From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 6 Jul 2022 12:20:59 -0700
Subject: signal handling: don't use BUG_ON() for debugging
Git-commit: a382f8fee42ca10c9bfce0d2352d4153f931f5dc
Patch-mainline: v5.19-rc6
References: bsc#1210439

These are indeed "should not happen" situations, but it turns out recent
changes made the 'task_is_stopped_or_trace()' case trigger (fix for that
exists, is pending more testing), and the BUG_ON() makes it
unnecessarily hard to actually debug for no good reason.

It's been that way for a long time, but let's make it clear: BUG_ON() is
not good for debugging, and should never be used in situations where you
could just say "this shouldn't happen, but we can continue".

Use WARN_ON_ONCE() instead to make sure it gets logged, and then just
continue running.  Instead of making the system basically unusuable
because you crashed the machine while potentially holding some very core
locks (eg this function is commonly called while holding 'tasklist_lock'
for writing).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Michal Koutný <mkoutny@suse.com>
---
 kernel/signal.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index edb1dc9b00dc..6f86fda5e432 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2029,12 +2029,12 @@ bool do_notify_parent(struct task_struct *tsk, int sig)
 	bool autoreap = false;
 	u64 utime, stime;
 
-	BUG_ON(sig == -1);
+	WARN_ON_ONCE(sig == -1);
 
- 	/* do_notify_parent_cldstop should have been called instead.  */
- 	BUG_ON(task_is_stopped_or_traced(tsk));
+	/* do_notify_parent_cldstop should have been called instead.  */
+	WARN_ON_ONCE(task_is_stopped_or_traced(tsk));
 
-	BUG_ON(!tsk->ptrace &&
+	WARN_ON_ONCE(!tsk->ptrace &&
 	       (tsk->group_leader != tsk || !thread_group_empty(tsk)));
 
 	/* Wake up all pidfd waiters */