[syzbot] [tomoyo?] [mm?] INFO: rcu detected stall in sys_newfstat (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 12b95d29eb97 Add linux-next specific files for 20251217
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16bbd31a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9b53f0e28d100777
dashboard link: https://syzkaller.appspot.com/bug?extid=5fb7dcd004f42cb418d7
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11355d92580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0264b4454f47/disk-12b95d29.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/72a383625b53/vmlinux-12b95d29.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6499b25d444f/bzImage-12b95d29.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5fb7dc...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P5966/1:b..l
rcu: (detected by 0, t=10502 jiffies, g=13749, q=681 ncpus=2)
task:udevd state:R running task stack:24376 pid:5966 tgid:5966 ppid:5200 task_flags:0x400140 flags:0x00080000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5258 [inline]
__schedule+0x150e/0x5070 kernel/sched/core.c:6866
preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7193
irqentry_exit+0x5d8/0x660 kernel/entry/common.c:216
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:lock_acquire+0x16c/0x340 kernel/locking/lockdep.c:5872
Code: 00 00 00 00 9c 8f 44 24 30 f7 44 24 30 00 02 00 00 0f 85 cd 00 00 00 f7 44 24 08 00 02 00 00 74 01 fb 65 48 8b 05 74 3f 25 11 <48> 3b 44 24 58 0f 85 e5 00 00 00 48 83 c4 60 5b 41 5c 41 5d 41 5e
RSP: 0018:ffffc900035174d8 EFLAGS: 00000206
RAX: 550ae36b7d32a800 RBX: 0000000000000000 RCX: 550ae36b7d32a800
RDX: 0000000002aa642d RSI: ffffffff8dc9133e RDI: ffffffff8be243e0
RBP: ffffffff81746f85 R08: ffffffff81746f85 R09: ffffffff8e33f8a0
R10: ffffc90003517698 R11: ffffffff81addf20 R12: 0000000000000002
R13: ffffffff8e33f8a0 R14: 0000000000000000 R15: 0000000000000246
rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
rcu_read_lock include/linux/rcupdate.h:867 [inline]
class_rcu_constructor include/linux/rcupdate.h:1195 [inline]
unwind_next_frame+0xc2/0x23d0 arch/x86/kernel/unwind_orc.c:495
arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2540 [inline]
slab_free mm/slub.c:6674 [inline]
kfree+0x1c0/0x660 mm/slub.c:6882
tomoyo_realpath_from_path+0x598/0x5d0 security/tomoyo/realpath.c:286
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_perm+0x213/0x4b0 security/tomoyo/file.c:822
security_inode_getattr+0x12f/0x330 security/security.c:1869
vfs_getattr fs/stat.c:259 [inline]
vfs_fstat fs/stat.c:281 [inline]
__do_sys_newfstat fs/stat.c:555 [inline]
__se_sys_newfstat fs/stat.c:550 [inline]
__x64_sys_newfstat+0xfc/0x200 fs/stat.c:550
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fcf92911ad7
RSP: 002b:00007ffe4ab44048 EFLAGS: 00000246 ORIG_RAX: 0000000000000005
RAX: ffffffffffffffda RBX: 00005558e4439050 RCX: 00007fcf92911ad7
RDX: 0000000000000000 RSI: 00007ffe4ab44090 RDI: 0000000000000009
RBP: 0000000000000001 R08: 0000000000000620 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00005558ba62e95f
R13: 00005558ba63f660 R14: 0000000000000000 R15: 0000000000000009
</TASK>
rcu: rcu_preempt kthread starved for 10446 jiffies! g13749 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:27728 pid:16 tgid:16 ppid:2 task_flags:0x208040 flags:0x00080000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5258 [inline]
__schedule+0x150e/0x5070 kernel/sched/core.c:6866
__schedule_loop kernel/sched/core.c:6948 [inline]
schedule+0x165/0x360 kernel/sched/core.c:6963
schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99
rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083
rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:82
Code: cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 33 be 21 00 f3 0f 1e fa fb f4 <e9> 48 ee 02 00 cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffffff8e007d80 EFLAGS: 000002c6
RAX: da29ab50f81b1900 RBX: ffffffff8197c88a RCX: da29ab50f81b1900
RDX: 0000000000000001 RSI: ffffffff8daa76bd RDI: ffffffff8be243e0
RBP: ffffffff8e007ea8 R08: ffff8880b86336db R09: 1ffff110170c66db
R10: dffffc0000000000 R11: ffffed10170c66dc R12: ffffffff8fc3b070
R13: 1ffffffff1c129b8 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881259e1000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31163fff CR3: 0000000077280000 CR4: 00000000003526f0
Call Trace:
<TASK>
arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
default_idle+0x13/0x20 arch/x86/kernel/process.c:767
default_idle_call+0x73/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:191 [inline]
do_idle+0x1ea/0x520 kernel/sched/idle.c:332
cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:430
rest_init+0x2de/0x300 init/main.c:757
start_kernel+0x3a7/0x400 init/main.c:1206
x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:291
common_startup_64+0x13e/0x147
</TASK>


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