[v5.15] INFO: rcu detected stall in sys_readlink (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f45bea23c39c Linux 5.15.162
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12d6346e980000
kernel config: https://syzkaller.appspot.com/x/.config?x=e4bf7e31dc0c0a74
dashboard link: https://syzkaller.appspot.com/bug?extid=4266c312676f3f5f97e1
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4d8c24af3786/disk-f45bea23.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e3446b6ec2ee/vmlinux-f45bea23.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0fb8209336b0/bzImage-f45bea23.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4266c3...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P2962/1:b..l
(detected by 1, t=10502 jiffies, g=4593, q=70)
task:udevd state:R running task stack:25080 pid: 2962 ppid: 1 flags:0x00004002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5030 [inline]
__schedule+0x12c4/0x45b0 kernel/sched/core.c:6376
preempt_schedule_irq+0xf7/0x1c0 kernel/sched/core.c:6780
irqentry_exit+0x53/0x80 kernel/entry/common.c:432
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:638
RIP: 0010:lock_acquire+0x252/0x4f0 kernel/locking/lockdep.c:5627
Code: 2b 00 74 08 4c 89 f7 e8 ac 7e 67 00 f6 44 24 61 02 0f 85 84 01 00 00 41 f7 c7 00 02 00 00 74 01 fb 48 c7 44 24 40 0e 36 e0 45 <4b> c7 44 25 00 00 00 00 00 43 c7 44 25 09 00 00 00 00 43 c7 44 25
RSP: 0018:ffffc90002dc7640 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 1ffff920005b8ed4 RCX: 1ffff920005b8e74
RDX: dffffc0000000000 RSI: ffffffff8a8b3ca0 RDI: ffffffff8ad8f680
RBP: ffffc90002dc7788 R08: dffffc0000000000 R09: fffffbfff1f7f219
R10: 0000000000000000 R11: dffffc0000000001 R12: 1ffff920005b8ed0
R13: dffffc0000000000 R14: ffffc90002dc76a0 R15: 0000000000000246
rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:312
rcu_read_lock include/linux/rcupdate.h:739 [inline]
dput+0x35/0x1a0 fs/dcache.c:875
step_into+0x352/0xe90 fs/namei.c:1815
walk_component+0x359/0x610 fs/namei.c:1982
link_path_walk+0x642/0xd90
path_lookupat+0xa9/0x450 fs/namei.c:2454
filename_lookup+0x230/0x5c0 fs/namei.c:2484
user_path_at_empty+0x40/0x180 fs/namei.c:2883
do_readlinkat+0x114/0x3a0 fs/stat.c:442
__do_sys_readlink fs/stat.c:475 [inline]
__se_sys_readlink fs/stat.c:472 [inline]
__x64_sys_readlink+0x7b/0x90 fs/stat.c:472
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fb6fb64ad47
RSP: 002b:00007ffd150a4338 EFLAGS: 00000246 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffd150a4348 RCX: 00007fb6fb64ad47
RDX: 0000000000000400 RSI: 00007ffd150a4348 RDI: 00007ffd150a4828
RBP: 0000000000000400 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000010f R11: 0000000000000246 R12: 00007ffd150a4828
R13: 00007ffd150a4798 R14: 000055d13bc19910 R15: 0000000000000000
</TASK>
rcu: rcu_preempt kthread starved for 10468 jiffies! g4593 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:27352 pid: 15 ppid: 2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5030 [inline]
__schedule+0x12c4/0x45b0 kernel/sched/core.c:6376
schedule+0x11b/0x1f0 kernel/sched/core.c:6459
schedule_timeout+0x1b9/0x300 kernel/time/timer.c:1914
rcu_gp_fqs_loop+0x2bf/0x1080 kernel/rcu/tree.c:1972
rcu_gp_kthread+0xa4/0x360 kernel/rcu/tree.c:2145
kthread+0x3f6/0x4f0 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:300
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 0 skipped: idling at acpi_safe_halt drivers/acpi/processor_idle.c:109 [inline]
NMI backtrace for cpu 0 skipped: idling at acpi_idle_do_entry+0x10f/0x340 drivers/acpi/processor_idle.c:570


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