syzbot


INFO: rcu detected stall in kernfs_fop_write_iter (4)

Status: upstream: reported on 2026/01/01 07:33
Reported-by: syzbot+5df2496a43a2ddc49e28@syzkaller.appspotmail.com
First crash: 77d, last: 10d
Similar bugs (8)
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 329d 489d 0/29 auto-obsoleted due to no activity on 2025/07/23 14:56
linux-5.15 INFO: rcu detected stall in kernfs_fop_write_iter 1 1 507d 507d 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) net 1 syz error error 17 48d 71d 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 590d 688d 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 190d 190d 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 584d 679d 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 967d 967d 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 310d 310d 0/2 auto-obsoleted due to no activity on 2025/08/11 05:47

Sample crash report:
rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 1-.... } 2657 jiffies s: 15645 root: 0x2/.
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 8979 Comm: syz.3.1439 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:native_save_fl arch/x86/include/asm/irqflags.h:36 [inline]
RIP: 0010:arch_local_save_flags arch/x86/include/asm/irqflags.h:70 [inline]
RIP: 0010:arch_irqs_disabled arch/x86/include/asm/irqflags.h:130 [inline]
RIP: 0010:lock_release+0x58f/0x920 kernel/locking/lockdep.c:5685
Code: 83 f8 01 75 7f 43 c6 44 2f 04 00 48 c7 84 24 80 00 00 00 00 00 00 00 9c 8f 84 24 80 00 00 00 f7 84 24 80 00 00 00 00 02 00 00 <43> c6 44 2f 04 f8 75 70 f7 44 24 50 00 02 00 00 74 01 fb 48 c7 44
RSP: 0018:ffffc900001e0680 EFLAGS: 00000046
RAX: 0000000000000001 RBX: da2e616334457c0f RCX: 477c6d01155d8a00
RDX: 0000000000000007 RSI: ffffffff8a8c23a0 RDI: ffffffff8adf0f60
RBP: ffffc900001e0790 R08: ffffffff8e1fd76f R09: 1ffffffff1c3faed
R10: dffffc0000000000 R11: fffffbfff1c3faee R12: ffff88807c6fc778
R13: dffffc0000000000 R14: ffff88807c6fc650 R15: 1ffff9200003c0dc
FS:  00007f73c95e26c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100000000 CR3: 000000002cfa1000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 rcu_lock_release include/linux/rcupdate.h:355 [inline]
 rcu_read_unlock include/linux/rcupdate.h:824 [inline]
 trace_call_bpf+0x5ca/0x6b0 kernel/trace/bpf_trace.c:137
 perf_trace_run_bpf_submit+0x79/0x1c0 kernel/events/core.c:9997
 perf_trace_preemptirq_template+0x268/0x320 include/trace/events/preemptirq.h:14
 trace_irq_enable_rcuidle+0xd3/0x140 include/trace/events/preemptirq.h:40
 trace_hardirqs_on+0x24/0x40 kernel/trace/trace_preemptirq.c:44
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
RIP: 0010:rcu_read_unlock_special+0x7f/0x510 kernel/rcu/tree_plugin.h:685
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 e2 33 95 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc900001e0ac0 EFLAGS: 00000206
RAX: 477c6d01155d8a00 RBX: 1ffff9200003c160 RCX: 477c6d01155d8a00
RDX: dffffc0000000000 RSI: ffffffff8a8c1220 RDI: ffffffff8adf0f60
RBP: ffffc900001e0bb0 R08: ffffffff90af6257 R09: 1ffffffff215ec4a
R10: dffffc0000000000 R11: fffffbfff215ec4b R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8f3b900 R15: 0000000000000002
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
 rcu_read_unlock include/linux/rcupdate.h:823 [inline]
 ieee80211_iterate_active_interfaces_atomic+0x156/0x170 net/mac80211/util.c:826
 mac80211_hwsim_beacon+0xb7/0x1b0 drivers/net/wireless/mac80211_hwsim.c:2147
 __run_hrtimer kernel/time/hrtimer.c:1747 [inline]
 __hrtimer_run_queues+0x54a/0xd50 kernel/time/hrtimer.c:1811
 hrtimer_run_softirq+0x183/0x2a0 kernel/time/hrtimer.c:1828
 handle_softirqs+0x2a1/0x930 kernel/softirq.c:596
 __do_softirq kernel/softirq.c:630 [inline]
 invoke_softirq kernel/softirq.c:470 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:679
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1118
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: 00 00 00 66 90 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 4e a0 2d f7 48 89 df e8 96 68 2e f7 e8 c1 bc 51 f7 fb bf 01 00 00 00 <e8> 86 cb 21 f7 65 8b 05 47 50 cb 75 85 c0 74 02 5b c3 e8 94 64 c9
RSP: 0018:ffffc9000d87f8b0 EFLAGS: 00000282
RAX: 477c6d01155d8a00 RBX: ffffffff8cb560c0 RCX: 477c6d01155d8a00
RDX: dffffc0000000000 RSI: ffffffff8a8c1220 RDI: 0000000000000001
RBP: ffff8880581268a8 R08: ffffffff90af6257 R09: 1ffffffff215ec4a
R10: dffffc0000000000 R11: fffffbfff215ec4b R12: ffff888054e8d000
R13: dffffc0000000000 R14: ffff8880581268a8 R15: ffffc9000d87f9e0
 spin_unlock_irq include/linux/spinlock.h:401 [inline]
 cgroup_migrate_execute+0x62f/0xf30 kernel/cgroup/cgroup.c:2649
 cgroup_attach_task+0x57a/0x870 kernel/cgroup/cgroup.c:2953
 __cgroup1_procs_write+0x2f5/0x3f0 kernel/cgroup/cgroup-v1.c:522
 cgroup_file_write+0x2c5/0x690 kernel/cgroup/cgroup.c:4100
 kernfs_fop_write_iter+0x3b2/0x520 fs/kernfs/file.c:352
 call_write_iter include/linux/fs.h:2265 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x4b1/0xa30 fs/read_write.c:584
 ksys_write+0x14c/0x250 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f73c879c799
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:00007f73c95e2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f73c8a15fa0 RCX: 00007f73c879c799
RDX: 0000000000000012 RSI: 00002000000001c0 RDI: 000000000000000c
RBP: 00007f73c8832bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f73c8a16038 R14: 00007f73c8a15fa0 R15: 00007ffe8bb58888
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/09 16:42 linux-6.1.y f2ddafa93a25 176bead5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in kernfs_fop_write_iter
2026/01/01 07:32 linux-6.1.y 50cbba13faa2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in kernfs_fop_write_iter
* Struck through repros no longer work on HEAD.