[v6.1] INFO: rcu detected stall in sys_getpid (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c27210688955 Linux 6.1.173
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1297647e580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0605c5af04d7603
dashboard link: https://syzkaller.appspot.com/bug?extid=51bc0c08938dfe165e48
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/92fbc0595a58/disk-c2721068.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0f281a0d62f7/vmlinux-c2721068.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b17a33c5f1fe/bzImage-c2721068.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+51bc0c...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P4536/1:b..l
(detected by 0, t=10502 jiffies, g=9905, q=380 ncpus=2)
task:syz.1.66 state:R running task stack:25424 pid:4536 ppid:4270 flags:0x00004000
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:lock_acquire+0x225/0x4a0 kernel/locking/lockdep.c:5666
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3d 04 f8 0f 85 f0 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 43 c7 44 3d 08 00 00 00 00 65 48 8b 04
RSP: 0018:ffffc90004cdfda0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 4570ee55a47c9b00
RDX: 0000000000000000 RSI: ffffffff8a8c2b20 RDI: ffffffff8adf1ba0
RBP: ffffc90004cdfec0 R08: dffffc0000000000 R09: 1ffffffff215f448
R10: dffffc0000000000 R11: fffffbfff215f449 R12: 0000000000000000
R13: 1ffff9200099bfc0 R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
rcu_read_lock include/linux/rcupdate.h:791 [inline]
__task_pid_nr_ns+0x44/0x460 kernel/pid.c:497
task_tgid_vnr include/linux/sched.h:1631 [inline]
__ia32_sys_getpid+0x19/0x20 kernel/sys.c:953
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: 0033:0x7fae1eb96bd7
RSP: 002b:00007ffeb8c73848 EFLAGS: 00000206 ORIG_RAX: 0000000000000027
RAX: ffffffffffffffda RBX: 00007ffeb8c739b0 RCX: 00007fae1eb96bd7
RDX: 00007ffeb8c73880 RSI: 00007ffeb8c739b0 RDI: 0000000000000021
RBP: 0000000000000000 R08: 00007fae1ee00000 R09: 00007fae1ee02000
R10: 0000000081bf42d8 R11: 0000000000000206 R12: 00007fae1ee16128
R13: 0000000000008c6e R14: ffffffff81dddca5 R15: 00007fae1f945720
</TASK>
rcu: rcu_preempt kthread starved for 10147 jiffies! g9905 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:27632 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:
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


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