| Message ID | 1446243386-26582-1-git-send-email-yang.shi@linaro.org |
|---|---|
| State | Accepted |
| Commit | ac00881f922106b45e934dc6988fa9c1ec542d71 |
| Headers | show |
On 11/2/2015 12:59 AM, Thomas Gleixner wrote: > On Sun, 1 Nov 2015, Alexei Starovoitov wrote: >> On Sat, Oct 31, 2015 at 09:47:36AM -0400, Steven Rostedt wrote: >>> On Fri, 30 Oct 2015 17:03:58 -0700 >>> Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote: >>> >>>> On Fri, Oct 30, 2015 at 03:16:26PM -0700, Yang Shi wrote: >>>>> When running bpf samples on rt kernel, it reports the below warning: >>>>> >>>>> BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917 >>>>> in_atomic(): 1, irqs_disabled(): 128, pid: 477, name: ping >>>>> Preemption disabled at:[<ffff80000017db58>] kprobe_perf_func+0x30/0x228 >>>> ... >>>>> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c >>>>> index 83c209d..972b76b 100644 >>>>> --- a/kernel/bpf/hashtab.c >>>>> +++ b/kernel/bpf/hashtab.c >>>>> @@ -17,7 +17,7 @@ >>>>> struct bpf_htab { >>>>> struct bpf_map map; >>>>> struct hlist_head *buckets; >>>>> - spinlock_t lock; >>>>> + raw_spinlock_t lock; >>>> >>>> How do we address such things in general? >>>> I bet there are tons of places around the kernel that >>>> call spin_lock from atomic. >>>> I'd hate to lose the benefits of lockdep of non-raw spin_lock >>>> just to make rt happy. >>> >>> You wont lose any benefits of lockdep. Lockdep still checks >>> raw_spin_lock(). The only difference between raw_spin_lock and >>> spin_lock is that in -rt spin_lock turns into an rt_mutex() and >>> raw_spin_lock stays a spin lock. >> >> I see. The patch makes sense then. >> Would be good to document this peculiarity of spin_lock. > > I'm working on a document. Thanks Steven and Thomas for your elaboration and comment. Yang > > Thanks, > > tglx > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On 11/2/2015 9:24 AM, Steven Rostedt wrote: > On Mon, 02 Nov 2015 09:12:29 -0800 > "Shi, Yang" <yang.shi@linaro.org> wrote: > >> Yes, it is common practice for converting sleepable spin lock to raw >> spin lock in -rt to avoid scheduling in atomic context bug. > > Note, in a lot of cases we don't just convert spin_locks to raw because > of atomic context. There's times we need to change the design where the > lock is not taken in atomic context (switching preempt_disable() to a > local_lock() for example). Yes, definitely. Understood. Thanks, Yang > > But bpf is much like ftrace and kprobes where they can be taken almost > anywhere, and the do indeed need to be raw. > > -- Steve > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c index 83c209d..972b76b 100644 --- a/kernel/bpf/hashtab.c +++ b/kernel/bpf/hashtab.c @@ -17,7 +17,7 @@ struct bpf_htab { struct bpf_map map; struct hlist_head *buckets; - spinlock_t lock; + raw_spinlock_t lock; u32 count; /* number of elements in this hashtable */ u32 n_buckets; /* number of hash buckets */ u32 elem_size; /* size of each element in bytes */ @@ -82,7 +82,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) for (i = 0; i < htab->n_buckets; i++) INIT_HLIST_HEAD(&htab->buckets[i]); - spin_lock_init(&htab->lock); + raw_spin_lock_init(&htab->lock); htab->count = 0; htab->elem_size = sizeof(struct htab_elem) + @@ -230,7 +230,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, l_new->hash = htab_map_hash(l_new->key, key_size); /* bpf_map_update_elem() can be called in_irq() */ - spin_lock_irqsave(&htab->lock, flags); + raw_spin_lock_irqsave(&htab->lock, flags); head = select_bucket(htab, l_new->hash); @@ -266,11 +266,11 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, } else { htab->count++; } - spin_unlock_irqrestore(&htab->lock, flags); + raw_spin_unlock_irqrestore(&htab->lock, flags); return 0; err: - spin_unlock_irqrestore(&htab->lock, flags); + raw_spin_unlock_irqrestore(&htab->lock, flags); kfree(l_new); return ret; } @@ -291,7 +291,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) hash = htab_map_hash(key, key_size); - spin_lock_irqsave(&htab->lock, flags); + raw_spin_lock_irqsave(&htab->lock, flags); head = select_bucket(htab, hash); @@ -304,7 +304,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) ret = 0; } - spin_unlock_irqrestore(&htab->lock, flags); + raw_spin_unlock_irqrestore(&htab->lock, flags); return ret; }
When running bpf samples on rt kernel, it reports the below warning: BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917 in_atomic(): 1, irqs_disabled(): 128, pid: 477, name: ping Preemption disabled at:[<ffff80000017db58>] kprobe_perf_func+0x30/0x228 CPU: 3 PID: 477 Comm: ping Not tainted 4.1.10-rt8 #4 Hardware name: Freescale Layerscape 2085a RDB Board (DT) Call trace: [<ffff80000008a5b0>] dump_backtrace+0x0/0x128 [<ffff80000008a6f8>] show_stack+0x20/0x30 [<ffff8000007da90c>] dump_stack+0x7c/0xa0 [<ffff8000000e4830>] ___might_sleep+0x188/0x1a0 [<ffff8000007e2200>] rt_spin_lock+0x28/0x40 [<ffff80000018bf9c>] htab_map_update_elem+0x124/0x320 [<ffff80000018c718>] bpf_map_update_elem+0x40/0x58 [<ffff800000187658>] __bpf_prog_run+0xd48/0x1640 [<ffff80000017ca6c>] trace_call_bpf+0x8c/0x100 [<ffff80000017db58>] kprobe_perf_func+0x30/0x228 [<ffff80000017dd84>] kprobe_dispatcher+0x34/0x58 [<ffff8000007e399c>] kprobe_handler+0x114/0x250 [<ffff8000007e3bf4>] kprobe_breakpoint_handler+0x1c/0x30 [<ffff800000085b80>] brk_handler+0x88/0x98 [<ffff8000000822f0>] do_debug_exception+0x50/0xb8 Exception stack(0xffff808349687460 to 0xffff808349687580) 7460: 4ca2b600 ffff8083 4a3a7000 ffff8083 49687620 ffff8083 0069c5f8 ffff8000 7480: 00000001 00000000 007e0628 ffff8000 496874b0 ffff8083 007e1de8 ffff8000 74a0: 496874d0 ffff8083 0008e04c ffff8000 00000001 00000000 4ca2b600 ffff8083 74c0: 00ba2e80 ffff8000 49687528 ffff8083 49687510 ffff8083 000e5c70 ffff8000 74e0: 00c22348 ffff8000 00000000 ffff8083 49687510 ffff8083 000e5c74 ffff8000 7500: 4ca2b600 ffff8083 49401800 ffff8083 00000001 00000000 00000000 00000000 7520: 496874d0 ffff8083 00000000 00000000 00000000 00000000 00000000 00000000 7540: 2f2e2d2c 33323130 00000000 00000000 4c944500 ffff8083 00000000 00000000 7560: 00000000 00000000 008751e0 ffff8000 00000001 00000000 124e2d1d 00107b77 Convert hashtab lock to raw lock to avoid such warning. Signed-off-by: Yang Shi <yang.shi@linaro.org> --- This patch is applicable to mainline kernel too. kernel/bpf/hashtab.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) -- 2.0.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/