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

[syzbot]

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=17444612580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7eb38bd5021fec61
dashboard link: https://syzkaller.appspot.com/bug?extid=62375c93699b93e0d34d
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+62375c...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P4496/1:b..l
(detected by 0, t=10502 jiffies, g=10201, q=409 ncpus=2)
task:modprobe state:R running task stack:24352 pid:4496 ppid:4432 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:__sanitizer_cov_trace_const_cmp8+0x7a/0x80 kernel/kcov.c:322
Code: c1 e1 05 4c 8d 51 28 4d 39 ca 77 1e 49 ff c0 4c 89 02 48 c7 44 0a 08 07 00 00 00 48 89 7c 0a 10 48 89 74 0a 18 48 89 44 0a 20 <c3> 0f 1f 44 00 00 48 8b 4e 08 48 83 c1 f8 48 c1 c1 3d 48 83 f9 07
RSP: 0018:ffffc9000502fa88 EFLAGS: 00000293
RAX: ffffffff81e5217f RBX: 0000000000000000 RCX: ffff888029b99dc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000006 R08: dffffc0000000000 R09: ffffed1004ad1272
R10: ffffed1004ad1272 R11: 1ffff11004ad1271 R12: ffff888057edc42d
R13: ffff888025689388 R14: 00006769666e6f63 R15: 0000ffffffffffff
dentry_string_cmp fs/dcache.c:239 [inline]
dentry_cmp fs/dcache.c:278 [inline]
__d_lookup_rcu+0x31f/0x4c0 fs/dcache.c:2413
lookup_fast+0xca/0x4d0 fs/namei.c:1633
walk_component+0x55/0x3f0 fs/namei.c:2002
lookup_last fs/namei.c:2463 [inline]
path_lookupat+0x169/0x440 fs/namei.c:2487
filename_lookup+0x1f0/0x500 fs/namei.c:2516
user_path_at_empty+0x3e/0x60 fs/namei.c:2913
user_path_at include/linux/namei.h:57 [inline]
do_faccessat+0x3eb/0xa40 fs/open.c:446
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: 0033:0x7f6af369d2c7
RSP: 002b:00007ffc15b90c08 EFLAGS: 00000246 ORIG_RAX: 0000000000000015
RAX: ffffffffffffffda RBX: 00007f6af357f4d0 RCX: 00007f6af369d2c7
RDX: 000055bcc2477010 RSI: 0000000000000000 RDI: 00007f6af3578326
RBP: 0000000000000004 R08: 00000000000001e0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc15b90cf8
R13: 00007ffc15b90d20 R14: 00007f6af357f4d0 R15: 0000000000000000
</TASK>
rcu: rcu_preempt kthread starved for 9786 jiffies! g10201 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: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 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:741
sched: RT throttling activated


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