[v5.15] INFO: rcu detected stall in inotify_add_watch

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: de9476bb4f1b Linux 5.15.192
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=131b1d62580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4aee9f779ad20a6a
dashboard link: https://syzkaller.appspot.com/bug?extid=ca2223ff80b82ce4d555
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f98a0d0b1f65/disk-de9476bb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/690c073325bd/vmlinux-de9476bb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/771a90764b1a/bzImage-de9476bb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ca2223...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P9/1:b..l P4302/1:b..l
(detected by 1, t=10503 jiffies, g=10381, q=40)
task:udevd state:R running task stack:23296 pid: 4302 ppid: 3561 flags:0x00004002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11bb/0x4390 kernel/sched/core.c:6395
preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6799
irqentry_exit+0x63/0x70 kernel/entry/common.c:432
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:seqcount_lockdep_reader_access+0x17a/0x1c0 include/linux/seqlock.h:106
Code: ff 4d 85 ed 75 16 e8 d5 48 ad ff eb 15 e8 ce 48 ad ff e8 49 6c de 07 4d 85 ed 74 ea e8 bf 48 ad ff fb 48 c7 04 24 0e 36 e0 45 <4b> c7 04 27 00 00 00 00 66 43 c7 44 27 09 00 00 43 c6 44 27 0b 00
RSP: 0018:ffffc900030cf860 EFLAGS: 00000293
RAX: ffffffff81ca8221 RBX: 0000000000000000 RCX: ffff88807de7d940
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900030cf910 R08: dffffc0000000000 R09: fffffbfff1ad31e6
R10: fffffbfff1ad31e6 R11: 1ffffffff1ad31e5 R12: dffffc0000000000
R13: 0000000000000200 R14: ffffffff81ca9092 R15: 1ffff92000619f0c
__follow_mount_rcu fs/namei.c:1457 [inline]
handle_mounts fs/namei.c:1490 [inline]
step_into+0x642/0xd00 fs/namei.c:1806
link_path_walk+0x662/0xd40 fs/namei.c:-1
path_lookupat+0x9d/0x440 fs/namei.c:2454
filename_lookup+0x1e2/0x4f0 fs/namei.c:2484
user_path_at_empty+0x40/0x190 fs/namei.c:2883
user_path_at include/linux/namei.h:57 [inline]
inotify_find_inode fs/notify/inotify/inotify_user.c:370 [inline]
__do_sys_inotify_add_watch fs/notify/inotify/inotify_user.c:769 [inline]
__se_sys_inotify_add_watch+0x18e/0xea0 fs/notify/inotify/inotify_user.c:722
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fcb5ab309a7
RSP: 002b:00007ffeedcae898 EFLAGS: 00000206 ORIG_RAX: 00000000000000fe
RAX: ffffffffffffffda RBX: 0000558d440bfb20 RCX: 00007fcb5ab309a7
RDX: 0000000000000008 RSI: 0000558d440bd660 RDI: 0000000000000007
RBP: 0000558d440ad910 R08: 00000000000001d0 R09: 0000000000000003
R10: 0000000000000000 R11: 0000000000000206 R12: 0000558d440bfb20
R13: 0000558d440c5410 R14: 0000000000000008 R15: 0000558d440bfb20
</TASK>
task:kworker/u4:0 state:R running task stack:24968 pid: 9 ppid: 2 flags:0x00004000
Workqueue: bat_events batadv_nc_worker
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11bb/0x4390 kernel/sched/core.c:6395
preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6799
irqentry_exit+0x63/0x70 kernel/entry/common.c:432
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:lock_acquire+0x1f2/0x3f0 kernel/locking/lockdep.c:5627
Code: 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 0f 85 f6 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 66 43 c7 44 3d 09 00 00 43 c6 44 3d 0b
RSP: 0018:ffffc90000ce7aa0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: d542ea1252e0d800
RDX: 0000000000000000 RSI: ffffffff8a0b28c0 RDI: ffffffff8a59a240
RBP: ffffc90000ce7bc0 R08: dffffc0000000000 R09: fffffbfff1ff7619
R10: fffffbfff1ff7619 R11: 1ffffffff1ff7618 R12: ffffffff8c11c460
R13: 1ffff9200019cf60 R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:312
rcu_read_lock include/linux/rcupdate.h:739 [inline]
batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:412 [inline]
batadv_nc_worker+0xc9/0x5c0 net/batman-adv/network-coding.c:723
process_one_work+0x863/0x1000 kernel/workqueue.c:2310
worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>


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