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

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Nov 7, 2025, 3:46:31 AM (14 days ago) Nov 7
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Hello,

syzbot found the following issue on:

HEAD commit: f6e38ae624cf Linux 6.1.158
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=158e10b4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7eb38bd5021fec61
dashboard link: https://syzkaller.appspot.com/bug?extid=abfccaaae7ff1a733faa
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/2b7003e2661d/disk-f6e38ae6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0696cea8d016/vmlinux-f6e38ae6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6b7a89e636d7/bzImage-f6e38ae6.xz

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

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P3637/1:b..l
(detected by 1, t=10503 jiffies, g=12513, q=32 ncpus=2)
task:udevd state:R running task stack:23584 pid:3637 ppid:1 flags:0x00004002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5244 [inline]
__schedule+0x10ec/0x40b0 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:ffffc90003317b60 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 8c56f0503cf42b00
RDX: 0000000000000000 RSI: ffffffff8a8c1700 RDI: ffffffff8adef760
RBP: ffffc90003317c68 R08: dffffc0000000000 R09: fffffbfff215c449
R10: fffffbfff215c449 R11: 1ffffffff215c448 R12: 0000000000000000
R13: 1ffff92000662f78 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:1217
__fput+0x611/0x920 fs/file_table.c:331
task_work_run+0x1ca/0x250 kernel/task_work.c:203
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
exit_to_user_mode_prepare+0xee/0x180 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: 0033:0x7faa57aa7407
RSP: 002b:00007ffd5e968d80 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 00007faa58197880 RCX: 00007faa57aa7407
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000000000c
RBP: 00007faa581976e8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
R13: 00000000ffffffff R14: ffffffffffffffff R15: 00007ffd5e9690b0
</TASK>
rcu: rcu_preempt kthread starved for 10533 jiffies! g12513 f0x0 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:27840 pid:16 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5244 [inline]
__schedule+0x10ec/0x40b0 kernel/sched/core.c:6561
schedule+0xb9/0x180 kernel/sched/core.c:6637
schedule_timeout+0x15c/0x280 kernel/time/timer.c:2167
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 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 5243 Comm: syz.3.309 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:arch_static_branch arch/x86/include/asm/jump_label.h:27 [inline]
RIP: 0010:static_key_false include/linux/jump_label.h:207 [inline]
RIP: 0010:native_write_msr arch/x86/include/asm/msr.h:147 [inline]
RIP: 0010:wrmsrl arch/x86/include/asm/msr.h:262 [inline]
RIP: 0010:native_x2apic_icr_write arch/x86/include/asm/apic.h:239 [inline]
RIP: 0010:__x2apic_send_IPI_dest arch/x86/kernel/apic/x2apic_phys.c:126 [inline]
RIP: 0010:x2apic_send_IPI+0x70/0xd0 arch/x86/kernel/apic/x2apic_phys.c:48
Code: f0 48 c1 e8 03 42 0f b6 04 20 84 c0 75 3b 41 0f b7 16 0f ae f0 0f ae e8 83 fb 02 b8 00 04 00 00 0f 45 c3 b9 30 08 00 00 0f 30 <66> 90 5b 41 5c 41 5e 41 5f 5d c3 89 fe 89 fd 48 c7 c7 80 6d 99 8c
RSP: 0018:ffffc90000007da8 EFLAGS: 00000002
RAX: 00000000000000fd RBX: 00000000000000fd RCX: 0000000000000830
RDX: 0000000000000001 RSI: 00000000000000fd RDI: 0000000000000001
RBP: 0000000000000001 R08: dffffc0000000000 R09: fffffbfff1c3ed56
R10: fffffbfff1c3ed56 R11: 1ffffffff1c3ed55 R12: dffffc0000000000
R13: ffff88802689bb80 R14: ffff8880b8f219b0 R15: ffffffff8c5e4988
FS: 00007f838baa56c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff90cc660aa CR3: 000000007b940000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
smp_send_reschedule arch/x86/include/asm/smp.h:104 [inline]
kick_process+0xca/0x140 kernel/sched/core.c:3411
__send_signal_locked+0xb0a/0xde0 kernel/signal.c:1195
do_send_sig_info kernel/signal.c:1301 [inline]
group_send_sig_info+0x1f6/0x250 kernel/signal.c:1449
do_bpf_send_signal+0x7b/0x150 kernel/trace/bpf_trace.c:840
irq_work_single+0xd1/0x230 kernel/irq_work.c:211
irq_work_run_list kernel/irq_work.c:242 [inline]
irq_work_run+0x152/0x2e0 kernel/irq_work.c:251
__sysvec_irq_work+0xba/0x350 arch/x86/kernel/irq_work.c:22
instr_sysvec_irq_work arch/x86/kernel/irq_work.c:17 [inline]
sysvec_irq_work+0x98/0xc0 arch/x86/kernel/irq_work.c:17
</IRQ>
<TASK>
asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
RIP: 0010:arch_static_branch arch/x86/include/asm/jump_label.h:27 [inline]
RIP: 0010:static_key_false include/linux/jump_label.h:207 [inline]
RIP: 0010:native_write_msr arch/x86/include/asm/msr.h:147 [inline]
RIP: 0010:wrmsr arch/x86/include/asm/msr.h:254 [inline]
RIP: 0010:native_apic_msr_write+0x35/0x50 arch/x86/include/asm/apic.h:206
Code: 74 2a 83 ff 30 74 25 eb 10 81 ff d0 00 00 00 74 1b 81 ff e0 00 00 00 74 13 c1 ef 04 81 c7 00 08 00 00 89 f9 89 f0 31 d2 0f 30 <66> 90 c3 89 f6 31 d2 e9 1f ea f7 02 66 2e 0f 1f 84 00 00 00 00 00
RSP: 0018:ffffc9000767fcb0 EFLAGS: 00000246
RAX: 00000000000000f6 RBX: ffffffff8c5e4b88 RCX: 000000000000083f
RDX: 0000000000000000 RSI: 00000000000000f6 RDI: 000000000000083f
RBP: 0000000000000000 R08: dffffc0000000000 R09: fffff52000ecff85
R10: fffff52000ecff85 R11: 1ffff92000ecff84 R12: ffff8880b8e33e01
R13: dffffc0000000000 R14: dffffc0000000000 R15: 0000000000000020
arch_irq_work_raise+0x82/0xd0 arch/x86/kernel/irq_work.c:31
irq_work_queue+0x95/0x140 kernel/irq_work.c:114
bpf_send_signal_common+0x2b2/0x420 kernel/trace/bpf_trace.c:879
____bpf_send_signal kernel/trace/bpf_trace.c:888 [inline]
bpf_send_signal+0x15/0x20 kernel/trace/bpf_trace.c:886
bpf_prog_7ba5217f62dcd359+0x38/0x3c
bpf_dispatcher_nop_func include/linux/bpf.h:1012 [inline]
__bpf_prog_run include/linux/filter.h:603 [inline]
bpf_prog_run include/linux/filter.h:610 [inline]
__bpf_trace_run kernel/trace/bpf_trace.c:2285 [inline]
bpf_trace_run2+0x1cd/0x3b0 kernel/trace/bpf_trace.c:2324
__bpf_trace_sys_enter+0x60/0x70 include/trace/events/syscalls.h:18
trace_sys_enter+0x6b/0x80 include/trace/events/syscalls.h:18
syscall_trace_enter+0xf0/0x150 kernel/entry/common.c:81
do_syscall_64+0x24/0xa0 arch/x86/entry/common.c:77
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f838ab2b779
Code: 64 c7 00 16 00 00 00 b8 ff ff ff ff c3 0f 1f 40 00 90 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 c7 c0 0f 00 00 00 0f 05 <0f> 1f 80 00 00 00 00 48 81 ec 48 01 00 00 49 89 d0 64 48 8b 04 25
RSP: 002b:00007f838baa4b40 EFLAGS: 00000246 ORIG_RAX: 000000000000000f
RAX: ffffffffffffffda RBX: 00007f838ade6098 RCX: 00007f838ab2b779
RDX: 00007f838baa4b40 RSI: 00007f838baa4c70 RDI: 0000000000000011
RBP: 00007f838ade6090 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f838ade6128 R14: 00007ffeb2564d50 R15: 00007ffeb2564e38
</TASK>


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