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    Subject[PATCH 3/7] perf_counter: sanitize context locking
    Ensure we're consistent with the context locks.

    context->mutex
    context->lock
    list_{add,del}_counter();

    so that either lock is sufficient to stabilize the context.

    LKML-Reference: <new-submission>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    kernel/perf_counter.c | 9 +++++++--
    1 file changed, 7 insertions(+), 2 deletions(-)

    Index: linux-2.6/kernel/perf_counter.c
    ===================================================================
    --- linux-2.6.orig/kernel/perf_counter.c
    +++ linux-2.6/kernel/perf_counter.c
    @@ -597,6 +597,8 @@ static void add_counter_to_ctx(struct pe

    /*
    * Cross CPU call to install and enable a performance counter
    + *
    + * Must be called with ctx->mutex held
    */
    static void __perf_install_in_context(void *info)
    {
    @@ -1496,13 +1498,13 @@ static void perf_counter_for_each_siblin
    struct perf_counter_context *ctx = counter->ctx;
    struct perf_counter *sibling;

    - spin_lock_irq(&ctx->lock);
    + mutex_lock(&ctx->mutex);
    counter = counter->group_leader;

    func(counter);
    list_for_each_entry(sibling, &counter->sibling_list, list_entry)
    func(sibling);
    - spin_unlock_irq(&ctx->lock);
    + mutex_unlock(&ctx->mutex);
    }

    static void perf_counter_for_each_child(struct perf_counter *counter,
    @@ -3414,7 +3416,10 @@ __perf_counter_exit_task(struct task_str
    struct perf_counter *parent_counter;

    update_counter_times(child_counter);
    +
    + spin_lock_irq(&child_ctx->lock);
    list_del_counter(child_counter, child_ctx);
    + spin_unlock_irq(&child_ctx->lock);

    parent_counter = child_counter->parent;
    /*
    --



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