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    Subject[PATCH 3.5 59/62] perf: Fix hotplug splat
    Date
    3.5.7.32 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Peter Zijlstra <peterz@infradead.org>

    commit e3703f8cdfcf39c25c4338c3ad8e68891cca3731 upstream.

    Drew Richardson reported that he could make the kernel go *boom* when hotplugging
    while having perf events active.

    It turned out that when you have a group event, the code in
    __perf_event_exit_context() fails to remove the group siblings from
    the context.

    We then proceed with destroying and freeing the event, and when you
    re-plug the CPU and try and add another event to that CPU, things go
    *boom* because you've still got dead entries there.

    Reported-by: Drew Richardson <drew.richardson@arm.com>
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Cc: Will Deacon <will.deacon@arm.com>
    Link: http://lkml.kernel.org/n/tip-k6v5wundvusvcseqj1si0oz0@git.kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    kernel/events/core.c | 12 ++++++------
    1 file changed, 6 insertions(+), 6 deletions(-)

    diff --git a/kernel/events/core.c b/kernel/events/core.c
    index 3ea14c1..9e13b2d 100644
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -7148,14 +7148,14 @@ static void perf_pmu_rotate_stop(struct pmu *pmu)
    static void __perf_event_exit_context(void *__info)
    {
    struct perf_event_context *ctx = __info;
    - struct perf_event *event, *tmp;
    + struct perf_event *event;

    perf_pmu_rotate_stop(ctx->pmu);

    - list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry)
    - __perf_remove_from_context(event);
    - list_for_each_entry_safe(event, tmp, &ctx->flexible_groups, group_entry)
    + rcu_read_lock();
    + list_for_each_entry_rcu(event, &ctx->event_list, event_entry)
    __perf_remove_from_context(event);
    + rcu_read_unlock();
    }

    static void perf_event_exit_cpu_context(int cpu)
    @@ -7179,11 +7179,11 @@ static void perf_event_exit_cpu(int cpu)
    {
    struct swevent_htable *swhash = &per_cpu(swevent_htable, cpu);

    + perf_event_exit_cpu_context(cpu);
    +
    mutex_lock(&swhash->hlist_mutex);
    swevent_hlist_release(swhash);
    mutex_unlock(&swhash->hlist_mutex);
    -
    - perf_event_exit_cpu_context(cpu);
    }
    #else
    static inline void perf_event_exit_cpu(int cpu) { }
    --
    1.9.0


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