diff options
| -rw-r--r-- | kernel/events/core.c | 40 |
1 files changed, 20 insertions, 20 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 25edabd207de..614614821f00 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -64,8 +64,17 @@ static void remote_function(void *data) struct task_struct *p = tfc->p; if (p) { - tfc->ret = -EAGAIN; - if (task_cpu(p) != smp_processor_id() || !task_curr(p)) + /* -EAGAIN */ + if (task_cpu(p) != smp_processor_id()) + return; + + /* + * Now that we're on right CPU with IRQs disabled, we can test + * if we hit the right task without races. + */ + + tfc->ret = -ESRCH; /* No such (running) process */ + if (p != current) return; } @@ -92,13 +101,17 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info) .p = p, .func = func, .info = info, - .ret = -ESRCH, /* No such (running) process */ + .ret = -EAGAIN, }; + int ret; - if (task_curr(p)) - smp_call_function_single(task_cpu(p), remote_function, &data, 1); + do { + ret = smp_call_function_single(task_cpu(p), remote_function, &data, 1); + if (!ret) + ret = data.ret; + } while (ret == -EAGAIN); - return data.ret; + return ret; } /** @@ -169,19 +182,6 @@ static bool is_kernel_event(struct perf_event *event) * rely on ctx->is_active and therefore cannot use event_function_call(). * See perf_install_in_context(). * - * This is because we need a ctx->lock serialized variable (ctx->is_active) - * to reliably determine if a particular task/context is scheduled in. The - * task_curr() use in task_function_call() is racy in that a remote context - * switch is not a single atomic operation. - * - * As is, the situation is 'safe' because we set rq->curr before we do the - * actual context switch. This means that task_curr() will fail early, but - * we'll continue spinning on ctx->is_active until we've passed - * perf_event_task_sched_out(). - * - * Without this ctx->lock serialized variable we could have race where we find - * the task (and hence the context) would not be active while in fact they are. - * * If ctx->nr_events, then ctx->is_active and cpuctx->task_ctx are set. */ @@ -212,7 +212,7 @@ static int event_function(void *info) */ if (ctx->task) { if (ctx->task != current) { - ret = -EAGAIN; + ret = -ESRCH; goto unlock; } |