Re: [syzbot] [perf?] WARNING in perf_pending_task

[Tetsuo Handa]

Hello.

I think that the cause of this problem is commit 4f6fc7821283 ("perf: Fix sample vs do_exit()"), for
syzbot found this problem in 5.15.186 and 6.1.142 where that was the only commit in kernel/events/ area
which has been backported between v5.15.185...v5.15.186 and v6.1.141...v6.1.142 .

Please have a look on this change. Maybe we need to swap WARN_ON_ONCE() and PF_EXITING checks?

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1f746469fda5..5a3a1331311f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7204,18 +7204,18 @@ void perf_event_wakeup(struct perf_event *event)
 static void perf_sigtrap(struct perf_event *event)
 {
 	/*
-	 * We'd expect this to only occur if the irq_work is delayed and either
-	 * ctx->task or current has changed in the meantime. This can be the
-	 * case on architectures that do not implement arch_irq_work_raise().
+	 * Both perf_pending_task() and perf_pending_irq() can race with the
+	 * task exiting.
 	 */
-	if (WARN_ON_ONCE(event->ctx->task != current))
+	if (current->flags & PF_EXITING)
 		return;
 
 	/*
-	 * Both perf_pending_task() and perf_pending_irq() can race with the
-	 * task exiting.
+	 * We'd expect this to only occur if the irq_work is delayed and either
+	 * ctx->task or current has changed in the meantime. This can be the
+	 * case on architectures that do not implement arch_irq_work_raise().
 	 */
-	if (current->flags & PF_EXITING)
+	if (WARN_ON_ONCE(event->ctx->task != current))
 		return;
 
 	send_sig_perf((void __user *)event->pending_addr,

On 2025/06/25 4:01, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    b67ec639010f Merge tag 'i2c-for-6.16-rc3' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17715b0c580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d11f52d3049c3790
> dashboard link: https://syzkaller.appspot.com/bug?extid=2fe61cb2a86066be6985
> compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10f15b0c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1692ab0c580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-b67ec639.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/3bcb2b262d02/vmlinux-b67ec639.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/f5d4477f1e2e/bzImage-b67ec639.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2fe61cb2a86066be6985@xxxxxxxxxxxxxxxxxxxxxxxxx