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

[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=119cfcc2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7eb38bd5021fec61
dashboard link: https://syzkaller.appspot.com/bug?extid=cd4e720b12e1f66b0b11
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+cd4e72...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P4602/1:b..l
(detected by 1, t=10502 jiffies, g=8217, q=31 ncpus=2)
task:syz.3.51 state:R running task stack:26704 pid:4602 ppid:4261 flags:0x00004000
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:__rcu_read_unlock+0x2/0xd0 kernel/rcu/tree_plugin.h:419
Code: 11 ff 03 8b 03 3d 00 00 00 40 7d 02 5b c3 0f 0b eb fa 89 d9 80 e1 07 80 c1 03 38 c1 7c e3 48 89 df e8 42 28 65 00 eb d9 41 57 <41> 56 41 55 41 54 53 49 bf 00 00 00 00 00 fc ff df 65 48 8b 3d 15
RSP: 0018:ffffc900050ff498 EFLAGS: 00000202
RAX: 0000000000000001 RBX: ffffffff81d83a69 RCX: fa8c42af84fcb000
RDX: 0000000000000002 RSI: ffffffff8adef740 RDI: ffffffff8adef700
RBP: 1ffff1100eeead62 R08: dffffc0000000000 R09: fffffbfff1c3ed56
R10: fffffbfff1c3ed56 R11: 1ffffffff1c3ed55 R12: ffff88807c108054
R13: dffffc0000000000 R14: ffff888077756b10 R15: ffff88807c108000
rcu_read_unlock include/linux/rcupdate.h:823 [inline]
get_mem_cgroup_from_objcg+0x12d/0x150 include/linux/memcontrol.h:525
obj_cgroup_charge_pages mm/memcontrol.c:3097 [inline]
obj_cgroup_charge+0x342/0x610 mm/memcontrol.c:3390
memcg_slab_pre_alloc_hook mm/slab.h:501 [inline]
slab_pre_alloc_hook+0x2e7/0x310 mm/slab.h:715
slab_alloc_node mm/slub.c:3279 [inline]
__kmem_cache_alloc_node+0x4f/0x260 mm/slub.c:3398
kmalloc_trace+0x26/0xe0 mm/slab_common.c:1026
kmalloc include/linux/slab.h:563 [inline]
kzalloc include/linux/slab.h:699 [inline]
alloc_tty_struct+0xa6/0x740 drivers/tty/tty_io.c:3089
tty_init_dev+0x55/0x4c0 drivers/tty/tty_io.c:1408
ptmx_open+0xdb/0x2c0 drivers/tty/pty.c:824
chrdev_open+0x597/0x670 fs/char_dev.c:414
do_dentry_open+0x7e9/0x10d0 fs/open.c:882
do_open fs/namei.c:3634 [inline]
path_openat+0x25c6/0x2e70 fs/namei.c:3791
do_filp_open+0x1c1/0x3c0 fs/namei.c:3818
do_sys_openat2+0x142/0x490 fs/open.c:1318
do_sys_open fs/open.c:1334 [inline]
__do_sys_openat fs/open.c:1350 [inline]
__se_sys_openat fs/open.c:1345 [inline]
__x64_sys_openat+0x135/0x160 fs/open.c:1345
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: 0033:0x7ff02178f749
RSP: 002b:00007ff022597038 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007ff0219e5fa0 RCX: 00007ff02178f749
RDX: 0000000000082000 RSI: 00002000000013c0 RDI: ffffffffffffff9c
RBP: 00007ff021813f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff0219e6038 R14: 00007ff0219e5fa0 R15: 00007ffe4670d6b8
</TASK>
rcu: rcu_preempt kthread starved for 10543 jiffies! g8217 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:28096 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
preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6873
irqentry_exit+0x63/0x70 kernel/entry/common.c:439
asm_sysvec_reschedule_ipi+0x16/0x20 arch/x86/include/asm/idtentry.h:696
RIP: 0010:__timer_delete_sync+0x18d/0x2c0 kernel/time/timer.c:1563
Code: 65 10 00 49 89 dc 4d 85 f6 48 bb 00 00 00 00 00 fc ff df 75 07 e8 f3 64 10 00 eb 06 e8 ec 64 10 00 fb 65 44 8b 35 cb fd 91 7e <44> 89 f6 81 e6 00 00 0f 00 31 ff e8 33 68 10 00 41 81 e6 00 00 0f
RSP: 0018:ffffc90000157ae0 EFLAGS: 00000293
RAX: ffffffff81707174 RBX: dffffc0000000000 RCX: ffff88813fef5940
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000157bb0 R08: dffffc0000000000 R09: fffffbfff1c3ed56
R10: fffffbfff1c3ed56 R11: 1ffffffff1c3ed55 R12: ffffc90000157be0
R13: 1ffff9200002af60 R14: 0000000080000000 R15: 0000000000000000
timer_delete_sync kernel/time/timer.c:1628 [inline]
del_timer_sync include/linux/timer.h:200 [inline]
schedule_timeout+0x166/0x280 kernel/time/timer.c:2168
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:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:default_idle+0xb/0x10 arch/x86/kernel/process.c:742
Code: 48 89 df e8 b7 3b af f7 e9 4c ff ff ff e8 dd 07 f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 66 90 0f 00 2d 97 d4 64 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: b819be7058644600 RBX: ffffffff8a21ce97 RCX: b819be7058644600
RDX: 0000000000000001 RSI: ffffffff8a8c0580 RDI: ffffffff8adef760
RBP: ffffc90000177f20 R08: dffffc0000000000 R09: ffffed10171e6afa
R10: ffffed10171e6afa R11: 1ffff110171e6af9 R12: 0000000000000001
R13: dffffc0000000000 R14: ffff888017739dc0 R15: 1ffffffff1c3ed96
FS: 0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff022596f98 CR3: 000000005b535000 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+0x1fc/0x570 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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