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    Subject[PATCH 3.16 287/328] perf/core: Protect PMU device removal with a 'pmu_bus_running' check, to fix CONFIG_DEBUG_TEST_DRIVER_REMOVE=y kernel panic
    3.16.62-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Jiri Olsa <jolsa@redhat.com>

    commit 0933840acf7b65d6d30a5b6089d882afea57aca3 upstream.

    CAI Qian reported a crash in the PMU uncore device removal code,
    enabled by the CONFIG_DEBUG_TEST_DRIVER_REMOVE=y option:

    https://marc.info/?l=linux-kernel&m=147688837328451

    The reason for the crash is that perf_pmu_unregister() tries to remove
    a PMU device which is not added at this point. We add PMU devices
    only after pmu_bus is registered, which happens in the
    perf_event_sysfs_init() call and sets the 'pmu_bus_running' flag.

    The fix is to get the 'pmu_bus_running' flag state at the point
    the PMU is taken out of the PMU list and remove the device
    later only if it's set.

    Reported-by: CAI Qian <caiqian@redhat.com>
    Tested-by: CAI Qian <caiqian@redhat.com>
    Signed-off-by: Jiri Olsa <jolsa@kernel.org>
    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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Kan Liang <kan.liang@intel.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Rob Herring <robh@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/20161020111011.GA13361@krava
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    [bwh: Backported to 3.16: no address filter attributes to clean up]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -6930,7 +6930,10 @@ 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);

    @@ -6944,8 +6947,10 @@ 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);
    - device_del(pmu->dev);
    - put_device(pmu->dev);
    + if (remove_device) {
    + device_del(pmu->dev);
    + put_device(pmu->dev);
    + }
    free_pmu_context(pmu);
    }
    EXPORT_SYMBOL_GPL(perf_pmu_unregister);
    \
     
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