[v5.15] INFO: rcu detected stall in kthread (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 68efe5a6c16a Linux 5.15.197
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1393a1c2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7e6ed99963d6ee1d
dashboard link: https://syzkaller.appspot.com/bug?extid=58a9f6b2a89c586d0fef
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/900f9b9bd850/disk-68efe5a6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1e089a5019a6/vmlinux-68efe5a6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b319f477b907/bzImage-68efe5a6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+58a9f6...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
(detected by 1, t=10502 jiffies, g=12181, q=172)
rcu: All QSes seen, last rcu_preempt kthread activity 10502 (4294959200-4294948698), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10502 jiffies! g12181 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I stack:28064 pid: 15 ppid: 2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11bb/0x4390 kernel/sched/core.c:6395
preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6799
irqentry_exit+0x63/0x70 kernel/entry/common.c:432
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:rcu_gp_fqs_loop+0x2aa/0x11b0 kernel/rcu/tree.c:1972
Code: 93 51 ad 0a 00 75 0a 48 83 3d 09 52 ad 0a 00 74 12 48 85 db 74 0d 48 89 df e8 22 4e 46 08 48 89 c3 eb ad 48 c7 c7 e0 0f 12 8c <48> 8d b4 24 c0 00 00 00 e8 e9 9a f4 ff 48 ba 00 00 00 00 00 fc ff
RSP: 0018:ffffc90000d47cc0 EFLAGS: 00000202
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff8a0b1be0 RDI: ffffffff8c120fe0
RBP: ffffc90000d47e10 R08: dffffc0000000000 R09: fffffbfff18241fd
R10: fffffbfff18241fd R11: 1ffffffff18241fc R12: 1ffffffff17c1e30
R13: ffffc90000d47d88 R14: 0000000000000002 R15: 0000000000000001
rcu_gp_kthread+0x98/0x350 kernel/rcu/tree.c:2145
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4775 Comm: syz.2.115 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:check_kcov_mode kernel/kcov.c:183 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:227 [inline]
RIP: 0010:__sanitizer_cov_trace_switch+0x89/0xe0 kernel/kcov.c:329
Code: 44 8b 1d f2 9e 8a 7e 41 81 e3 00 01 ff 00 74 13 41 81 fb 00 01 00 00 75 d9 41 83 b8 34 16 00 00 00 74 cf 45 8b 98 10 16 00 00 <41> 83 fb 03 75 c2 4d 8b 98 18 16 00 00 45 8b b8 14 16 00 00 49 c1
RSP: 0018:ffffc9000343fa48 EFLAGS: 00000046
RAX: 0000000000000002 RBX: ffff8880b9027280 RCX: 0000000000000005
RDX: ffffffff816a8f09 RSI: ffffffff8c136460 RDI: 0000000000000003
RBP: 0000000000000001 R08: ffff8880295e3b80 R09: 0000000000000001
R10: 0000000000000003 R11: 0000000000000002 R12: dffffc0000000000
R13: ffff8880737fe980 R14: 000000337a481fff R15: 0000000000000003
FS: 00007f126c21b6c0(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000058 CR3: 0000000019de9000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
clockevents_program_event+0x79/0x310 kernel/time/clockevents.c:315
hrtimer_start_range_ns+0xa9a/0xc20 kernel/time/hrtimer.c:1287
posixtimer_rearm+0x131/0x340 kernel/time/posix-timers.c:329
dequeue_signal+0x174/0x440 kernel/signal.c:696
get_signal+0x6fe/0x12c0 kernel/signal.c:2781
arch_do_signal_or_restart+0xc1/0x1300 arch/x86/kernel/signal.c:867
handle_signal_work kernel/entry/common.c:154 [inline]
exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
__syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f126dfb4747
Code: ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 <0f> 05 48 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89
RSP: 002b:00007f126c21b038 EFLAGS: 00000246
RAX: 0000000000000049 RBX: 00007f126e20afa0 RCX: 00007f126dfb4749
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000004
RBP: 00007f126e038f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f126e20b038 R14: 00007f126e20afa0 R15: 00007fffa30faae8
</TASK>


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