Kernel bug: INFO: rcu detected stall in wb_workfn (4)
Subsystem: mm
Status: open

Crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-...!: (1 GPs behind) idle=591c/1/0x4000000000000000 softirq=16719/16748 fqs=0
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P6037/1:b..l
rcu: 	(detected by 1, t=10508 jiffies, g=9837, q=1119 ncpus=2)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 1110 Comm: kworker/u8:6 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: writeback wb_workfn (flush-8:0)
RIP: 0010:rcu_preempt_read_exit kernel/rcu/tree_plugin.h:396 [inline]
RIP: 0010:__rcu_read_unlock+0x30/0x550 kernel/rcu/tree_plugin.h:435
Code: 41 55 41 54 55 65 48 8b 2d 15 c3 fe 11 53 48 8d bd 84 04 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6 14 02 <48> 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 4a 02 00 00 65
RSP: 0018:ffffc90000007d60 EFLAGS: 00000803
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffc90000007d54
RDX: 0000000000000000 RSI: ffffffff8da06705 RDI: ffff8880280ca904
RBP: ffff8880280ca480 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 1879d6bc4baa8f14
R13: 1879d6bc4baa8f14 R14: 0000000000000002 R15: ffff888060b17410
FS:  0000000000000000(0000) GS:ffff888124a05000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff7e1dfeb30 CR3: 0000000063c7a000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 rcu_read_unlock include/linux/rcupdate.h:899 [inline]
 advance_sched+0x6f6/0xc80 net/sched/sch_taprio.c:992
 __run_hrtimer kernel/time/hrtimer.c:1777 [inline]
 __hrtimer_run_queues+0x202/0xad0 kernel/time/hrtimer.c:1841
 hrtimer_interrupt+0x397/0x8e0 kernel/time/hrtimer.c:1903
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1041 [inline]
 __sysvec_apic_timer_interrupt+0x10b/0x3f0 arch/x86/kernel/apic/apic.c:1058
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1052 [inline]
 sysvec_apic_timer_interrupt+0x9f/0xc0 arch/x86/kernel/apic/apic.c:1052
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:lock_acquire+0x62/0x350 kernel/locking/lockdep.c:5872
Code: e6 08 12 83 f8 07 0f 87 bc 02 00 00 89 c0 48 0f a3 05 22 4b e9 0e 0f 82 74 02 00 00 8b 35 9a 7b e9 0e 85 f6 0f 85 8d 00 00 00 <48> 8b 44 24 30 65 48 2b 05 39 e6 08 12 0f 85 c7 02 00 00 48 83 c4
RSP: 0018:ffffc90003e4edc0 EFLAGS: 00000206
RAX: 0000000000000046 RBX: ffffffff8e3c4760 RCX: 000000009b3c7088
RDX: 0000000000000000 RSI: ffffffff8da06705 RDI: ffffffff8bf073c0
RBP: 0000000000000002 R08: 2aa13fcde29573aa R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 rcu_read_lock include/linux/rcupdate.h:867 [inline]
 page_ref_add_unless.constprop.0+0x36/0x390 include/linux/page_ref.h:235
 folio_ref_add_unless include/linux/page_ref.h:248 [inline]
 folio_try_get include/linux/page_ref.h:264 [inline]
 find_get_entry mm/filemap.c:2082 [inline]
 filemap_get_folios_tag+0x1d5/0xae0 mm/filemap.c:2338
 mpage_map_and_submit_buffers+0x273/0xab0 fs/ext4/inode.c:2307
 mpage_map_and_submit_extent fs/ext4/inode.c:2514 [inline]
 ext4_do_writepages+0x2149/0x3cf0 fs/ext4/inode.c:2931
 ext4_writepages+0x37a/0x7d0 fs/ext4/inode.c:3025
 do_writepages+0x27a/0x600 mm/page-writeback.c:2604
 __writeback_single_inode+0x160/0xfb0 fs/fs-writeback.c:1719
 writeback_sb_inodes+0x60d/0xfa0 fs/fs-writeback.c:2015
 __writeback_inodes_wb+0xf8/0x2d0 fs/fs-writeback.c:2086
 wb_writeback+0x7f3/0xb70 fs/fs-writeback.c:2197
 wb_check_old_data_flush fs/fs-writeback.c:2301 [inline]
 wb_do_writeback fs/fs-writeback.c:2354 [inline]
 wb_workfn+0x8ca/0xbe0 fs/fs-writeback.c:2382
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
 process_scheduled_works kernel/workqueue.c:3346 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
task:kworker/1:6     state:R  running task     stack:28632 pid:6037  tgid:6037  ppid:2      task_flags:0x4208060 flags:0x00080000
Workqueue: events_power_efficient gc_worker
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5325 [inline]
 __schedule+0x1190/0x5de0 kernel/sched/core.c:6929
 preempt_schedule_irq+0x51/0x90 kernel/sched/core.c:7256
 irqentry_exit+0x36/0x90 kernel/entry/common.c:211
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:__seqprop_spinlock_sequence include/linux/seqlock.h:227 [inline]
RIP: 0010:nf_conntrack_get_ht include/net/netfilter/nf_conntrack.h:342 [inline]
RIP: 0010:gc_worker+0x2d5/0x16e0 net/netfilter/nf_conntrack_core.c:1548
Code: 00 00 48 c7 c7 68 c1 82 90 e8 d7 33 19 f8 9c 5b 81 e3 00 02 00 00 31 ff 48 89 de e8 55 54 3d f8 58 48 85 db 0f 85 d4 0f 00 00 <e8> d6 58 3d f8 8b 1d 60 32 03 07 41 89 dc 31 ff 41 83 e4 01 44 89
RSP: 0018:ffffc900031b7b48 EFLAGS: 00000293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff897f9a39
RDX: ffff888061812480 RSI: ffffffff897f9a48 RDI: 0000000000000007
RBP: ffffffff9af903ec R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff88814ca00000
R13: 0000000000040000 R14: dffffc0000000000 R15: 0000000000001770
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
 process_scheduled_works kernel/workqueue.c:3346 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
rcu: rcu_preempt kthread starved for 10508 jiffies! g9837 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:28024 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5325 [inline]
 __schedule+0x1190/0x5de0 kernel/sched/core.c:6929
 __schedule_loop kernel/sched/core.c:7011 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:7026
 schedule_timeout+0x123/0x290 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x1ea/0xaf0 kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x26d/0x380 kernel/rcu/tree.c:2285
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x675/0x7d0 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: 1 UID: 0 PID: 5931 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:csd_lock_wait kernel/smp.c:342 [inline]
RIP: 0010:smp_call_function_many_cond+0xe02/0x1600 kernel/smp.c:877
Code: 10 4c 89 74 24 10 49 89 d5 48 89 d5 48 89 54 24 18 49 c1 ed 03 83 e5 07 4d 01 e5 83 c5 03 e8 b5 0c 0c 00 f3 90 41 0f b6 45 00 <40> 38 c5 7c 08 84 c0 0f 85 e0 05 00 00 8b 43 08 31 ff 83 e0 01 41
RSP: 0018:ffffc900045ff6f8 EFLAGS: 00000293
RAX: 0000000000000000 RBX: ffff8880b8442840 RCX: ffffffff81b0db41
RDX: ffff888027d90000 RSI: ffffffff81b0db1b RDI: 0000000000000005
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: dffffc0000000000
R13: ffffed1017088509 R14: 0000000000000001 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888124b05000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f8b2c9b6ad8 CR3: 000000000e182000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 on_each_cpu_cond_mask+0x40/0x90 kernel/smp.c:1043
 __flush_tlb_multi arch/x86/include/asm/paravirt.h:91 [inline]
 flush_tlb_multi arch/x86/mm/tlb.c:1381 [inline]
 flush_tlb_mm_range+0x4a0/0x17a0 arch/x86/mm/tlb.c:1471
 tlb_flush arch/x86/include/asm/tlb.h:23 [inline]
 tlb_flush_mmu_tlbonly include/asm-generic/tlb.h:490 [inline]
 tlb_flush_mmu_tlbonly include/asm-generic/tlb.h:480 [inline]
 tlb_flush_mmu mm/mmu_gather.c:403 [inline]
 tlb_finish_mmu+0x3c9/0x7c0 mm/mmu_gather.c:497
 exit_mmap+0x3fc/0xb90 mm/mmap.c:1293
 __mmput+0x12a/0x410 kernel/fork.c:1133
 mmput+0x62/0x70 kernel/fork.c:1156
 exit_mm kernel/exit.c:582 [inline]
 do_exit+0x7c7/0x2bf0 kernel/exit.c:954
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1107
 get_signal+0x2671/0x26d0 kernel/signal.c:3034
 arch_do_signal_or_restart+0x8f/0x7c0 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x85/0x130 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x426/0xfa0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff7e1f85853
Code: Unable to access opcode bytes at 0x7ff7e1f85829.
RSP: 002b:00007fff27608928 EFLAGS: 00000202 ORIG_RAX: 000000000000003d
RAX: fffffffffffffe00 RBX: 000000000000172e RCX: 00007ff7e1f85853
RDX: 0000000040000000 RSI: 00007fff2760893c RDI: 00000000ffffffff
RBP: 00007fff2760893c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002
R13: 00007fff276089a8 R14: 00007fff27608c28 R15: 0000000000000000
 </TASK>
sched: DL replenish lagged too much