[v5.15] INFO: rcu detected stall in sys_unlink (5)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 43bb85222e53 Linux 5.15.193
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12f2b4e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e1bb6d24ef2164eb
dashboard link: https://syzkaller.appspot.com/bug?extid=5854e0c59e957bb696cd
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/0bc183664ae8/disk-43bb8522.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0fc2f6618934/vmlinux-43bb8522.xz
kernel image: https://storage.googleapis.com/syzbot-assets/af70b3957f4c/bzImage-43bb8522.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5854e0...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 0-....: (1 GPs behind) idle=0ff/1/0x4000000000000002 softirq=72566/72567 fqs=5246
(detected by 1, t=10502 jiffies, g=98073, q=850)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 18551 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x60 kernel/kcov.c:202
Code: 66 2e 0f 1f 84 00 00 00 00 00 53 48 89 fb e8 17 00 00 00 48 8b 3d 00 c9 f1 0b 48 89 de 5b e9 47 9e 43 00 00 00 cc cc 00 00 cc <48> 8b 04 24 65 48 8b 0d 94 a4 8a 7e 65 8b 15 95 a4 8a 7e 81 e2 00
RSP: 0018:ffffc90000007138 EFLAGS: 00000046
RAX: ffffffff8196e2ce RBX: 1ffff11017206a4a RCX: ffff888021170000
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900000073a8 R08: dffffc0000000000 R09: fffffbfff1ad323e
R10: fffffbfff1ad323e R11: 1ffffffff1ad323d R12: ffff8880b9035250
R13: ffff8880242b3bb0 R14: 0000000000000000 R15: 0000000000000000
FS: 000055558fb5e500(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc2b296e68 CR3: 000000004f0e0000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
perf_tp_event_match kernel/events/core.c:10000 [inline]
perf_tp_event+0x269/0xb50 kernel/events/core.c:10046
perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10021
perf_trace_preemptirq_template+0x2be/0x380 include/trace/events/preemptirq.h:14
trace_irq_enable_rcuidle+0x108/0x180 include/trace/events/preemptirq.h:40
trace_hardirqs_on+0x57/0x80 kernel/trace/trace_preemptirq.c:44
asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x84/0x480 kernel/rcu/tree_plugin.h:674
Code: f1 f1 f1 00 f2 f2 f2 4a 89 04 2b 66 42 c7 44 2b 09 f3 f3 42 c6 44 2b 0b f3 65 44 8b 35 ad 13 9e 7e 41 f7 c6 00 00 f0 00 74 45 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 66 42 c7 44 2b
RSP: 0018:ffffc90000007600 EFLAGS: 00000206
RAX: 3dd7faf787fcfb00 RBX: 1ffff92000000ec4 RCX: 3dd7faf787fcfb00
RDX: dffffc0000000000 RSI: ffffffff8a0b1820 RDI: ffffffff8a59a480
RBP: ffffc900000076e0 R08: dffffc0000000000 R09: fffffbfff1ff7833
R10: fffffbfff1ff7833 R11: 1ffffffff1ff7832 R12: ffffffff8c120b00
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
rcu_read_unlock include/linux/rcupdate.h:771 [inline]
ndisc_send_skb+0xdc4/0x14a0 net/ipv6/ndisc.c:521
ndisc_send_ns+0x63c/0x840 net/ipv6/ndisc.c:655
ndisc_solicit+0x2f8/0x4e0 net/ipv6/ndisc.c:747
neigh_probe net/core/neighbour.c:1017 [inline]
neigh_timer_handler+0xaa9/0xfe0 net/core/neighbour.c:1099
call_timer_fn+0x16c/0x530 kernel/time/timer.c:1451
expire_timers kernel/time/timer.c:1496 [inline]
__run_timers+0x525/0x7c0 kernel/time/timer.c:1767
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
handle_softirqs+0x328/0x820 kernel/softirq.c:576
__do_softirq kernel/softirq.c:610 [inline]
invoke_softirq kernel/softirq.c:450 [inline]
__irq_exit_rcu+0x12f/0x220 kernel/softirq.c:659
irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:seqcount_lockdep_reader_access+0x17b/0x1c0 include/linux/seqlock.h:106
Code: 00 4d 85 e4 75 16 e8 54 cc 0f 00 eb 15 e8 4d cc 0f 00 e8 88 ef 40 08 4d 85 e4 74 ea e8 3e cc 0f 00 fb 48 c7 04 24 0e 36 e0 45 <4b> c7 04 3e 00 00 00 00 66 43 c7 44 3e 09 00 00 43 c6 44 3e 0b 00
RSP: 0018:ffffc9000337fb80 EFLAGS: 00000293
RAX: ffffffff8167fee2 RBX: 0000000000000000 RCX: ffff888021170000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000337fc28 R08: dffffc0000000000 R09: fffffbfff1ff782c
R10: fffffbfff1ff782c R11: 1ffffffff1ff782b R12: 0000000000000200
R13: dffffc0000000000 R14: 1ffff9200066ff70 R15: dffffc0000000000
ktime_get_coarse_real_ts64+0x36/0x120 kernel/time/timekeeping.c:2244
current_time+0x86/0x2b0 fs/inode.c:2391
shmem_unlink+0x181/0x260 mm/shmem.c:2955
vfs_unlink+0x385/0x600 fs/namei.c:4280
do_unlinkat+0x382/0x6f0 fs/namei.c:4348
__do_sys_unlink fs/namei.c:4396 [inline]
__se_sys_unlink fs/namei.c:4394 [inline]
__x64_sys_unlink+0x45/0x50 fs/namei.c:4394
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: 0033:0x7fe37c81a477
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 57 00 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:00007ffc2b297618 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe37c81a477
RDX: 00007ffc2b297640 RSI: 00007ffc2b2976d0 RDI: 00007ffc2b2976d0
RBP: 00007ffc2b2976d0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000100 R11: 0000000000000206 R12: 00007ffc2b298760
R13: 00007fe37c89dd7d R14: 00000000000a1fc7 R15: 00007ffc2b2987a0
</TASK>


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