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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 779f9571ac3e Linux 6.1.164
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12aa15c6580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0605c5af04d7603
dashboard link: https://syzkaller.appspot.com/bug?extid=9b0e82fdbb16d97e2323
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1573c202580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14fc4794580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d8bc7a0c33a8/disk-779f9571.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/870b0bf266c7/vmlinux-779f9571.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ce1e3301c41d/bzImage-779f9571.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9b0e82...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2639 jiffies s: 3561 root: 0x1/.
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 3637 Comm: udevd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:check_kcov_mode kernel/kcov.c:182 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x2a/0x60 kernel/kcov.c:216
Code: 48 8b 04 24 65 48 8b 0d 14 fa 7f 7e 65 8b 15 15 fa 7f 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 35 83 b9 1c 16 00 00 00 <74> 2c 8b 91 f8 15 00 00 83 fa 02 75 21 48 8b 91 00 16 00 00 48 8b
RSP: 0018:ffffc900000074e0 EFLAGS: 00000046
RAX: ffffffff818ecbc8 RBX: 0000000000000101 RCX: ffff88807bd33b80
RDX: 0000000000000100 RSI: 0000000000000101 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffc90000007447 R09: 1ffff92000000e88
R10: dffffc0000000000 R11: fffff52000000e89 R12: 0000000000000000
R13: dffffc0000000001 R14: 0000000000000000 R15: 0000000000000000
FS: 00007fdb55ea4880(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f79f0d456b8 CR3: 000000002f178000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
irq_work_queue_on+0x198/0x260 kernel/irq_work.c:168
rcu_read_unlock_special+0x3c9/0x510 kernel/rcu/tree_plugin.h:678
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
rcu_read_unlock include/linux/rcupdate.h:823 [inline]
trace_call_bpf+0x5bb/0x6b0 kernel/trace/bpf_trace.c:137
perf_trace_run_bpf_submit+0x79/0x1c0 kernel/events/core.c:9997
perf_trace_preemptirq_template+0x268/0x320 include/trace/events/preemptirq.h:14
trace_irq_enable_rcuidle+0xd3/0x140 include/trace/events/preemptirq.h:40
trace_hardirqs_on+0x24/0x40 kernel/trace/trace_preemptirq.c:44
asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
RIP: 0010:rcu_read_unlock_special+0x7f/0x510 kernel/rcu/tree_plugin.h:685
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 92 31 95 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc90000007980 EFLAGS: 00000206
RAX: 3902b81ee1219000 RBX: 1ffff92000000f38 RCX: 3902b81ee1219000
RDX: dffffc0000000000 RSI: ffffffff8a8c1220 RDI: ffffffff8adf0de0
RBP: ffffc90000007a80 R08: ffffffff90af533f R09: 1ffffffff215ea67
R10: dffffc0000000000 R11: fffffbfff215ea68 R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8e3b900 R15: 0000000000000001
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
rcu_read_unlock include/linux/rcupdate.h:823 [inline]
hsr_announce+0x2ca/0x340 net/hsr/hsr_device.c:407
call_timer_fn+0x1ac/0x670 kernel/time/timer.c:1701
expire_timers kernel/time/timer.c:1752 [inline]
__run_timers+0x53e/0x800 kernel/time/timer.c:2023
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:2036
handle_softirqs+0x2a1/0x930 kernel/softirq.c:596
__do_softirq kernel/softirq.c:630 [inline]
invoke_softirq kernel/softirq.c:470 [inline]
__irq_exit_rcu+0x13b/0x230 kernel/softirq.c:679
irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 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:ffffc90002f87ae0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 3902b81ee1219000
RDX: 0000000000000000 RSI: ffffffff8a8c23a0 RDI: ffffffff8adf0de0
RBP: ffffc90002f87bf0 R08: dffffc0000000000 R09: 1ffffffff215ea4a
R10: dffffc0000000000 R11: fffffbfff215ea4b R12: 0000000000000000
R13: 1ffff920005f0f68 R14: 0000000000000246 R15: dffffc0000000000
fs_reclaim_acquire+0x94/0x100 mm/page_alloc.c:4765
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]
__kmem_cache_alloc_node+0x4f/0x260 mm/slub.c:3398
kmalloc_trace+0x26/0xe0 mm/slab_common.c:1026
kmalloc include/linux/slab.h:563 [inline]
kzalloc include/linux/slab.h:699 [inline]
kernfs_iop_get_link+0x63/0x5a0 fs/kernfs/symlink.c:135
vfs_readlink+0x179/0x3e0 fs/namei.c:5131
do_readlinkat+0x251/0x490 fs/stat.c:480
__do_sys_readlink fs/stat.c:501 [inline]
__se_sys_readlink fs/stat.c:498 [inline]
__x64_sys_readlink+0x7b/0x90 fs/stat.c:498
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: 0033:0x7fdb557153a7
Code: 00 00 90 48 83 ec 10 48 63 ff 45 31 c9 45 31 c0 6a 00 31 c9 e8 8a 20 f9 ff 48 83 c4 18 c3 0f 1f 44 00 00 b8 59 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 8b 15 21 ba 0d 00 f7 d8 64 89 02 48
RSP: 002b:00007ffee49841d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffee49846b0 RCX: 00007fdb557153a7
RDX: 0000000000000400 RSI: 00007ffee49841e0 RDI: 00007ffee49846b0
RBP: 00007ffee49841e0 R08: 0000000000000075 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000400
R13: 00005596492d8100 R14: 0000000000000000 R15: 00007ffee4985fb0
</TASK>


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