[v6.1] INFO: rcu detected stall in flock

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1989cd3d56e2 Linux 6.1.167
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10bed01f980000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0605c5af04d7603
dashboard link: https://syzkaller.appspot.com/bug?extid=249f486cd608d194634d
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/814271465bd5/disk-1989cd3d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bd559379c491/vmlinux-1989cd3d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/063c12bf8ba7/bzImage-1989cd3d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+249f48...@syzkaller.appspotmail.com

bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
(detected by 1, t=10502 jiffies, g=29821, q=22 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10502 (4294977110-4294966608), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10502 jiffies! g29821 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt state:R running task stack:27608 pid:16 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5245 [inline]
__schedule+0x11d1/0x40e0 kernel/sched/core.c:6562
schedule+0xb9/0x180 kernel/sched/core.c:6638
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2168
rcu_gp_fqs_loop+0x303/0x1340 kernel/rcu/tree.c:1706
rcu_gp_kthread+0x99/0x3b0 kernel/rcu/tree.c:1905
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 7479 Comm: syz.5.830 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:__lock_acquire+0x3f6/0x7d10 kernel/locking/lockdep.c:4985
Code: 00 00 74 0f e8 2b 3a 6f 00 49 b8 00 00 00 00 00 fc ff df 48 8b 44 24 78 4c 89 70 08 49 89 c6 48 8d 78 10 48 89 f8 48 c1 e8 03 <42> 80 3c 00 00 74 0f e8 fe 39 6f 00 49 b8 00 00 00 00 00 fc ff df
RSP: 0018:ffffc900000079c0 EFLAGS: 00000806
RAX: 1ffff1100bf3351b RBX: ffffffff8cb46bc8 RCX: 1ffff1100bf3351d
RDX: 0000000000000049 RSI: 0000000000000000 RDI: ffff88805f99a8d8
RBP: ffffc90000007c10 R08: dffffc0000000000 R09: 0000000000000001
R10: dffffc0000000000 R11: fffffbfff1c3fbde R12: ffff88805f99a8c8
R13: 0000000000000000 R14: ffff88805f99a8c8 R15: 0000000000000049
FS: 00007fa93919e6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd0b63e9e80 CR3: 000000007bbc7000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5662
seqcount_lockdep_reader_access+0xcd/0x1d0 include/linux/seqlock.h:102
ktime_get+0x31/0x270 kernel/time/timekeeping.c:846
clockevents_program_event+0xe2/0x310 kernel/time/clockevents.c:326
hrtimer_interrupt+0x59d/0x9c0 kernel/time/hrtimer.c:1886
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1107 [inline]
__sysvec_apic_timer_interrupt+0x153/0x5a0 arch/x86/kernel/apic/apic.c:1124
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0x9b/0xc0 arch/x86/kernel/apic/apic.c:1118
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:lock_acquire+0x225/0x4a0 kernel/locking/lockdep.c:5666
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3d 04 f8 0f 85 f0 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 43 c7 44 3d 08 00 00 00 00 65 48 8b 04
RSP: 0018:ffffc90003de78e0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: e00a561ffbeb9e00
RDX: 0000000000000000 RSI: ffffffff8a8c2220 RDI: ffffffff8adf0d20
RBP: ffffc90003de79e8 R08: dffffc0000000000 R09: 1ffffffff215ee4a
R10: dffffc0000000000 R11: fffffbfff215ee4b R12: 0000000000000000
R13: 1ffff920007bcf28 R14: 0000000000000246 R15: dffffc0000000000
__fs_reclaim_acquire mm/page_alloc.c:4748 [inline]
fs_reclaim_acquire+0x6d/0x100 mm/page_alloc.c:4762
might_alloc include/linux/sched/mm.h:271 [inline]
slab_pre_alloc_hook+0x2a/0x310 mm/slab.h:710
slab_alloc_node mm/slub.c:3279 [inline]
slab_alloc mm/slub.c:3367 [inline]
__kmem_cache_alloc_lru mm/slub.c:3374 [inline]
kmem_cache_alloc+0x56/0x2f0 mm/slub.c:3383
kmem_cache_zalloc include/linux/slab.h:689 [inline]
locks_alloc_lock fs/locks.c:270 [inline]
flock_lock_inode+0x22a/0x1870 fs/locks.c:1023
flock_lock_inode_wait fs/locks.c:2034 [inline]
locks_lock_inode_wait+0x10a/0x480 fs/locks.c:2061
locks_lock_file_wait include/linux/fs.h:1365 [inline]
__do_sys_flock fs/locks.c:2131 [inline]
__se_sys_flock+0x47f/0x5a0 fs/locks.c:2085
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa93839c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa93919e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000049
RAX: ffffffffffffffda RBX: 00007fa938615fa0 RCX: 00007fa93839c799
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000004
RBP: 00007fa938432c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa938616038 R14: 00007fa938615fa0 R15: 00007fff561fd1a8
</TASK>


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