Re: [syzbot] [kernel?] INFO: rcu detected stall in kthread (6)

[syzbot <syzbot+2d47e0896b84fae323c7@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    15ef2f78c49d Merge tag 'input-for-v7.2-rc7' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1279c279580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1d67342c314f228d
dashboard link: https://syzkaller.appspot.com/bug?extid=2d47e0896b84fae323c7
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16de2a25580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11e6b279580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a93f43b69b22/disk-15ef2f78.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d4fdb6da0cae/vmlinux-15ef2f78.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ef548cd2e0c1/bzImage-15ef2f78.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2d47e0896b84fae323c7@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	(detected by 0, t=10502 jiffies, g=13061, q=1051 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10500 (4294955331-4294944831), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10500 jiffies! g13061 f0x2 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:27592 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x125c/0x6730 kernel/sched/core.c:7234
 preempt_schedule_irq+0x50/0x90 kernel/sched/core.c:7556
 irqentry_exit_to_kernel_mode_preempt include/linux/irq-entry-common.h:468 [inline]
 irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:539 [inline]
 irqentry_exit+0x205/0xa00 kernel/entry/common.c:167
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:rcu_gp_fqs_loop+0x1a9/0x900 kernel/rcu/tree.c:2123
Code: f6 c5 02 75 42 48 8b 05 fd fc ef 0c 48 85 c0 75 0c 48 8b 05 71 fd ef 0c 48 85 c0 74 2a 48 85 db 74 25 48 89 df e8 87 23 d0 09 <48> 89 c3 ba 02 04 00 00 4c 89 ee 48 c7 c7 98 3a df 8e e8 50 6b f3
RSP: 0018:ffffc90000157ca8 EFLAGS: 00000282
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
RDX: ffff88801f280000 RSI: ffffffff8bbf5da1 RDI: ffffffff8c600380
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8ea0f280
R13: ffffc90000157d10 R14: 0000000000000000 R15: 1ffff9200002af96
 rcu_gp_kthread+0x179/0x230 kernel/rcu/tree.c:2325
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 UID: 0 PID: 5954 Comm: syz.0.26 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:188 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x29/0x50 kernel/locking/spinlock.c:206
Code: 90 f3 0f 1e fa 53 48 8b 74 24 08 48 89 fb 48 83 c7 18 e8 fa 90 26 f6 48 89 df e8 82 e0 26 f6 e8 fd 49 53 f6 fb bf 01 00 00 00 <e8> 32 ee 15 f6 65 8b 05 5b a7 c4 08 85 c0 74 06 5b e9 81 4b 00 00
RSP: 0018:ffffc9000202fc88 EFLAGS: 00000206
RAX: 000000000515ac11 RBX: ffff88802e28ef00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8e3aced0 RDI: 0000000000000001
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000021
R13: ffff88802e28f300 R14: dffffc0000000000 R15: ffff888021f3a540
FS:  00007f8b813fb6c0(0000) GS:ffff888123bde000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000058 CR3: 0000000078326000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 spin_unlock_irq include/linux/spinlock.h:402 [inline]
 get_signal+0x195a/0x21e0 kernel/signal.c:3049
 arch_do_signal_or_restart+0x91/0x7e0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
 exit_to_user_mode_loop+0x139/0x6f0 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 do_syscall_64+0x666/0x870 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8b8059e0d7
Code: 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89
RSP: 002b:00007f8b813fb0e8 EFLAGS: 00000246
RAX: 00000000000000ca RBX: 00007f8b80825fa8 RCX: 00007f8b8059e0d9
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f8b80825fa8
RBP: 00007f8b80825fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8b80826038 R14: 00007fff1b59f550 R15: 00007fff1b59f638
 </TASK>


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