Re: [PATCH] tracing/user_events: Run BPF program if attached

[Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>]

On Wed, May 17, 2023 at 12:36 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> .. this is the patch that I think should go on top of it to fix the
> misleading "safe" and the incorrect RCU walk.

Let's actually attach the patch too. Duh.

               Linus

 kernel/trace/trace_events_user.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index b2aecbfbbd24..054e28cc5ad4 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -439,7 +439,7 @@ static bool user_event_enabler_exists(struct user_event_mm *mm,
 	struct user_event_enabler *enabler;
 	struct user_event_enabler *next;
 
-	list_for_each_entry_safe(enabler, next, &mm->enablers, link) {
+	list_for_each_entry(enabler, next, &mm->enablers, link) {
 		if (enabler->addr == uaddr &&
 		    (enabler->values & ENABLE_VAL_BIT_MASK) == bit)
 			return true;
@@ -455,19 +455,19 @@ static void user_event_enabler_update(struct user_event *user)
 	struct user_event_mm *next;
 	int attempt;
 
+	lockdep_assert_held(&event_mutex);
+
 	while (mm) {
 		next = mm->next;
 		mmap_read_lock(mm->mm);
-		rcu_read_lock();
 
-		list_for_each_entry_rcu(enabler, &mm->enablers, link) {
+		list_for_each_entry(enabler, &mm->enablers, link) {
 			if (enabler->event == user) {
 				attempt = 0;
 				user_event_enabler_write(mm, enabler, true, &attempt);
 			}
 		}
 
-		rcu_read_unlock();
 		mmap_read_unlock(mm->mm);
 		user_event_mm_put(mm);
 		mm = next;