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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f2198ea7eb3e Linux 6.1.145
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=153e158c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=58bf4ec506e81fd3
dashboard link: https://syzkaller.appspot.com/bug?extid=b66dc5ff7710b6e22451
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0fa616ee00a2/disk-f2198ea7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8d9096e06b01/vmlinux-f2198ea7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/40ceb266796f/bzImage-f2198ea7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b66dc5...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P10207/1:b..l
(detected by 0, t=10503 jiffies, g=54677, q=156 ncpus=2)
task:syz.6.1344 state:R running task stack:26496 pid:10207 ppid:7812 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5244 [inline]
__schedule+0x10e9/0x40d0 kernel/sched/core.c:6561
preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6873
irqentry_exit+0x63/0x70 kernel/entry/common.c:439
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:lock_acquire+0x20f/0x490 kernel/locking/lockdep.c:5666
Code: 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 0f 85 f5 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:ffffc9000513fc80 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 9e7d513cc926b500
RDX: 0000000000000000 RSI: ffffffff8a8c15e0 RDI: ffffffff8adf1c20
RBP: ffffc9000513fd88 R08: dffffc0000000000 R09: fffffbfff215c449
R10: fffffbfff215c449 R11: 1ffffffff215c448 R12: 0000000000000000
R13: 1ffff92000a27f9c R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
rcu_read_lock include/linux/rcupdate.h:791 [inline]
mntput_no_expire+0xd3/0x850 fs/namespace.c:1208
__do_sys_chdir fs/open.c:525 [inline]
__se_sys_chdir+0x1bf/0x280 fs/open.c:508
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb2cad8d677
RSP: 002b:00007fb2cbb0fe68 EFLAGS: 00000206 ORIG_RAX: 0000000000000050
RAX: ffffffffffffffda RBX: 00007fb2cbb0fef0 RCX: 00007fb2cad8d677
RDX: 0000000000000003 RSI: 0000200000000140 RDI: 0000200000000140
RBP: 0000200000000440 R08: 0000000000000000 R09: 0000000000200000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000200000000140
R13: 00007fb2cbb0feb0 R14: 0000000000000570 R15: 0000200000000200
</TASK>
rcu: rcu_preempt kthread starved for 10525 jiffies! g54677 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
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:27552 pid:16 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5244 [inline]
__schedule+0x10e9/0x40d0 kernel/sched/core.c:6561
schedule+0xb9/0x180 kernel/sched/core.c:6637
schedule_timeout+0x15c/0x280 kernel/time/timer.c:1965
rcu_gp_fqs_loop+0x2f2/0x1310 kernel/rcu/tree.c:1706
rcu_gp_kthread+0x95/0x380 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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 10205 Comm: syz.4.1343 Not tainted 6.1.145-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:unwind_next_frame+0x6e2/0x20b0 arch/x86/kernel/unwind_orc.c:471
Code: 80 e1 07 38 c1 0f 8c 75 02 00 00 be 02 00 00 00 49 89 d6 4c 89 ff e8 bd f8 99 00 e9 3b 18 00 00 48 8b 44 24 50 42 80 3c 28 00 <4c> 8b 74 24 58 74 08 4c 89 f7 e8 df f7 99 00 49 8b 16 4d 8d 7c 24
RSP: 0018:ffffc9000515f5f0 EFLAGS: 00000046
RAX: 1ffff92000a2bee0 RBX: ffffc9000515f6c8 RCX: ffffffff8e2f33f4
RDX: ffffffff8e9f0a82 RSI: ffffffff8e2f33f0 RDI: 0000000000000001
RBP: ffffffff8e9f0a86 R08: 0000000000000009 R09: 0000000000000005
R10: fffff52000a2bee5 R11: 1ffff92000a2bee3 R12: ffffffff8e9f0a82
R13: dffffc0000000000 R14: ffffffff8e2f33f0 R15: 0000000000000005
FS: 00007f7be84906c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000077c40000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x98/0xe0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
kasan_save_free_info+0x2d/0x50 mm/kasan/generic.c:516
____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:236
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1724 [inline]
slab_free_freelist_hook+0x131/0x1a0 mm/slub.c:1750
slab_free mm/slub.c:3661 [inline]
kmem_cache_free+0xf7/0x290 mm/slub.c:3683
__sigqueue_free kernel/signal.c:459 [inline]
collect_signal kernel/signal.c:602 [inline]
__dequeue_signal+0x4e9/0x610 kernel/signal.c:624
dequeue_signal+0xe5/0x4b0 kernel/signal.c:647
get_signal+0x547/0x1350 kernel/signal.c:2751
arch_do_signal_or_restart+0xb0/0x1230 arch/x86/kernel/signal.c:871
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f7be758e929
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7be84900e8 EFLAGS: 00000246
RAX: fffffffffffffffc RBX: 00007f7be77b5fa8 RCX: 00007f7be758e929
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f7be77b5fa8
RBP: 00007f7be77b5fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7be77b5fac
R13: 0000000000000000 R14: 00007fffc20b1270 R15: 00007fffc20b1358
</TASK>
vkms_vblank_simulate: vblank timer overrun


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0a805b6ea8cd Linux 6.6.116
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1081f932580000
kernel config: https://syzkaller.appspot.com/x/.config?x=12606d4b8832c7e4
dashboard link: https://syzkaller.appspot.com/bug?extid=54aab2326e7ee4937bc5
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/13874446b4b2/disk-0a805b6e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/69a5e59e1ade/vmlinux-0a805b6e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/322c0711f976/bzImage-0a805b6e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:

Reported-by: syzbot+54aab2...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:

rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P11809/1:b..l
rcu: (detected by 0, t=10502 jiffies, g=48225, q=61 ncpus=2)
task:syz-executor state:R running task stack:28744 pid:11809 ppid:6409 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5380 [inline]
__schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
preempt_schedule_irq+0xb5/0x140 kernel/sched/core.c:7009
irqentry_exit+0x67/0x70 kernel/entry/common.c:438
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:__seqprop_spinlock_sequence include/linux/seqlock.h:275 [inline]
RIP: 0010:path_init+0x268/0x1200 fs/namei.c:2377
Code: 83 e6 01 31 ff e8 c8 ca 95 ff 89 e8 83 e0 01 48 89 5c 24 20 75 07 e8 07 c7 95 ff eb 40 48 c7 c3 40 47 a1 8c 48 c1 eb 03 f3 90 <42> 0f b6 04 3b 84 c0 75 13 8b 2d 99 7e b1 0a 40 f6 c5 01 74 19 e8
RSP: 0018:ffffc9000bd57b30 EFLAGS: 00000293
RAX: ffffffff81efc8b2 RBX: 1ffffffff19428e8 RCX: ffff88805b495a00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: 0000000000010c37 R08: dffffc0000000000 R09: 1ffffffff21b50a0
R10: dffffc0000000000 R11: fffffbfff21b50a1 R12: 1ffff1100927f444
R13: 0000000000000040 R14: ffffc9000bd57ca0 R15: dffffc0000000000
path_lookupat+0x27/0x440 fs/namei.c:2481
filename_lookup+0x1f4/0x510 fs/namei.c:2520
user_path_at_empty+0x42/0x60 fs/namei.c:2917
user_path_at include/linux/namei.h:57 [inline]
__do_sys_chdir fs/open.c:551 [inline]
__se_sys_chdir+0x95/0x290 fs/open.c:545
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7ff1f2b8e417
RSP: 002b:00007ffee6bd01f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000050
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff1f2b8e417
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 00007ffee6bd0250
RBP: 00007ffee6bd023c R08: 0000000000000000 R09: 00007ff1f391d6c0
R10: 000055557cf47500 R11: 0000000000000246 R12: 0000000000000111
R13: 00000000000927c0 R14: 00000000000b2b98 R15: 00007ffee6bd0290
</TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10501 jiffies! g48225 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: Possible timer handling issue on cpu=1 timer-softirq=45957
rcu: rcu_preempt kthread starved for 10502 jiffies! g48225 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1

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:I stack:26920 pid:17 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5380 [inline]
__schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
schedule+0xbd/0x170 kernel/sched/core.c:6773
schedule_timeout+0x160/0x280 kernel/time/timer.c:2167
rcu_gp_fqs_loop+0x302/0x1560 kernel/rcu/tree.c:1667
rcu_gp_kthread+0x99/0x380 kernel/rcu/tree.c:1866
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

</TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1

CPU: 1 PID: 11807 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:arch_atomic_try_cmpxchg arch/x86/include/asm/atomic.h:115 [inline]
RIP: 0010:raw_atomic_try_cmpxchg_acquire include/linux/atomic/atomic-arch-fallback.h:2151 [inline]
RIP: 0010:atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1296 [inline]
RIP: 0010:queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
RIP: 0010:do_raw_spin_lock+0x12e/0x2c0 kernel/locking/spinlock_debug.c:115
Code: 00 48 89 df be 04 00 00 00 e8 6e a3 74 00 48 8d 7c 24 40 be 04 00 00 00 e8 5f a3 74 00 8b 44 24 40 b9 01 00 00 00 f0 0f b1 0b <0f> 85 d9 00 00 00 65 8b 1d 51 6e 9b 7e 48 b9 00 00 00 00 00 fc ff
RSP: 0018:ffffc900001f0be0 EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffff8880b8f2b700 RCX: 0000000000000001
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc900001f0c20
RBP: ffffc900001f0c90 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff5200003e184 R12: ffff8880b8f2b710
R13: ffff8880b8f2b708 R14: 1ffff110171e56e2 R15: 1ffff110171e56e1
FS: 0000555575b45500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f0e3324f764 CR3: 000000002615a000 CR4: 00000000003506e0
Call Trace:
<IRQ>
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:120 [inline]
_raw_spin_lock_irq+0xaf/0xe0 kernel/locking/spinlock.c:170
__run_hrtimer kernel/time/hrtimer.c:1754 [inline]
__hrtimer_run_queues+0x5e3/0xc40 kernel/time/hrtimer.c:1814
hrtimer_interrupt+0x3c9/0x9c0 kernel/time/hrtimer.c:1876
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1077 [inline]
__sysvec_apic_timer_interrupt+0xfb/0x3b0 arch/x86/kernel/apic/apic.c:1094
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
sysvec_apic_timer_interrupt+0x9f/0xc0 arch/x86/kernel/apic/apic.c:1088
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:mnt_get_count+0xf8/0x160 fs/namespace.c:197
Code: 30 3a 7d 8c 4c 89 e0 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 e7 e8 a8 fa e8 ff 4d 03 3c 24 4c 89 f8 48 c1 e8 03 42 0f b6 04 28 <84> c0 75 1a 41 03 2f 41 ff c6 41 83 e6 0f 41 83 fe 07 77 3e e8 2f
RSP: 0018:ffffc9000c2d7d10 EFLAGS: 00000a02
RAX: 0000000000000000 RBX: ffff88802ddb1250 RCX: ffff88802dcd0000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: dffffc0000000000 R09: 1ffffffff21b50a2
R10: dffffc0000000000 R11: fffffbfff21b50a3 R12: ffffffff8c7d3a30
R13: dffffc0000000000 R14: 0000000000000000 R15: ffffe8ffffc3d150
mntput_no_expire+0x2b5/0x860 fs/namespace.c:1307
path_put fs/namei.c:563 [inline]
done_path_create fs/namei.c:3943 [inline]
do_symlinkat+0x210/0x3f0 fs/namei.c:4509
__do_sys_symlinkat fs/namei.c:4523 [inline]
__se_sys_symlinkat fs/namei.c:4520 [inline]
__x64_sys_symlinkat+0x99/0xb0 fs/namei.c:4520
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f0e3318ec47
Code: 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 0a 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffddc3e8208 EFLAGS: 00000202 ORIG_RAX: 000000000000010a
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0e3318ec47
RDX: 00007f0e332138ce RSI: 00000000ffffff9c RDI: 00007ffddc3e82a0
RBP: 00007ffddc3e824c R08: 0000000000000017 R09: 00007ffddc3e7f57
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000176
R13: 0000000000000056 R14: 00000000000b20df R15: 00007ffddc3e82a0
</TASK>