syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P9/1:b..l
	(detected by 1, t=10502 jiffies, g=8213, q=122)
task:kworker/u4:0    state:R  running task     stack:21352 pid:    9 ppid:     2 flags:0x00004000
Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
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:test_clear_page_writeback+0xaf2/0xd20 mm/page-writeback.c:2832
Code: e9 25 f7 ff ff e8 ae 2e d8 ff 48 ff cb e9 7e f7 ff ff e8 a1 2e d8 ff e8 dc 49 02 08 4d 85 f6 74 d0 e8 92 2e d8 ff fb 4c 89 e7 <be> 06 00 00 00 e8 24 9b 06 00 4c 89 e7 be 20 00 00 00 e8 27 9d 06
RSP: 0000:ffffc90000ce7900 EFLAGS: 00000293
RAX: ffffffff819f9d7e RBX: 0000000000000001 RCX: ffff88813fed0000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffea0001bff140
RBP: ffffc90000ce7a10 R08: dffffc0000000000 R09: fffffbfff1ff5433
R10: fffffbfff1ff5433 R11: 1ffffffff1ff5432 R12: ffffea0001bff140
R13: dffffc0000000000 R14: 0000000000000200 R15: 0000000000000000
 end_page_writeback+0x282/0x660 mm/filemap.c:1603
 ext4_finish_bio+0x747/0x8b0 fs/ext4/page-io.c:145
 ext4_release_io_end+0xef/0x2c0 fs/ext4/page-io.c:160
 ext4_end_io_end fs/ext4/page-io.c:194 [inline]
 ext4_do_flush_completed_IO fs/ext4/page-io.c:259 [inline]
 ext4_end_io_rsv_work+0x4ee/0x600 fs/ext4/page-io.c:273
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: rcu_preempt kthread starved for 10533 jiffies! g8213 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: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
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:1914
 rcu_gp_fqs_loop+0x29e/0x11b0 kernel/rcu/tree.c:1972
 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:
NMI backtrace for cpu 1
CPU: 1 PID: 4450 Comm: syz.4.21 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x397/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
 rcu_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487
 print_other_cpu_stall+0x10c8/0x1220 kernel/rcu/tree_stall.h:592
 check_cpu_stall kernel/rcu/tree_stall.h:745 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x831/0x1110 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:1818
 tick_sched_handle kernel/time/tick-sched.c:254 [inline]
 tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4fe/0xc40 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x3bb/0x8d0 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
 __sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0x9b/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:__syscall_enter_from_user_work kernel/entry/common.c:93 [inline]
RIP: 0010:syscall_enter_from_user_mode+0x2a/0x70 kernel/entry/common.c:114
Code: 41 56 53 48 89 f3 49 89 fe 48 8b 7c 24 10 e8 3d f6 ff ff eb 31 eb 35 e8 74 f9 db f7 e8 6f f7 db f7 fb 65 48 8b 05 36 7d 60 76 <48> 8b 70 08 40 f6 c6 3f 74 0b 4c 89 f7 5b 41 5e e9 21 3b c4 f7 48
RSP: 0018:ffffc90004157f08 EFLAGS: 00000286
RAX: ffff8880279b8000 RBX: 0000000000000027 RCX: e191469a81c16100
RDX: dffffc0000000000 RSI: ffffffff8a0b1be0 RDI: ffffffff8a59e800
RBP: ffffc90004157f48 R08: dffffc0000000000 R09: fffffbfff1ad26b6
R10: fffffbfff1ad26b6 R11: 1ffffffff1ad26b5 R12: 0000000000000000
R13: 0000000000000000 R14: ffffc90004157f58 R15: 0000000000000000
 do_syscall_64+0x24/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fe6f53b65e7
Code: 0b e9 68 fe ff ff 48 83 c4 18 48 8d 3d b2 62 d9 00 5b 5d 41 5c 41 5d 41 5e 41 5f e9 23 f8 fb ff 0f 1f 00 b8 27 00 00 00 0f 05 <c3> 0f 1f 84 00 00 00 00 00 b8 6e 00 00 00 0f 05 c3 0f 1f 84 00 00
RSP: 002b:00007fffdebb2748 EFLAGS: 00000206 ORIG_RAX: 0000000000000027
RAX: ffffffffffffffda RBX: 00007fffdebb28b0 RCX: 00007fe6f53b65e7
RDX: 00007fffdebb2780 RSI: 00007fffdebb28b0 RDI: 0000000000000021
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007fe6f5615fa0 R14: 00007fe6f5615fa0 R15: 0000000000000004
 </TASK>