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    perf: Remove WARN_ON_ONCE() check in __perf_event_enable() for valid scenario · 06f41796
    Jiri Olsa 提交于
    The '!ctx->is_active' check has a valid scenario, so
    there's no need for the warning.
    
    The reason is that there's a time window between the
    'ctx->is_active' check in the perf_event_enable() function
    and the __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 the warning below.
    
    So remove the WARN_ON_ONCE() check and add comments to
    explain it all.
    
    This addresses the following warning reported by Vince Weaver:
    
    [  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: NVince Weaver <vincent.weaver@maine.edu>
    Signed-off-by: NJiri Olsa <jolsa@redhat.com>
    Suggested-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: <stable@kernel.org>
    Signed-off-by: NPeter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/1373384651-6109-2-git-send-email-jolsa@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
    06f41796
core.c 182.1 KB