rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P4271/1:b..l
(detected by 1, t=10502 jiffies, g=23105, q=80)
task:kworker/u4:5 state:R running task stack:22288 pid: 4271 ppid: 2 flags:0x00004000
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
preempt_schedule_notrace+0xd9/0x120 kernel/sched/core.c:6650
preempt_schedule_notrace_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:35
rcu_is_watching+0x72/0xa0 kernel/rcu/tree.c:1124
trace_lock_acquire include/trace/events/lock.h:13 [inline]
lock_acquire+0xc8/0x400 kernel/locking/lockdep.c:5594
rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:313
rcu_read_lock include/linux/rcupdate.h:740 [inline]
percpu_ref_put_many include/linux/percpu-refcount.h:317 [inline]
percpu_ref_put include/linux/percpu-refcount.h:338 [inline]
blk_mq_sched_insert_requests+0x32e/0x5c0 block/blk-mq-sched.c:521
blk_mq_flush_plug_list+0x59b/0x690 block/blk-mq.c:1971
blk_flush_plug_list+0x404/0x450 block/blk-core.c:1734
blk_schedule_flush_plug include/linux/blkdev.h:1235 [inline]
io_schedule_prepare kernel/sched/core.c:8471 [inline]
io_schedule+0x74/0xd0 kernel/sched/core.c:8502
rq_qos_wait+0x21d/0x2f0 block/blk-rq-qos.c:288
__wbt_wait block/blk-wbt.c:522 [inline]
wbt_wait+0x38e/0x680 block/blk-wbt.c:586
__rq_qos_throttle+0x61/0xa0 block/blk-rq-qos.c:72
rq_qos_throttle block/blk-rq-qos.h:203 [inline]
blk_mq_submit_bio+0x430/0x1820 block/blk-mq.c:2232
__submit_bio+0x7d1/0x820 block/blk-core.c:917
__submit_bio_noacct_mq block/blk-core.c:997 [inline]
submit_bio_noacct+0x6b0/0x800 block/blk-core.c:1027
submit_bio+0x2c1/0x560 block/blk-core.c:1089
ext4_io_submit fs/ext4/page-io.c:381 [inline]
io_submit_add_bh fs/ext4/page-io.c:425 [inline]
ext4_bio_write_page+0x1548/0x1f90 fs/ext4/page-io.c:564
mpage_submit_page+0x17a/0x210 fs/ext4/inode.c:2113
mpage_process_page_bufs+0x6d8/0x8b0 fs/ext4/inode.c:2227
mpage_prepare_extent_to_map+0xbc2/0xfe0 fs/ext4/inode.c:2655
ext4_writepages+0xa9a/0x2df0 fs/ext4/inode.c:2783
do_writepages+0x476/0x6e0 mm/page-writeback.c:2386
__writeback_single_inode+0x153/0xda0 fs/fs-writeback.c:1657
writeback_sb_inodes+0xa4e/0x1680 fs/fs-writeback.c:1940
__writeback_inodes_wb+0x12a/0x3f0 fs/fs-writeback.c:2011
wb_writeback+0x46f/0xbe0 fs/fs-writeback.c:2116
wb_check_old_data_flush fs/fs-writeback.c:2216 [inline]
wb_do_writeback fs/fs-writeback.c:2269 [inline]
wb_workfn+0xb15/0xf20 fs/fs-writeback.c:2298
process_one_work+0x85f/0x1010 kernel/workqueue.c:2310
worker_thread+0xaa6/0x1290 kernel/workqueue.c:2457
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
rcu: rcu_preempt kthread starved for 10562 jiffies! g23105 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:27536 pid: 15 ppid: 2 flags:0x00004000
Call Trace:
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:1914
rcu_gp_fqs_loop+0x2be/0x11d0 kernel/rcu/tree.c:1972
rcu_gp_kthread+0x9b/0x370 kernel/rcu/tree.c:2145
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
rcu: Stack dump where RCU GP kthread last ran:
NMI backtrace for cpu 1
CPU: 1 PID: 7068 Comm: syz.4.844 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
nmi_cpu_backtrace+0x3a2/0x3d0 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+0x1110/0x1270 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+0x843/0x1120 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+0x4ad/0xb70 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
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:lock_acquire+0x208/0x400 kernel/locking/lockdep.c:5627
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3d 04 f8 0f 85 f1 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:ffffc900034cfb60 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: e30bb89399977400
RDX: 0000000000000000 RSI: ffffffff8a2b2ea0 RDI: ffffffff8a79e740
RBP: ffffc900034cfc80 R08: dffffc0000000000 R09: 1ffffffff2036e1e
R10: dffffc0000000000 R11: fffffbfff2036e1f R12: ffff88807bfeea28
R13: 1ffff92000699f78 R14: 0000000000000246 R15: dffffc0000000000
__might_fault+0xb3/0x110 mm/memory.c:5357
_copy_from_user+0x29/0x170 lib/usercopy.c:14
copy_from_user include/linux/uaccess.h:192 [inline]
restore_sigcontext arch/x86/kernel/signal.c:91 [inline]
__ia32_sys_rt_sigreturn+0x21d/0x760 arch/x86/kernel/signal.c:674
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f8c6aaa80d9
Code: 11 06 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 90 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 c7 c0 0f 00 00 00 0f 05 <0f> 1f 80 00 00 00 00 48 81 ec 48 01 00 00 49 89 d0 64 48 8b 0c 25
RSP: 002b:00007f8c68d61a80 EFLAGS: 00000202 ORIG_RAX: 000000000000000f
RAX: ffffffffffffffda RBX: 00007f8c6ad81fa0 RCX: 00007f8c6aaa80d9
RDX: 00007f8c68d61a80 RSI: 00007f8c68d61bb0 RDI: 0000000000000021
RBP: 00007f8c6ab74bf7 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 00007f8c6ad82038 R14: 00007f8c6ad81fa0 R15: 00007fffabd0e868