>
> 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.
The task_ctx_data will be checked before use. So it wouldn't crash the
system if it's NULL.
The problem is that LBR stack info will not be save/store on context switch
anymore. The user probably get wrong call stack information.
May I know why you want to do that?
Thanks,
Kan
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