INFO: rcu detected stall in kernfs_fop_write_iter (2)

Status: upstream: reported on 2026/05/04 00:10
Reported-by: syzbot+c6125376af0a7bcd9d92@syzkaller.appspotmail.com
First crash: 97d, last: 97d
▶ ▼ Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in kernfs_fop_write_iter (2) net mm 1 4 471d 632d 0/29 auto-obsoleted due to no activity on 2025/07/23 14:56
linux-6.1 INFO: rcu detected stall in kernfs_fop_write_iter (4) 1 2 152d 220d 0/3 auto-obsoleted due to no activity on 2026/06/17 16:43
linux-5.15 INFO: rcu detected stall in kernfs_fop_write_iter 1 1 649d 649d 0/3 auto-obsoleted due to no activity on 2025/02/05 10:26
upstream INFO: rcu detected stall in kernfs_fop_write_iter (3) prio:low net 1 syz error error 24 29d 213d 0/29 upstream: reported syz repro on 2026/01/07 17:45
linux-6.1 INFO: rcu detected stall in kernfs_fop_write_iter (2) 1 2 733d 830d 0/3 auto-obsoleted due to no activity on 2024/11/14 04:13
linux-6.1 INFO: rcu detected stall in kernfs_fop_write_iter (3) 1 1 332d 332d 0/3 auto-obsoleted due to no activity on 2025/12/19 09:23
upstream INFO: rcu detected stall in kernfs_fop_write_iter fs sctp 1 7 726d 821d 0/29 auto-obsoleted due to no activity on 2024/11/10 20:48
linux-6.1 INFO: rcu detected stall in kernfs_fop_write_iter 1 1 1109d 1109d 0/3 auto-obsoleted due to no activity on 2023/11/03 22:13
android-6-1 BUG: soft lockup in kernfs_fop_write_iter 1 1 453d 453d 0/2 auto-obsoleted due to no activity on 2025/08/11 05:47

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	0-...!: (6 ticks this GP) idle=217/1/0x4000000000000002 softirq=18556/18556 fqs=0 
	(detected by 1, t=10502 jiffies, g=24329, q=343)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 8058 Comm: syz.0.864 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:unwind_next_frame+0x1582/0x1d90 arch/x86/kernel/unwind_orc.c:626
Code: b8 00 00 00 00 00 fc ff df 48 8b 4c 24 48 0f b6 04 01 84 c0 0f 85 df 01 00 00 c7 03 00 00 00 00 31 c0 48 81 c4 88 00 00 00 5b <41> 5c 41 5d 41 5e 41 5f 5d c3 49 c7 c5 a8 da 94 8d 4c 89 e0 4c 29
RSP: 0018:ffffc90000007110 EFLAGS: 00000082
RAX: 0000000000000101 RBX: ffffc90000007200 RCX: 0000000000000102
RDX: ffffc90000007201 RSI: ffffc900000074b0 RDI: 00000000ffffffff
RBP: ffffc90000007248 R08: ffffc9000000725f R09: ffffc90000007250
R10: dffffc0000000000 R11: fffff52000000e4c R12: ffffc90000000000
R13: dffffc0000000000 R14: ffffc90000007210 R15: ffffc900000074c0
FS:  00007f86e73d96c0(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000ee00000000 CR3: 00000000689ec000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 __unwind_start+0x5bb/0x740 arch/x86/kernel/unwind_orc.c:704
 unwind_start arch/x86/include/asm/unwind.h:60 [inline]
 perf_callchain_kernel+0x2f0/0x720 arch/x86/events/core.c:-1
 get_perf_callchain+0x356/0x460 kernel/events/callchain.c:200
 perf_callchain kernel/events/core.c:7606 [inline]
 perf_prepare_sample+0x352/0x1cd0 kernel/events/core.c:7633
 __perf_event_output kernel/events/core.c:7802 [inline]
 perf_event_output_forward+0x185/0x2e0 kernel/events/core.c:7822
 __perf_event_overflow+0x364/0x530 kernel/events/core.c:9515
 perf_tp_event+0x383/0xbf0 kernel/events/core.c:10047
 perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10021
 perf_trace_preemptirq_template+0x2aa/0x360 include/trace/events/preemptirq.h:14
 trace_irq_enable_rcuidle+0x108/0x180 include/trace/events/preemptirq.h:40
 trace_hardirqs_on+0x57/0x80 kernel/trace/trace_preemptirq.c:44
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x7f/0x4a0 kernel/rcu/tree_plugin.h:674
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 32 e1 9c 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc90000007b00 EFLAGS: 00000206
RAX: 7b373c8db71d6900 RBX: 1ffff92000000f64 RCX: 7b373c8db71d6900
RDX: dffffc0000000000 RSI: ffffffff8a2b2800 RDI: ffffffff8a79fe00
RBP: ffffc90000007bd8 R08: ffffffff901d50df R09: 1ffffffff203aa1b
R10: dffffc0000000000 R11: fffffbfff203aa1c R12: ffffffff8c323000
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 ieee80211_iterate_active_interfaces_atomic+0x132/0x140 net/mac80211/util.c:831
 mac80211_hwsim_beacon+0x9b/0x180 drivers/net/wireless/mac80211_hwsim.c:1865
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4f2/0xb70 kernel/time/hrtimer.c:1749
 hrtimer_run_softirq+0x176/0x240 kernel/time/hrtimer.c:1766
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 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:finish_lock_switch+0x134/0x280 kernel/sched/core.c:4804
Code: be ff ff ff ff e8 3c 52 68 08 85 c0 74 4a 4d 85 ff 75 66 0f 1f 44 00 00 48 89 df e8 e6 bd 71 08 e8 61 e6 2a 00 fb 48 83 c4 08 <5b> 41 5c 41 5d 41 5e 41 5f 5d c3 48 89 df e8 c9 09 fe ff 43 80 3c
RSP: 0018:ffffc900030ff268 EFLAGS: 00000282
RAX: 7b373c8db71d6900 RBX: ffff8880b903a340 RCX: 7b373c8db71d6900
RDX: dffffc0000000000 RSI: ffffffff8a2b2800 RDI: ffffffff8a79fe00
RBP: 1ffff11017207613 R08: ffffffff901d50df R09: 1ffffffff203aa1b
R10: dffffc0000000000 R11: fffffbfff203aa1c R12: 1ffff110172075c1
R13: dffffc0000000000 R14: ffff8880b903ae08 R15: 0000000000000000
 finish_task_switch+0x12f/0x640 kernel/sched/core.c:4921
 context_switch kernel/sched/core.c:5052 [inline]
 __schedule+0x11f7/0x43c0 kernel/sched/core.c:6395
 preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6571
 preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6596
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
 _raw_spin_unlock_irqrestore+0x10d/0x120 kernel/locking/spinlock.c:194
 rcu_report_exp_rnp kernel/rcu/tree_exp.h:223 [inline]
 rcu_preempt_deferred_qs_irqrestore+0x88b/0xc30 kernel/rcu/tree_plugin.h:562
 rcu_read_unlock_special+0x3dd/0x4a0 kernel/rcu/tree_plugin.h:673
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 dl_rebuild_rd_accounting kernel/cgroup/cpuset.c:1027 [inline]
 partition_and_rebuild_sched_domains kernel/cgroup/cpuset.c:1043 [inline]
 rebuild_sched_domains_locked+0x1c4a/0x2040 kernel/cgroup/cpuset.c:1107
 update_cpumask kernel/cgroup/cpuset.c:1669 [inline]
 cpuset_write_resmask+0x9eb/0x1390 kernel/cgroup/cpuset.c:2553
 cgroup_file_write+0x2c3/0x660 kernel/cgroup/cgroup.c:3967
 kernfs_fop_write_iter+0x379/0x4c0 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2173 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x745/0xd60 fs/read_write.c:594
 ksys_write+0x152/0x260 fs/read_write.c:647
 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: 0033:0x7f86e917fdd9
Code: 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 01 48
RSP: 002b:00007f86e73d9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f86e93f8fa0 RCX: 00007f86e917fdd9
RDX: 0000000000000031 RSI: 0000200000000240 RDI: 0000000000000005
RBP: 00007f86e9215d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f86e93f9038 R14: 00007f86e93f8fa0 R15: 00007ffea4971528
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10501 jiffies! g24329 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=0 timer-softirq=12032
rcu: rcu_preempt kthread starved for 10502 jiffies! g24329 f0x0 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:26928 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 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:2117
 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
 </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: 8058 Comm: syz.0.864 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:rcu_lockdep_current_cpu_online+0x30/0x130 kernel/rcu/tree.c:1171
Code: 53 65 8b 0d 3a 8e 9d 7e b0 01 f7 c1 00 00 f0 00 0f 85 e2 00 00 00 83 3d a5 0f 25 0c 00 0f 84 d5 00 00 00 65 ff 05 18 8e 9d 7e <e8> fb f7 57 08 89 c3 83 f8 08 0f 83 cd 00 00 00 49 bf 00 00 00 00
RSP: 0018:ffffc90000007360 EFLAGS: 00000006
RAX: 0000000000008201 RBX: 0000000000000000 RCX: 0000000000000102
RDX: 0000000000000100 RSI: ffffffff8a79fde0 RDI: ffffffff8a79fda0
RBP: 0000000000000001 R08: ffffc90000007537 R09: ffffc90000007500
R10: dffffc0000000000 R11: fffff52000000ea7 R12: dffffc0000000000
R13: ffffc90000007566 R14: ffffffff8c125da0 R15: dffffc0000000000
FS:  00007f86e73d96c0(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000ee00000000 CR3: 00000000689ec000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 rcu_read_lock_held_common kernel/rcu/update.c:112 [inline]
 rcu_read_lock_held+0x1a/0x40 kernel/rcu/update.c:309
 perf_get_guest_cbs include/linux/perf_event.h:1274 [inline]
 perf_misc_flags+0x56/0x1b0 arch/x86/events/core.c:2961
 perf_prepare_sample+0x132/0x1cd0 kernel/events/core.c:7622
 __perf_event_output kernel/events/core.c:7802 [inline]
 perf_event_output_forward+0x185/0x2e0 kernel/events/core.c:7822
 __perf_event_overflow+0x364/0x530 kernel/events/core.c:9515
 perf_tp_event+0x383/0xbf0 kernel/events/core.c:10047
 perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10021
 perf_trace_preemptirq_template+0x2aa/0x360 include/trace/events/preemptirq.h:14
 trace_irq_enable_rcuidle+0x108/0x180 include/trace/events/preemptirq.h:40
 trace_hardirqs_on+0x57/0x80 kernel/trace/trace_preemptirq.c:44
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x7f/0x4a0 kernel/rcu/tree_plugin.h:674
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 32 e1 9c 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc90000007b00 EFLAGS: 00000206
RAX: 7b373c8db71d6900 RBX: 1ffff92000000f64 RCX: 7b373c8db71d6900
RDX: dffffc0000000000 RSI: ffffffff8a2b2800 RDI: ffffffff8a79fe00
RBP: ffffc90000007bd8 R08: ffffffff901d50df R09: 1ffffffff203aa1b
R10: dffffc0000000000 R11: fffffbfff203aa1c R12: ffffffff8c323000
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 ieee80211_iterate_active_interfaces_atomic+0x132/0x140 net/mac80211/util.c:831
 mac80211_hwsim_beacon+0x9b/0x180 drivers/net/wireless/mac80211_hwsim.c:1865
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4f2/0xb70 kernel/time/hrtimer.c:1749
 hrtimer_run_softirq+0x176/0x240 kernel/time/hrtimer.c:1766
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 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:finish_lock_switch+0x134/0x280 kernel/sched/core.c:4804
Code: be ff ff ff ff e8 3c 52 68 08 85 c0 74 4a 4d 85 ff 75 66 0f 1f 44 00 00 48 89 df e8 e6 bd 71 08 e8 61 e6 2a 00 fb 48 83 c4 08 <5b> 41 5c 41 5d 41 5e 41 5f 5d c3 48 89 df e8 c9 09 fe ff 43 80 3c
RSP: 0018:ffffc900030ff268 EFLAGS: 00000282
RAX: 7b373c8db71d6900 RBX: ffff8880b903a340 RCX: 7b373c8db71d6900
RDX: dffffc0000000000 RSI: ffffffff8a2b2800 RDI: ffffffff8a79fe00
RBP: 1ffff11017207613 R08: ffffffff901d50df R09: 1ffffffff203aa1b
R10: dffffc0000000000 R11: fffffbfff203aa1c R12: 1ffff110172075c1
R13: dffffc0000000000 R14: ffff8880b903ae08 R15: 0000000000000000
 finish_task_switch+0x12f/0x640 kernel/sched/core.c:4921
 context_switch kernel/sched/core.c:5052 [inline]
 __schedule+0x11f7/0x43c0 kernel/sched/core.c:6395
 preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6571
 preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6596
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
 _raw_spin_unlock_irqrestore+0x10d/0x120 kernel/locking/spinlock.c:194
 rcu_report_exp_rnp kernel/rcu/tree_exp.h:223 [inline]
 rcu_preempt_deferred_qs_irqrestore+0x88b/0xc30 kernel/rcu/tree_plugin.h:562
 rcu_read_unlock_special+0x3dd/0x4a0 kernel/rcu/tree_plugin.h:673
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 dl_rebuild_rd_accounting kernel/cgroup/cpuset.c:1027 [inline]
 partition_and_rebuild_sched_domains kernel/cgroup/cpuset.c:1043 [inline]
 rebuild_sched_domains_locked+0x1c4a/0x2040 kernel/cgroup/cpuset.c:1107
 update_cpumask kernel/cgroup/cpuset.c:1669 [inline]
 cpuset_write_resmask+0x9eb/0x1390 kernel/cgroup/cpuset.c:2553
 cgroup_file_write+0x2c3/0x660 kernel/cgroup/cgroup.c:3967
 kernfs_fop_write_iter+0x379/0x4c0 fs/kernfs/file.c:296
 call_write_iter include/linux/fs.h:2173 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x745/0xd60 fs/read_write.c:594
 ksys_write+0x152/0x260 fs/read_write.c:647
 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: 0033:0x7f86e917fdd9
Code: 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 01 48
RSP: 002b:00007f86e73d9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f86e93f8fa0 RCX: 00007f86e917fdd9
RDX: 0000000000000031 RSI: 0000200000000240 RDI: 0000000000000005
RBP: 00007f86e9215d69 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f86e93f9038 R14: 00007f86e93f8fa0 R15: 00007ffea4971528
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/04 00:09 linux-5.15.y ef251c45f1cd a0d91488 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in kernfs_fop_write_iter
* Struck through repros no longer work on HEAD.