linux-kernel - Re: [syzbot] [kernel?] WARNING in posixtimer_send

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Message-Id: <20241115232117.3774-1-hdanton@sina.com>
Date: Sat, 16 Nov 2024 07:21:17 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+852e935b899bde73626e@...kaller.appspotmail.com>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com,
	tglx@...utronix.de
Subject: Re: [syzbot] [kernel?] WARNING in posixtimer_send_sigqueue

On Fri, 15 Nov 2024 21:55:02 +0100 Frederic Weisbecker <frederic@...nel.org>
> 
> Can you test on git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
> timers/core instead?

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git  timers/core

--- x/kernel/signal.c
+++ y/kernel/signal.c
@@ -2003,9 +2003,15 @@ void posixtimer_send_sigqueue(struct k_i
 	if (!prepare_signal(sig, t, false)) {
 		result = TRACE_SIGNAL_IGNORED;
 
-		/* Paranoia check. Try to survive. */
-		if (WARN_ON_ONCE(!list_empty(&q->list)))
+		if (!list_empty(&q->list)) {
+			/*
+			 * If task group is exiting with the signal already pending,
+			 * wait for __exit_signal() to do its job. Otherwise if
+			 * ignored, it's not supposed to be queued. Try to survive.
+			 */
+			WARN_ON_ONCE(!(t->signal->flags & SIGNAL_GROUP_EXIT));
 			goto out;
+		}
 
 		/* Periodic timers with SIG_IGN are queued on the ignored list */
 		if (tmr->it_sig_periodic) {
--