152,7 @@ static int nft_counter_do_dump(struct sk_buff *skb,
struct nft_counter_percpu_priv *priv,
bool reset)
{
- struct nft_counter total;
+ struct nft_counter_tot total;
nft_counter_fetch(priv, &total);
@@ -237,7 +241,7 @@ static int nft_counter_clone(struct nft_expr *dst, const struct nft_expr *src, g
struct nft_counter_percpu_priv *priv_clone = nft_expr_priv(dst);
struct nft_counter __percpu *cpu_stats;
struct nft_counter *this_cpu;
- struct nft_counter total;
+ struct nft_counter_tot total;
nft_counter_fetch(priv, &total);
@@ -245,11 +249,9 @@ static int nft_counter_clone(struct nft_expr *dst, const struct nft_expr *src, g
if (cpu_stats == NULL)
return -ENOMEM;
- preempt_disable();
- this_cpu = this_cpu_ptr(cpu_stats);
- this_cpu->packets = total.packets;
- this_cpu->bytes = total.bytes;
- preempt_enable();
+ this_cpu = raw_cpu_ptr(cpu_stats);
+ u64_stats_set(&this_cpu->packets, total.packets);
+ u64_stats_set(&this_cpu->bytes, total.bytes);
priv_clone->counter = cpu_stats;
return 0;
@@ -267,17 +269,17 @@ static void nft_counter_offload_stats(struct nft_expr *expr,
const struct flow_stats *stats)
{
struct nft_counter_percpu_priv *priv = nft_expr_priv(expr);
+ struct u64_stats_sync *nft_sync;
struct nft_counter *this_cpu;
- seqcount_t *myseq;
local_bh_disable();
this_cpu = this_cpu_ptr(priv->counter);
- myseq = this_cpu_ptr(&nft_counter_seq);
+ nft_sync = this_cpu_ptr(&nft_counter_sync);
- write_seqcount_begin(myseq);
- this_cpu->packets += stats->pkts;
- this_cpu->bytes += stats->bytes;
- write_seqcount_end(myseq);
+ u64_stats_update_begin(nft_sync);
+ u64_stats_add(&this_cpu->packets, stats->pkts);
+ u64_stats_add(&this_cpu->bytes, stats->bytes);
+ u64_stats_update_end(nft_sync);
local_bh_enable();
}
@@ -286,7 +288,7 @@ void nft_counter_init_seqcount(void)
int cpu;
for_each_possible_cpu(cpu)
- seqcount_init(per_cpu_ptr(&nft_counter_seq, cpu));
+ u64_stats_init(per_cpu_ptr(&nft_counter_sync, cpu));
}
struct nft_expr_type nft_counter_type;
Dear RT folks! I'm pleased to announce the v6.11-rc5-rt5 patch set. Changes since v6.11-rc5-rt4: - Update John's printk series: - Removed "threadprintk" boot argument to force threaded printing of legacy console drivers on !CONFIG_PREEMPT_RT. - Reverted delayed flushing in emergency mode. For non-panic emergencies (WARN, RCU stall, lockdep splat) the emergency message lines are now printed synchronously, rather than buffering the full emergency message block and then flushing synchronously. - Switched to the lockless RCU API when detecting if printk threads are waiting. - Re-implemented logic for determining the flush type into a common helper function to provide consistent flushing behavior. - Re-implemented kthread starting/stopping for clean and reliable transitions between atomic and threaded printing. - Use lockless stats for nft_counter (netfilter). Known issues None. The delta patch against v6.11-rc5-rt4 is appended below and can be found here: https://cdn.kernel.org/pub/linux/kernel/projects/rt/6.11/incr/patch-6.11-rc5-rt4-rt5.patch.xz You can get this release via the git tree at: https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git v6.11-rc5-rt5 The RT patch against v6.11-rc5 can be found here: https://cdn.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patch-6.11-rc5-rt5.patch.xz The split quilt queue is available at: https://cdn.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patches-6.11-rc5-rt5.tar.xz Sebastian