[v6.1] INFO: rcu detected stall in sys_readlink (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 58485ff1a74f Linux 6.1.141
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10cbf5d4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c186557a18643a0b
dashboard link: https://syzkaller.appspot.com/bug?extid=c7e9d088857fe2e3be05
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/467cd5b7e60b/disk-58485ff1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/df87a7313b47/vmlinux-58485ff1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/597ae3da22ce/bzImage-58485ff1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c7e9d0...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P3623/1:b..l
(detected by 0, t=10502 jiffies, g=123757, q=77 ncpus=2)
task:udevd state:R running task stack:23040 pid:3623 ppid:1 flags:0x00004002
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:ffffc90003257820 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ed451cf5aa6b8d00
RDX: 0000000000000000 RSI: ffffffff8a6c1160 RDI: ffffffff8abf1360
RBP: ffffc90003257930 R08: dffffc0000000000 R09: fffffbfff2117049
R10: fffffbfff2117049 R11: 1ffffffff2117048 R12: 0000000000000001
R13: 1ffff9200064af10 R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
rcu_read_lock include/linux/rcupdate.h:791 [inline]
__d_lookup+0xa8/0x7c0 fs/dcache.c:2488
lookup_fast+0x7c/0x4d0 fs/namei.c:1648
walk_component fs/namei.c:1994 [inline]
link_path_walk+0x5f2/0xe50 fs/namei.c:2325
path_lookupat+0x9d/0x440 fs/namei.c:2478
filename_lookup+0x1f0/0x500 fs/namei.c:2508
user_path_at_empty+0x3e/0x60 fs/namei.c:2905
do_readlinkat+0xd4/0x480 fs/stat.c:468
__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:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f138bb153a7
RSP: 002b:00007ffcd38016d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffcd3801bb0 RCX: 00007f138bb153a7
RDX: 0000000000000400 RSI: 00007ffcd38016e0 RDI: 00007ffcd3801bb0
RBP: 00007ffcd38016e0 R08: 0000557d474fc104 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000400
R13: 00000000000000fe R14: 0000557d378aebe0 R15: 00007ffcd38026b0
</TASK>
rcu: rcu_preempt kthread starved for 10340 jiffies! g123757 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:27712 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 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 1 skipped: idling at default_idle+0xb/0x10 arch/x86/kernel/process.c:735


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[syzbot]

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