Re: [tip: perf/core] perf: Fix event_function_call() locking

[Peter Zijlstra]

On Tue, Aug 13, 2024 at 11:28:54AM -0700, Namhyung Kim wrote:

Duh, yeah.

> ---
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 9893ba5e98aa..85204c2376fa 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -298,13 +298,14 @@ static int event_function(void *info)
>  static void event_function_call(struct perf_event *event, event_f func, void *data)
>  {
>  	struct perf_event_context *ctx = event->ctx;
> -	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
> +	struct perf_cpu_context *cpuctx;
>  	struct task_struct *task = READ_ONCE(ctx->task); /* verified in event_function */
>  	struct event_function_struct efs = {
>  		.event = event,
>  		.func = func,
>  		.data = data,
>  	};
> +	unsigned long flags;
>  
>  	if (!event->parent) {
>  		/*
> @@ -327,22 +328,27 @@ static void event_function_call(struct perf_event *event, event_f func, void *da
>  	if (!task_function_call(task, event_function, &efs))
>  		return;
>  
> +	local_irq_save(flags);

This can just be local_irq_disable() though, seeing how the fingered
commit replaced raw_spin_lock_irq().

I'll queue the below...

---
Subject: perf: Really fix event_function_call() locking
From: Namhyung Kim <namhyung@xxxxxxxxxx>
Date: Tue Aug 13 22:55:11 CEST 2024

Commit 558abc7e3f89 ("perf: Fix event_function_call() locking") lost
IRQ disabling by mistake.

Fixes: 558abc7e3f89 ("perf: Fix event_function_call() locking")
Reported-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/events/core.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -298,8 +298,8 @@ static int event_function(void *info)
 static void event_function_call(struct perf_event *event, event_f func, void *data)
 {
 	struct perf_event_context *ctx = event->ctx;
-	struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
 	struct task_struct *task = READ_ONCE(ctx->task); /* verified in event_function */
+	struct perf_cpu_context *cpuctx;
 	struct event_function_struct efs = {
 		.event = event,
 		.func = func,
@@ -327,22 +327,25 @@ static void event_function_call(struct p
 	if (!task_function_call(task, event_function, &efs))
 		return;
 
+	local_irq_disable();
+	cpuctx = this_cpu_ptr(&perf_cpu_context);
 	perf_ctx_lock(cpuctx, ctx);
 	/*
 	 * Reload the task pointer, it might have been changed by
 	 * a concurrent perf_event_context_sched_out().
 	 */
 	task = ctx->task;
-	if (task == TASK_TOMBSTONE) {
-		perf_ctx_unlock(cpuctx, ctx);
-		return;
-	}
+	if (task == TASK_TOMBSTONE)
+		goto unlock;
 	if (ctx->is_active) {
 		perf_ctx_unlock(cpuctx, ctx);
+		local_irq_enable();
 		goto again;
 	}
 	func(event, NULL, ctx, data);
+unlock:
 	perf_ctx_unlock(cpuctx, ctx);
+	local_irq_enable();
 }
 
 /*