[syzbot] [perf?] WARNING in perf_pending_task

[syzbot]

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+2fe61c...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 0 PID: 5309 at kernel/events/core.c:7211 perf_sigtrap kernel/events/core.c:7211 [inline]
WARNING: CPU: 0 PID: 5309 at kernel/events/core.c:7211 perf_pending_task+0x319/0x400 kernel/events/core.c:7325
Modules linked in:
CPU: 0 UID: 0 PID: 5309 Comm: syz-executor122 Not tainted 6.16.0-rc2-syzkaller-00378-gb67ec639010f #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:perf_sigtrap kernel/events/core.c:7211 [inline]
RIP: 0010:perf_pending_task+0x319/0x400 kernel/events/core.c:7325
Code: 85 8f 00 00 00 41 fe 4d 00 eb 05 e8 21 4f cd ff 48 83 c4 18 5b 41 5c 41 5d 41 5e 41 5f 5d e9 4e 34 76 09 cc e8 08 4f cd ff 90 <0f> 0b 90 41 80 3c 1c 00 0f 85 02 ff ff ff e9 05 ff ff ff 44 89 e1
RSP: 0018:ffffc9000d41f9d0 EFLAGS: 00010293
RAX: ffffffff81f2fe18 RBX: dffffc0000000000 RCX: ffff888032cbc880
RDX: 0000000000000000 RSI: 0000000074971a36 RDI: 0000000000000000
RBP: 0000000074971a36 R08: ffffffff8fa10af7 R09: 1ffffffff1f4215e
R10: dffffc0000000000 R11: ffffffff81f2fb00 R12: 1ffff110035f390f
R13: ffff888032cbc880 R14: ffff88801af9cad8 R15: ffff88801af9c878
FS: 0000000000000000(0000) GS:ffff88808d251000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000018 CR3: 000000000df38000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
task_work_run+0x1d1/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x6b5/0x22e0 kernel/exit.c:964
do_group_exit+0x21c/0x2d0 kernel/exit.c:1105
get_signal+0x1286/0x1340 kernel/signal.c:3034
arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:111
exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9ae420dab9
Code: Unable to access opcode bytes at 0x7f9ae420da8f.
RSP: 002b:00007ffd20a313c8 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: 0000000000000003 RBX: 0000000000000000 RCX: 00007f9ae420dab9
RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 0000200000000000
RBP: 00007f9ae42805f0 R08: 0000000000000000 R09: 0000000000000006
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000001
R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001
</TASK>


---
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[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,

[syzbot]

For archival purposes, forwarding an incoming command email to
syzkall...@googlegroups.com.

***

Subject: [PATCH] perf/core: Fix WARN in perf_sigtrap()
Author: penguin...@i-love.sakura.ne.jp

Since commit 4f6fc7821283 ("perf: Fix sample vs do_exit()") has moved
perf_event_exit_task() call from after exit_task_work() to before
exit_task_work(), task_work_add() from perf_event_exit_task() now returns
0 than -ESRCH, despite perf_event_exit_task_context() updates ctx->task
to TASK_TOMBSTONE. As a result, event->ctx->task == current assumption
no longer holds.

Reported-by: syzbot <syzbot+2fe61c...@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=2fe61cb2a86066be6985
Fixes: 4f6fc7821283 ("perf: Fix sample vs do_exit()")
Signed-off-by: Tetsuo Handa <penguin...@I-love.SAKURA.ne.jp>
---
#syz test

kernel/events/core.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7281230044d0..489f42defe3c 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7208,7 +7208,8 @@ static void perf_sigtrap(struct perf_event *event)

* 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 (WARN_ON_ONCE(event->ctx->task != current))

+ if (WARN_ON_ONCE(event->ctx->task != current &&
+ event->ctx->task != TASK_TOMBSTONE))
return;

/*
--
2.50.0

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+2fe61c...@syzkaller.appspotmail.com
Tested-by: syzbot+2fe61c...@syzkaller.appspotmail.com

Tested on:

commit: a79a588f Merge tag 'pm-6.16-rc5' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13691c8c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a6dba31fc9bb876c
dashboard link: https://syzkaller.appspot.com/bug?extid=2fe61cb2a86066be6985
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch: https://syzkaller.appspot.com/x/patch.diff?x=157a2582580000

Note: testing is done by a robot and is best-effort only.