INFO: rcu detected stall in filemap_fault (4)

Status: upstream: reported C repro on 2026/07/11 16:44
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+196d7dfb853fc17cf2e2@syzkaller.appspotmail.com
First crash: 89d, last: 53d
Fix bisection: failed (error log)
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/09/24 linux-5.15.y (ToT) 0248c33e835e C [report] INFO: rcu detected stall in sys_mlock
2026/09/24 upstream (ToT) 62f4c998b297 C Didn't crash
▶ ▼ Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 INFO: rcu detected stall in filemap_fault 1 1 186d 186d 0/2 auto-obsoleted due to no activity on 2026/07/14 16:51
upstream INFO: rcu detected stall in filemap_fault (3) mm 1 13 553d 833d 0/29 auto-obsoleted due to no activity on 2025/07/02 21:11
upstream INFO: rcu detected stall in filemap_fault mm 1 1 2923d 2921d 0/29 closed as dup on 2019/01/02 16:20
upstream INFO: rcu detected stall in filemap_fault (2) fs mm 1 7 1794d 1814d 0/29 auto-closed as invalid on 2022/02/07 21:39
linux-5.15 INFO: rcu detected stall in filemap_fault (3) 1 1 380d 380d 0/3 auto-obsoleted due to no activity on 2026/01/01 14:26
linux-6.1 INFO: rcu detected stall in filemap_fault (2) 1 1 21d 21d 0/3 upstream: reported on 2026/09/17 20:37
linux-5.15 INFO: rcu detected stall in filemap_fault (2) 1 4 484d 588d 0/3 auto-obsoleted due to no activity on 2025/09/19 16:02
linux-6.1 INFO: rcu detected stall in filemap_fault 1 2 753d 762d 0/3 auto-obsoleted due to no activity on 2024/12/24 06:37
linux-5.15 INFO: rcu detected stall in filemap_fault 1 2 775d 778d 0/3 auto-obsoleted due to no activity on 2024/12/02 14:29
▶ ▼ Last patch testing requests (2)
Created Duration User Patch Repo Result
2026/09/20 08:30 18m retest repro linux-5.15.y report job log log
2026/09/20 08:30 17m retest repro linux-5.15.y report job log log
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2026/09/21 00:10 0m bisect fix linux-5.15.y error
2026/08/16 15:49 2h16m bisect fix linux-5.15.y OK (0) job log log

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P3559/1:b..l
	(detected by 1, t=10502 jiffies, g=6081, q=37)
task:udevd           state:R  running task     stack:25456 pid: 3559 ppid:     1 flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 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
 spin_unlock_irqrestore include/linux/spinlock.h:419 [inline]
 __wake_up_common_lock kernel/sched/wait.c:140 [inline]
 __wake_up_sync_key+0x128/0x190 kernel/sched/wait.c:205
 sock_def_readable+0x136/0x250 net/core/sock.c:3101
 __netlink_sendskb net/netlink/af_netlink.c:1264 [inline]
 netlink_sendskb+0x97/0x130 net/netlink/af_netlink.c:1270
 netlink_sendmsg+0x8ba/0xbe0 net/netlink/af_netlink.c:1923
 sock_sendmsg_nosec net/socket.c:706 [inline]
 __sock_sendmsg net/socket.c:718 [inline]
 ____sys_sendmsg+0x5be/0x8f0 net/socket.c:2446
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2500
 __sys_sendmsg net/socket.c:2529 [inline]
 __do_sys_sendmsg net/socket.c:2538 [inline]
 __se_sys_sendmsg+0x1b7/0x2a0 net/socket.c:2536
 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: 0033:0x7fad9cc54407
RSP: 002b:00007fff27a565e0 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fad9cb66880 RCX: 00007fad9cc54407
RDX: 0000000000000000 RSI: 00007fff27a56640 RDI: 0000000000000004
RBP: 000055fbc8554510 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000000000a5
R13: 000055fbc85549e0 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 10542 jiffies! g6081 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:27440 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 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/0x11f0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
 kthread+0x42e/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: 4209 Comm: syz-executor271 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <IRQ>
 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+0x845/0x1120 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:2021
 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+0x4b0/0xb60 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x397/0x8b0 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:on_stack arch/x86/include/asm/stacktrace.h:58 [inline]
RIP: 0010:stack_access_ok arch/x86/kernel/unwind_orc.c:347 [inline]
RIP: 0010:deref_stack_reg arch/x86/kernel/unwind_orc.c:357 [inline]
RIP: 0010:unwind_next_frame+0x8f3/0x1cf0 arch/x86/kernel/unwind_orc.c:539
Code: 00 fc ff df 80 3c 08 00 74 05 e8 08 fa 88 00 48 8b 04 24 4c 8d 78 f8 4c 8b 73 10 48 b8 00 00 00 00 00 fc ff df 48 8b 4c 24 30 <0f> b6 04 01 84 c0 0f 85 3d 0f 00 00 83 3b 00 0f 95 c0 4c 39 fd 0f
RSP: 0018:ffffc90002eeecb0 EFLAGS: 00000246
RAX: dffffc0000000000 RBX: ffffc90002eeed48 RCX: 1ffff920005ddda9
RDX: ffffc90002eef818 RSI: ffffffff8da212a0 RDI: ffffc90002eeed58
RBP: ffffc90002ee8000 R08: 000000000000000f R09: 0000000000000009
R10: dffffc0000000000 R11: fffff520005dddb5 R12: 1ffffffff1c24292
R13: 1ffffffff1c24292 R14: ffffc90002ef0000 R15: ffffc90002eef810
 arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kmem_cache_free+0x8f/0x210 mm/slub.c:3520
 submit_bio_checks+0x2f1/0x1990 block/blk-core.c:899
 __submit_bio+0x549/0x780 block/blk-core.c:911
 __submit_bio_noacct_mq block/blk-core.c:997 [inline]
 submit_bio_noacct+0x6b1/0x800 block/blk-core.c:1027
 submit_bio+0x2c6/0x550 block/blk-core.c:1089
 mpage_bio_submit fs/mpage.c:66 [inline]
 mpage_readpage+0x15a/0x210 fs/mpage.c:410
 filemap_read_page+0x18d/0x4b0 mm/filemap.c:2386
 filemap_fault+0xcd3/0x13a0 mm/filemap.c:3174
 __do_fault+0x141/0x330 mm/memory.c:3928
 do_read_fault mm/memory.c:4264 [inline]
 do_fault mm/memory.c:4392 [inline]
 handle_pte_fault mm/memory.c:4650 [inline]
 __handle_mm_fault mm/memory.c:4785 [inline]
 handle_mm_fault+0x2982/0x4440 mm/memory.c:4883
 faultin_page mm/gup.c:976 [inline]
 __get_user_pages+0x952/0x11e0 mm/gup.c:1197
 populate_vma_page_range+0x213/0x290 mm/gup.c:1529
 __mm_populate+0x275/0x3b0 mm/gup.c:1638
 do_mlock+0x49c/0x550 mm/mlock.c:688
 __do_sys_mlock mm/mlock.c:696 [inline]
 __se_sys_mlock mm/mlock.c:694 [inline]
 __x64_sys_mlock+0x5c/0x70 mm/mlock.c:694
 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: 0033:0x7efcb9a48d99
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffee54f8a78 EFLAGS: 00000246 ORIG_RAX: 0000000000000095
RAX: ffffffffffffffda RBX: 0000200000000000 RCX: 00007efcb9a48d99
RDX: 00007efcb9a48d99 RSI: 0000000000800000 RDI: 0000200000000000
RBP: 00000000000f4240 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000021000
R13: 00007ffee54f8ac0 R14: 00007ffee54f8aac R15: 00007efcb9aa804b
 </TASK>

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/13 02:34 linux-5.15.y c86c4726e7f0 d78ea535 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-5-15-kasan INFO: rcu detected stall in filemap_fault
2026/07/12 19:29 linux-5.15.y c86c4726e7f0 d78ea535 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-5-15-kasan INFO: rcu detected stall in filemap_fault
2026/07/11 23:49 linux-5.15.y c86c4726e7f0 d78ea535 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-5-15-kasan INFO: rcu detected stall in filemap_fault
2026/07/11 16:43 linux-5.15.y c86c4726e7f0 d78ea535 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: rcu detected stall in filemap_fault
* Struck through repros no longer work on HEAD.