signal handling: don't use BUG_ON() for debugging

[ Upstream commit f12e3c91b836133068f7880ac038f777e99f2608 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/signal.c b/kernel/signal.c
index 3f61367fd16857a7856ced7dc4b19f3283fb6c00..1f4293a107b491dff2c84d668a4e97b106190a4e 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1916,12 +1916,12 @@ 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 */