[syzbot ci] Re: ext4: fix use-after-free in update_super_work when racing with umount

[syzbot ci]

syzbot ci has tested the following series

[v2] ext4: fix use-after-free in update_super_work when racing with umount
https://lore.kernel.org/all/20260319073651.79...@linux.dev
* [PATCH v2] ext4: fix use-after-free in update_super_work when racing with umount

and found the following issue:
WARNING in ext4_notify_error_sysfs

Full report is available here:
https://ci.syzbot.org/series/3b258c63-ea54-492a-ab47-c09e62612658

***

WARNING in ext4_notify_error_sysfs

tree: torvalds
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base: 0e4f8f1a3d081e834be5fd0a62bdb2554fadd307
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/8149e3c8-4cb9-4fa0-9bf5-3d6deda6899d/config
C repro: https://ci.syzbot.org/findings/6f6eafc6-a231-4909-9025-539fa10ffcfd/c_repro
syz repro: https://ci.syzbot.org/findings/6f6eafc6-a231-4909-9025-539fa10ffcfd/syz_repro

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(lock->magic != lock)
WARNING: kernel/locking/mutex.c:593 at __mutex_lock_common kernel/locking/mutex.c:593 [inline], CPU#1: kworker/1:4/5883
WARNING: kernel/locking/mutex.c:593 at __mutex_lock+0x10a4/0x1300 kernel/locking/mutex.c:776, CPU#1: kworker/1:4/5883
Modules linked in:
CPU: 1 UID: 0 PID: 5883 Comm: kworker/1:4 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: events update_super_work

RIP: 0010:__mutex_lock_common kernel/locking/mutex.c:593 [inline]
RIP: 0010:__mutex_lock+0x10ab/0x1300 kernel/locking/mutex.c:776
Code: 11 90 48 c1 e8 03 42 0f b6 04 28 84 c0 0f 85 33 02 00 00 83 3d d9 e1 61 04 00 75 13 48 8d 3d 1c f7 64 04 48 c7 c6 c0 e0 cc 8b <67> 48 0f b9 3a 90 e9 ac f0 ff ff 90 0f 0b 90 e9 73 f4 ff ff 90 0f
RSP: 0018:ffffc90004dcf900 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 1ffff920009b9f38 RCX: ffff888172d3d7c0
RDX: 0000000000000000 RSI: ffffffff8bcce0c0 RDI: ffffffff9014ec10
RBP: ffffc90004dcfaa8 R08: ffffffff9011d6c3 R09: 1ffffffff2023ad8
R10: dffffc0000000000 R11: fffffbfff2023ad9 R12: ffff888172218368
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8882a945d000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000562af42c7d40 CR3: 0000000111346000 CR4: 00000000000006f0
Call Trace:
<TASK>
ext4_notify_error_sysfs+0x23/0xa0 fs/ext4/sysfs.c:600
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
----------------
Code disassembly (best guess):
0: 11 90 48 c1 e8 03 adc %edx,0x3e8c148(%rax)
6: 42 0f b6 04 28 movzbl (%rax,%r13,1),%eax
b: 84 c0 test %al,%al
d: 0f 85 33 02 00 00 jne 0x246
13: 83 3d d9 e1 61 04 00 cmpl $0x0,0x461e1d9(%rip) # 0x461e1f3
1a: 75 13 jne 0x2f
1c: 48 8d 3d 1c f7 64 04 lea 0x464f71c(%rip),%rdi # 0x464f73f
23: 48 c7 c6 c0 e0 cc 8b mov $0xffffffff8bcce0c0,%rsi
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: 90 nop
30: e9 ac f0 ff ff jmp 0xfffff0e1
35: 90 nop
36: 0f 0b ud2
38: 90 nop
39: e9 73 f4 ff ff jmp 0xfffff4b1
3e: 90 nop
3f: 0f .byte 0xf


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syz...@syzkaller.appspotmail.com

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