Re: [PATCH v13 09/14] unwind deferred: Use SRCU unwind_deferred_task_work()

[Peter Zijlstra]

On Mon, Jul 07, 2025 at 09:22:48PM -0400, Steven Rostedt wrote:

> @@ -143,6 +144,7 @@ static void unwind_deferred_task_work(struct callback_head *head)
>  	struct unwind_stacktrace trace;
>  	struct unwind_work *work;
>  	u64 cookie;
> +	int idx;
>  
>  	if (WARN_ON_ONCE(!local_read(&info->pending)))
>  		return;
> @@ -161,13 +163,15 @@ static void unwind_deferred_task_work(struct callback_head *head)
>  
>  	cookie = info->id.id;
>  
> -	guard(mutex)(&callback_mutex);
> -	list_for_each_entry(work, &callbacks, list) {
> +	idx = srcu_read_lock(&unwind_srcu);
> +	list_for_each_entry_srcu(work, &callbacks, list,
> +				 srcu_read_lock_held(&unwind_srcu)) {
>  		if (test_bit(work->bit, &info->unwind_mask)) {
>  			work->func(work, &trace, cookie);
>  			clear_bit(work->bit, &info->unwind_mask);
>  		}
>  	}
> +	srcu_read_unlock(&unwind_srcu, idx);
>  }

Please; something like so:

--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -524,4 +524,9 @@ DEFINE_LOCK_GUARD_1(srcu, struct srcu_st
 		    srcu_read_unlock(_T->lock, _T->idx),
 		    int idx)
 
+DEFINE_LOCK_GUARD_1(srcu_lite, struct srcu_struct,
+		    _T->idx = srcu_read_lock_lite(_T->lock),
+		    srcu_read_unlock_lite(_T->lock, _T->idx),
+		    int idx)
+
 #endif
--- a/kernel/unwind/deferred.c
+++ b/kernel/unwind/deferred.c
@@ -165,7 +165,7 @@ static void unwind_deferred_task_work(st
 
 	cookie = info->id.id;
 
-	guard(mutex)(&callback_mutex);
+	guard(srcu_lite)(&unwind_srcu);
 	list_for_each_entry(work, &callbacks, list) {
 		work->func(work, &trace, cookie);
 	}