Re: [tip:perf/core] perf: Add pmu specific data for perf task context

[Peter Zijlstra]

On Wed, Feb 18, 2015 at 09:15:06AM -0800, tip-bot for Yan, Zheng wrote:
> +find_get_context(struct pmu *pmu, struct task_struct *task,
> +             struct perf_event *event)
>  {
>       struct perf_event_context *ctx, *clone_ctx = NULL;
>       struct perf_cpu_context *cpuctx;
> +     void *task_ctx_data = NULL;
>       unsigned long flags;
>       int ctxn, err;
> +     int cpu = event->cpu;
>  
>       if (!task) {
>               /* Must be root to operate on a CPU event: */
> @@ -3342,11 +3354,24 @@ find_get_context(struct pmu *pmu, struct task_struct 
> *task, int cpu)
>       if (ctxn < 0)
>               goto errout;
>  
> +     if (event->attach_state & PERF_ATTACH_TASK_DATA) {
> +             task_ctx_data = kzalloc(pmu->task_ctx_size, GFP_KERNEL);
> +             if (!task_ctx_data) {
> +                     err = -ENOMEM;
> +                     goto errout;
> +             }
> +     }
> +
>  retry:
>       ctx = perf_lock_task_context(task, ctxn, &flags);
>       if (ctx) {
>               clone_ctx = unclone_ctx(ctx);
>               ++ctx->pin_count;
> +
> +             if (task_ctx_data && !ctx->task_ctx_data) {
> +                     ctx->task_ctx_data = task_ctx_data;
> +                     task_ctx_data = NULL;
> +             }
>               raw_spin_unlock_irqrestore(&ctx->lock, flags);
>  
>               if (clone_ctx)
> @@ -3357,6 +3382,11 @@ retry:
>               if (!ctx)
>                       goto errout;
>  
> +             if (task_ctx_data) {
> +                     ctx->task_ctx_data = task_ctx_data;
> +                     task_ctx_data = NULL;
> +             }
> +
>               err = 0;
>               mutex_lock(&task->perf_event_mutex);
>               /*
> @@ -3383,9 +3413,11 @@ retry:
>               }
>       }
>  
> +     kfree(task_ctx_data);
>       return ctx;
>  
>  errout:
> +     kfree(task_ctx_data);
>       return ERR_PTR(err);
>  }


diff --git a/kernel/events/core.c b/kernel/events/core.c
index 36babfd..97aa610 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3508,11 +3515,6 @@ retry:
                if (!ctx)
                        goto errout;
 
-               if (task_ctx_data) {
-                       ctx->task_ctx_data = task_ctx_data;
-                       task_ctx_data = NULL;
-               }
-
                err = 0;
                mutex_lock(&task->perf_event_mutex);
                /*
@@ -3526,6 +3528,10 @@ retry:
                else {
                        get_ctx(ctx);
                        ++ctx->pin_count;
+                       if (task_ctx_data) {
+                               ctx->task_ctx_data = task_ctx_data;
+                               task_ctx_data = NULL;
+                       }
                        rcu_assign_pointer(task->perf_event_ctxp[ctxn], ctx);
                }
                mutex_unlock(&task->perf_event_mutex);


Does that make sense? No point in setting task_ctx_data if we're going
to free the ctx and try again.
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