On Tue, Jul 09, 2013 at 05:44:11PM +0200, Jiri Olsa wrote: > The '!ctx->is_active' check has a valid scenario, so > there's no need for the WARN macro. > > The reason is that there's a time window between > 'ctx->is_active' check in perf_event_enable function > and __perf_event_enable function having: > - IRQs on > - ctx->lock unlocked > > where the task could be killed and 'ctx' deactivated by > perf_event_exit_task, ending up with WARN below. > > Removing the WARN_ON_ONCE check. > > [ 324.983534] ------------[ cut here ]------------ > [ 324.984420] WARNING: at kernel/events/core.c:1953 > __perf_event_enable+0x187/0x190() > [ 324.984420] Modules linked in: > [ 324.984420] CPU: 19 PID: 2715 Comm: nmi_bug_snb Not tainted 3.10.0+ #246 > [ 324.984420] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010 > [ 324.984420] 0000000000000009 ffff88043fce3ec8 ffffffff8160ea0b > ffff88043fce3f00 > [ 324.984420] ffffffff81080ff0 ffff8802314fdc00 ffff880231a8f800 > ffff88043fcf7860 > [ 324.984420] 0000000000000286 ffff880231a8f800 ffff88043fce3f10 > ffffffff8108103a > [ 324.984420] Call Trace: > [ 324.984420] <IRQ> [<ffffffff8160ea0b>] dump_stack+0x19/0x1b > [ 324.984420] [<ffffffff81080ff0>] warn_slowpath_common+0x70/0xa0 > [ 324.984420] [<ffffffff8108103a>] warn_slowpath_null+0x1a/0x20 > [ 324.984420] [<ffffffff81134437>] __perf_event_enable+0x187/0x190 > [ 324.984420] [<ffffffff81130030>] remote_function+0x40/0x50 > [ 324.984420] [<ffffffff810e51de>] > generic_smp_call_function_single_interrupt+0xbe/0x130 > [ 324.984420] [<ffffffff81066a47>] > smp_call_function_single_interrupt+0x27/0x40 > [ 324.984420] [<ffffffff8161fd2f>] call_function_single_interrupt+0x6f/0x80 > [ 324.984420] <EOI> [<ffffffff816161a1>] ? > _raw_spin_unlock_irqrestore+0x41/0x70 > [ 324.984420] [<ffffffff8113799d>] perf_event_exit_task+0x14d/0x210 > [ 324.984420] [<ffffffff810acd04>] ? switch_task_namespaces+0x24/0x60 > [ 324.984420] [<ffffffff81086946>] do_exit+0x2b6/0xa40 > [ 324.984420] [<ffffffff8161615c>] ? _raw_spin_unlock_irq+0x2c/0x30 > [ 324.984420] [<ffffffff81087279>] do_group_exit+0x49/0xc0 > [ 324.984420] [<ffffffff81096854>] get_signal_to_deliver+0x254/0x620 > [ 324.984420] [<ffffffff81043057>] do_signal+0x57/0x5a0 > [ 324.984420] [<ffffffff8161a164>] ? __do_page_fault+0x2a4/0x4e0 > [ 324.984420] [<ffffffff8161665c>] ? retint_restore_args+0xe/0xe > [ 324.984420] [<ffffffff816166cd>] ? retint_signal+0x11/0x84 > [ 324.984420] [<ffffffff81043605>] do_notify_resume+0x65/0x80 > [ 324.984420] [<ffffffff81616702>] retint_signal+0x46/0x84 > [ 324.984420] ---[ end trace 442ec2f04db3771a ]--- > > Reported-by: Vince Weaver <vincent.wea...@maine.edu> > Signed-off-by: Jiri Olsa <jo...@redhat.com>
Suggested-by: Peter Zijlstra <a.p.zijls...@chello.nl> > Cc: Corey Ashford <cjash...@linux.vnet.ibm.com> > Cc: Frederic Weisbecker <fweis...@gmail.com> > Cc: Ingo Molnar <mi...@elte.hu> > Cc: Namhyung Kim <namhy...@kernel.org> > Cc: Paul Mackerras <pau...@samba.org> > Cc: Peter Zijlstra <a.p.zijls...@chello.nl> > Cc: Arnaldo Carvalho de Melo <a...@redhat.com> > Cc: Vince Weaver <vincent.wea...@maine.edu> > --- > kernel/events/core.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 446ec3d..eba8fb5 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -1963,7 +1963,16 @@ static int __perf_event_enable(void *info) > struct perf_cpu_context *cpuctx = __get_cpu_context(ctx); > int err; > > - if (WARN_ON_ONCE(!ctx->is_active)) > + /* > + * There's a time window between 'ctx->is_active' check > + * in perf_event_enable function and this place having: > + * - IRQs on > + * - ctx->lock unlocked > + * > + * where the task could be killed and 'ctx' deactivated > + * by perf_event_exit_task. > + */ > + if (!ctx->is_active) > return -EINVAL; > > raw_spin_lock(&ctx->lock); > -- > 1.7.11.7 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
