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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0182cb5b74ee Linux 6.1.162
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14816b22580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0605c5af04d7603
dashboard link: https://syzkaller.appspot.com/bug?extid=b495dbcfcc675f413151
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/91a9c745b7a1/disk-0182cb5b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a26ca15eb2ec/vmlinux-0182cb5b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/767cda5049bb/bzImage-0182cb5b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b495db...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P4476/1:b..l
(detected by 1, t=10502 jiffies, g=9157, q=592 ncpus=2)
task:syz.0.21 state:R running task stack:26480 pid:4476 ppid:4268 flags:0x00004004
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5245 [inline]
__schedule+0x11d1/0x40e0 kernel/sched/core.c:6562
preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6874
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:rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
RIP: 0010:rcu_read_lock include/linux/rcupdate.h:791 [inline]
RIP: 0010:page_ext_get+0x3a/0x2a0 mm/page_ext.c:157
Code: a4 ff e8 09 a6 8f ff 48 8d 1d 00 00 00 00 48 c7 c7 20 d6 b2 8c 31 f6 31 d2 b9 02 00 00 00 45 31 c0 45 31 c9 53 e8 56 a8 86 ff <48> 83 c4 08 e8 1d 05 4f 08 89 c5 31 ff 89 c6 e8 c2 e0 a4 ff 85 ed
RSP: 0018:ffffc90004c1f680 EFLAGS: 00000246
RAX: f9fe60f2e4cf8300 RBX: ffffffff81dd961e RCX: f9fe60f2e4cf8300
RDX: 0000000000000000 RSI: ffffffff8a8c23a0 RDI: ffffffff8adf0d20
RBP: 0000000000000000 R08: dffffc0000000000 R09: 1ffffffff215e848
R10: dffffc0000000000 R11: fffffbfff215e849 R12: 0000000000000000
R13: 0000000000000000 R14: ffffea0000b974c0 R15: ffffea0000b974c0
__reset_page_owner+0x31/0x1a0 mm/page_owner.c:144
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1486 [inline]
free_pcp_prepare mm/page_alloc.c:1536 [inline]
free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3413
free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3508
free_slab mm/slub.c:2036 [inline]
discard_slab mm/slub.c:2042 [inline]
__unfreeze_partials+0x1a5/0x200 mm/slub.c:2591
put_cpu_partial+0x17c/0x250 mm/slub.c:2667
qlink_free mm/kasan/quarantine.c:168 [inline]
qlist_free_all+0x76/0xe0 mm/kasan/quarantine.c:187
kasan_quarantine_reduce+0x144/0x160 mm/kasan/quarantine.c:294
__kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:306
kasan_slab_alloc include/linux/kasan.h:201 [inline]
slab_post_alloc_hook+0x4b/0x480 mm/slab.h:737
slab_alloc_node mm/slub.c:3359 [inline]
__kmem_cache_alloc_node+0x140/0x260 mm/slub.c:3398
__do_kmalloc_node mm/slab_common.c:935 [inline]
__kmalloc+0xa0/0x240 mm/slab_common.c:949
kmalloc include/linux/slab.h:568 [inline]
tomoyo_realpath_from_path+0xdf/0x5d0 security/tomoyo/realpath.c:251
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_number_perm+0x22f/0x650 security/tomoyo/file.c:723
tomoyo_path_mknod+0x147/0x190 security/tomoyo/tomoyo.c:239
security_path_mknod+0xec/0x140 security/security.c:1166
do_mknodat+0x245/0x4d0 fs/namei.c:4035
__do_sys_mknod fs/namei.c:4076 [inline]
__se_sys_mknod fs/namei.c:4074 [inline]
__x64_sys_mknod+0x8a/0xa0 fs/namei.c:4074
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: 0033:0x7f7b5dd9aeb9
RSP: 002b:00007f7b5eb90028 EFLAGS: 00000246 ORIG_RAX: 0000000000000085
RAX: ffffffffffffffda RBX: 00007f7b5e015fa0 RCX: 00007f7b5dd9aeb9
RDX: 0000000000008001 RSI: 0000000008001420 RDI: 0000200000000040
RBP: 00007f7b5de08c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7b5e016038 R14: 00007f7b5e015fa0 R15: 00007fff8d2feb88
</TASK>
rcu: rcu_preempt kthread starved for 9340 jiffies! g9157 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:26864 pid:16 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5245 [inline]
__schedule+0x11d1/0x40e0 kernel/sched/core.c:6562
schedule+0xb9/0x180 kernel/sched/core.c:6638
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2168
rcu_gp_fqs_loop+0x303/0x1340 kernel/rcu/tree.c:1706
rcu_gp_kthread+0x99/0x3b0 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:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:default_idle+0xb/0x10 arch/x86/kernel/process.c:742
Code: 48 89 df e8 97 d1 9c f7 e9 44 ff ff ff e8 3d 07 f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 66 90 0f 00 2d 77 1c 50 00 fb f4 <c3> 0f 1f 40 00 41 57 41 56 53 49 be 00 00 00 00 00 fc ff df 65 48
RSP: 0018:ffffc90000177de8 EFLAGS: 000002c6
RAX: debc547fad802b00 RBX: ffffffff8a3692b7 RCX: debc547fad802b00
RDX: 0000000000000001 RSI: ffffffff8a8c1220 RDI: ffffffff8adf0d20
RBP: ffffc90000177f20 R08: ffff8880b8f3580b R09: 1ffff110171e6b01
R10: dffffc0000000000 R11: ffffed10171e6b02 R12: 1ffff9200002efc8
R13: dffffc0000000000 R14: ffff888017739dc0 R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fea46dc36c8 CR3: 0000000026987000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
default_idle_call+0x84/0xc0 kernel/sched/idle.c:109
cpuidle_idle_call kernel/sched/idle.c:191 [inline]
do_idle+0x20d/0x5a0 kernel/sched/idle.c:303
cpu_startup_entry+0x3f/0x60 kernel/sched/idle.c:401
start_secondary+0xe4/0xf0 arch/x86/kernel/smpboot.c:281
secondary_startup_64_no_verify+0xcf/0xdb
</TASK>


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