| Message ID | 20190821092409.13225-3-julien.grall@arm.com |
|---|---|
| State | New |
| Headers | show |
| Series | hrtimer: RT fixes for hrtimer_grab_expiry_lock() | expand |
On 2019-08-21 10:24:08 [+0100], Julien Grall wrote: > diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c > index b869e816e96a..119414a2f59c 100644 > --- a/kernel/time/hrtimer.c > +++ b/kernel/time/hrtimer.c > @@ -934,7 +934,7 @@ void hrtimer_grab_expiry_lock(const struct hrtimer *timer) > { > struct hrtimer_clock_base *base = READ_ONCE(timer->base); > > - if (base && base->cpu_base) { > + if (timer->is_soft && base && base->cpu_base) { > spin_lock(&base->cpu_base->softirq_expiry_lock); > spin_unlock(&base->cpu_base->softirq_expiry_lock); > } right, much simpler. Sebastian
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c index b869e816e96a..119414a2f59c 100644 --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -934,7 +934,7 @@ void hrtimer_grab_expiry_lock(const struct hrtimer *timer) { struct hrtimer_clock_base *base = READ_ONCE(timer->base); - if (base && base->cpu_base) { + if (timer->is_soft && base && base->cpu_base) { spin_lock(&base->cpu_base->softirq_expiry_lock); spin_unlock(&base->cpu_base->softirq_expiry_lock); }
There are no guarantee the hrtimer_cancel() will be called on the same CPU as the non-soft hrtimer is running on so the following scenario can happen. CPU0 | CPU1 | | hrtimer_interrupt() | raw_spin_lock_irqsave(&cpu_save->lock) hrtimer_cancel() | __run_hrtimer_run_queues() hrtimer_try_to_cancel() | __run_hrtimer() lock_hrtimer_base() | base->running = timer; | raw_spin_unlock_irqrestore(&cpu_save->lock) raw_spin_lock_irqsave(cpu_base->lock) | fn(timer); hrtimer_callback_running() | hrtimer_callback_running() will be returning true as the callback is running somewhere else. This means hrtimer_try_to_cancel() would return -1. Therefore hrtimer_grab_expiry_lock() would be called. non-soft hrtimer may be used when the timer needs to be manipulated from a non-preemptible context. This is for instance the case of KVM Arm timers. The following splat can be seen in the log: [ 157.449545] 000: BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:968 [ 157.449569] 000: in_atomic(): 1, irqs_disabled(): 0, pid: 990, name: kvm-vcpu-1 [ 157.449579] 000: 2 locks held by kvm-vcpu-1/990: [ 157.449592] 000: #0: 00000000c2fc8217 (&vcpu->mutex){+.+.}, at: kvm_vcpu_ioctl+0x70/0xae0 [ 157.449638] 000: #1: 0000000096863801 (&cpu_base->softirq_expiry_lock){+.+.}, at: hrtimer_grab_expiry_lock+0x24/0x40 [ 157.449677] 000: Preemption disabled at: [ 157.449679] 000: [<ffff0000111a4538>] schedule+0x30/0xd8 [ 157.449702] 000: CPU: 0 PID: 990 Comm: kvm-vcpu-1 Tainted: G W 5.2.0-rt1-00001-gd368139e892f #104 [ 157.449712] 000: Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Jan 23 2017 [ 157.449718] 000: Call trace: [ 157.449722] 000: dump_backtrace+0x0/0x130 [ 157.449730] 000: show_stack+0x14/0x20 [ 157.449738] 000: dump_stack+0xbc/0x104 [ 157.449747] 000: ___might_sleep+0x198/0x238 [ 157.449756] 000: rt_spin_lock+0x5c/0x70 [ 157.449765] 000: hrtimer_grab_expiry_lock+0x24/0x40 [ 157.449773] 000: hrtimer_cancel+0x1c/0x38 [ 157.449780] 000: kvm_timer_vcpu_load+0x78/0x3e0 An hrtimer is always either running in softirq or not. This cannot be changed after it is instantiated. So we can rely on timer->is_soft for checking whether the lock can be grabbed. Signed-off-by: Julien Grall <julien.grall@arm.com> --- kernel/time/hrtimer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 2.11.0