perf_counter: Check task on counter read IPI

[safe/jmp/linux-2.6] / kernel / perf_counter.c

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 534e20d..b8fe739 100644 (file)
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1503,10 +1503,21 @@ static void perf_counter_enable_on_exec(struct task_struct *task)
  */
 static void __perf_counter_read(void *info)
 {
+       struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_counter *counter = info;
        struct perf_counter_context *ctx = counter->ctx;
        unsigned long flags;
 
+       /*
+        * If this is a task context, we need to check whether it is
+        * the current task context of this cpu.  If not it has been
+        * scheduled out before the smp call arrived.  In that case
+        * counter->count would have been updated to a recent sample
+        * when the counter was scheduled out.
+        */
+       if (ctx->task && cpuctx->task_ctx != ctx)
+               return;
+
        local_irq_save(flags);
        if (ctx->is_active)
                update_context_time(ctx);