lkml.org 
[lkml]   [2016]   [Feb]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[tip:perf/urgent] perf: Cure event->pending_disable race
    Commit-ID:  28a967c3a2f99fa3b5f762f25cb2a319d933571b
    Gitweb: http://git.kernel.org/tip/28a967c3a2f99fa3b5f762f25cb2a319d933571b
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Wed, 24 Feb 2016 18:45:46 +0100
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Thu, 25 Feb 2016 08:42:34 +0100

    perf: Cure event->pending_disable race

    Because event_sched_out() checks event->pending_disable _before_
    actually disabling the event, it can happen that the event fires after
    it checks but before it gets disabled.

    This would leave event->pending_disable set and the queued irq_work
    will try and process it.

    However, if the event trigger was during schedule(), the event might
    have been de-scheduled by the time the irq_work runs, and
    perf_event_disable_local() will fail.

    Fix this by checking event->pending_disable _after_ we call
    event->pmu->del(). This depends on the latter being a compiler
    barrier, such that the compiler does not lift the load and re-creates
    the problem.

    Tested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: dvyukov@google.com
    Cc: eranian@google.com
    Cc: oleg@redhat.com
    Cc: panand@redhat.com
    Cc: sasha.levin@oracle.com
    Cc: vince@deater.net
    Link: http://lkml.kernel.org/r/20160224174948.040469884@infradead.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/events/core.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/kernel/events/core.c b/kernel/events/core.c
    index ea064ca..de14b67 100644
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -1696,14 +1696,14 @@ event_sched_out(struct perf_event *event,

    perf_pmu_disable(event->pmu);

    + event->tstamp_stopped = tstamp;
    + event->pmu->del(event, 0);
    + event->oncpu = -1;
    event->state = PERF_EVENT_STATE_INACTIVE;
    if (event->pending_disable) {
    event->pending_disable = 0;
    event->state = PERF_EVENT_STATE_OFF;
    }
    - event->tstamp_stopped = tstamp;
    - event->pmu->del(event, 0);
    - event->oncpu = -1;

    if (!is_software_event(event))
    cpuctx->active_oncpu--;
    \
     
     \ /
      Last update: 2016-02-25 09:41    [W:6.830 / U:0.024 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site