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    Subject[PATCH 3.16 288/328] perf/core: Fix perf_pmu_unregister() locking
    3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Peter Zijlstra <peterz@infradead.org>

    commit a9f9772114c8b07ae75bcb3654bd017461248095 upstream.

    When we unregister a PMU, we fail to serialize the @pmu_idr properly.
    Fix that by doing the entire thing under pmu_lock.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: 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: Stephane Eranian <eranian@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Vince Weaver <vincent.weaver@maine.edu>
    Fixes: 2e80a82a49c4 ("perf: Dynamic pmu types")
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    [bwh: Backported to 3.16:
    - Also remove "out" label in free_pmu_context()
    - Adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -6705,20 +6705,17 @@ static void free_pmu_context(struct pmu
    {
    struct pmu *i;

    - mutex_lock(&pmus_lock);
    /*
    * Like a real lame refcount.
    */
    list_for_each_entry(i, &pmus, entry) {
    if (i->pmu_cpu_context == pmu->pmu_cpu_context) {
    update_pmu_context(i, pmu);
    - goto out;
    + return;
    }
    }

    free_percpu(pmu->pmu_cpu_context);
    -out:
    - mutex_unlock(&pmus_lock);
    }
    static struct idr pmu_idr;

    @@ -6930,12 +6927,8 @@ EXPORT_SYMBOL_GPL(perf_pmu_register);

    void perf_pmu_unregister(struct pmu *pmu)
    {
    - int remove_device;
    -
    mutex_lock(&pmus_lock);
    - remove_device = pmu_bus_running;
    list_del_rcu(&pmu->entry);
    - mutex_unlock(&pmus_lock);

    /*
    * We dereference the pmu list under both SRCU and regular RCU, so
    @@ -6947,11 +6940,12 @@ void perf_pmu_unregister(struct pmu *pmu
    free_percpu(pmu->pmu_disable_count);
    if (pmu->type >= PERF_TYPE_MAX)
    idr_remove(&pmu_idr, pmu->type);
    - if (remove_device) {
    + if (pmu_bus_running) {
    device_del(pmu->dev);
    put_device(pmu->dev);
    }
    free_pmu_context(pmu);
    + mutex_unlock(&pmus_lock);
    }
    EXPORT_SYMBOL_GPL(perf_pmu_unregister);

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