INFO: rcu detected stall in shmem_file_write_iter (2)

Status: upstream: reported on 2026/07/31 20:44
Reported-by: syzbot+07015a52da04d299ded0@syzkaller.appspotmail.com
First crash: 73d, last: 4d19h
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in shmem_file_write_iter (2) mm 1 142 599d 869d 0/29 auto-obsoleted due to no activity on 2025/05/01 06:33
linux-6.6 INFO: rcu detected stall in shmem_file_write_iter 1 7 249d 453d 0/2 auto-obsoleted due to no activity on 2026/05/16 20:03
upstream INFO: rcu detected stall in shmem_file_write_iter (3) prio:low mm 1 syz, C 98 6d20h 355d 0/29 upstream: reported C repro on 2025/10/22 03:00
upstream INFO: rcu detected stall in shmem_file_write_iter mm 1 4 1019d 1062d 0/29 auto-obsoleted due to no activity on 2024/03/27 04:51

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	1-...!: (0 ticks this GP) idle=a614/1/0x4000000000000000 softirq=41622/41622 fqs=0
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5781/1:b..l
rcu: 	(detected by 0, t=10505 jiffies, g=50661, q=256 ncpus=2)
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 11236 Comm: syz.5.1936 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:check_kcov_mode kernel/kcov.c:178 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:241 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp1+0x1f/0x90 kernel/kcov.c:295
Code: 89 74 0a 18 48 89 44 0a 20 c3 90 f3 0f 1e fa 48 8b 04 24 65 48 8b 15 b0 24 7c 7e 65 8b 0d b1 24 7c 7e 81 e1 00 01 ff 00 74 11 <81> f9 00 01 00 00 75 5b 83 ba 24 16 00 00 00 74 52 8b 8a 00 16 00
RSP: 0018:ffffc900001f0d18 EFLAGS: 00000006
RAX: ffffffff8177abc7 RBX: ffff88807ddbd340 RCX: 0000000000010000
RDX: ffff88802edb3c00 RSI: 0000000000000001 RDI: 0000000000000002
RBP: 0000000000000001 R08: ffffffff8f6c5aef R09: 1ffffffff1ed8b5d
R10: dffffc0000000000 R11: fffffbfff1ed8b5e R12: 0000000000000001
R13: dffffc0000000000 R14: ffff8880b8d2b940 R15: 0000000000000000
FS:  00007fed212746c0(0000) GS:ffff8880b8d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc8a6b556c8 CR3: 000000005b595000 CR4: 00000000003506e0
Call Trace:
 <IRQ>
 variable_test_bit arch/x86/include/asm/bitops.h:228 [inline]
 arch_test_bit arch/x86/include/asm/bitops.h:240 [inline]
 _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:142 [inline]
 cpumask_test_cpu include/linux/cpumask.h:504 [inline]
 cpu_online include/linux/cpumask.h:1082 [inline]
 trace_hrtimer_start include/trace/events/timer.h:203 [inline]
 debug_activate kernel/time/hrtimer.c:505 [inline]
 enqueue_hrtimer+0x97/0x380 kernel/time/hrtimer.c:1100
 __run_hrtimer kernel/time/hrtimer.c:1771 [inline]
 __hrtimer_run_queues+0x62f/0xc10 kernel/time/hrtimer.c:1818
 hrtimer_interrupt+0x39d/0x980 kernel/time/hrtimer.c:1880
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1077 [inline]
 __sysvec_apic_timer_interrupt+0xfb/0x3b0 arch/x86/kernel/apic/apic.c:1094
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0x9f/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:lock_is_held_type+0x13e/0x190 kernel/locking/lockdep.c:5866
Code: 75 40 48 c7 04 24 00 00 00 00 9c 8f 04 24 f7 04 24 00 02 00 00 75 46 41 f7 c5 00 02 00 00 74 01 fb 65 48 8b 04 25 28 00 00 00 <48> 3b 44 24 08 75 3c 89 e8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f
RSP: 0018:ffffc9000f267780 EFLAGS: 00000206
RAX: a3ccf7e64bd8ab00 RBX: ffff88802edb3c00 RCX: a3ccf7e64bd8ab00
RDX: ffff88802edb3c00 RSI: ffffffff8acae160 RDI: ffffffff8b1d5160
RBP: 0000000000000000 R08: dffffc0000000000 R09: 1ffffffff23fe2a0
R10: dffffc0000000000 R11: fffffbfff23fe2a1 R12: 0000000000000003
R13: 0000000000000246 R14: ffffffff8df5bd28 R15: ffff88802edb4760
 lock_is_held include/linux/lockdep.h:288 [inline]
 task_css include/linux/cgroup.h:436 [inline]
 blkcg_css+0xa4/0x1c0 block/blk-cgroup.c:111
 blk_cgroup_congested+0xbe/0x220 block/blk-cgroup.c:2207
 __folio_throttle_swaprate+0x71/0x1a0 mm/swapfile.c:3656
 folio_throttle_swaprate include/linux/swap.h:649 [inline]
 shmem_add_to_page_cache+0x9a0/0x1b80 mm/shmem.c:793
 shmem_get_folio_gfp+0x1037/0x2b40 mm/shmem.c:2071
 shmem_get_folio mm/shmem.c:2164 [inline]
 shmem_write_begin+0xf2/0x430 mm/shmem.c:2706
 generic_perform_write+0x2fe/0x5c0 mm/filemap.c:4036
 shmem_file_write_iter+0xfb/0x120 mm/shmem.c:2883
 call_write_iter include/linux/fs.h:2018 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x474/0x9a0 fs/read_write.c:584
 ksys_write+0x151/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fed2035e9ce
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007fed21273da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fed212746c0 RCX: 00007fed2035e9ce
RDX: 0000000000200000 RSI: 00007fed161f7000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007fed21273ee0 R14: 00007fed21273ea0 R15: 00007fed161f7000
 </TASK>
task:syz-executor    state:R  running task     stack:21800 pid:5781  ppid:5772   flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x15ae/0x4660 kernel/sched/core.c:6701
 preempt_schedule_notrace+0xdd/0x110 kernel/sched/core.c:6961
 preempt_schedule_notrace_thunk+0x1a/0x30 arch/x86/entry/thunk_64.S:46
 rcu_is_watching+0x7a/0xb0 kernel/rcu/tree.c:701
 rcu_read_lock_held_common kernel/rcu/update.c:108 [inline]
 rcu_read_lock_held+0x15/0x40 kernel/rcu/update.c:348
 task_css include/linux/cgroup.h:436 [inline]
 mem_cgroup_from_task+0x9a/0x110 mm/memcontrol.c:1038
 get_obj_cgroup_from_current+0x167/0x280 mm/memcontrol.c:3062
 memcg_slab_pre_alloc_hook mm/slab.h:492 [inline]
 slab_pre_alloc_hook+0x8c/0x300 mm/slab.h:719
 slab_alloc_node mm/slub.c:3477 [inline]
 slab_alloc mm/slub.c:3503 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3510 [inline]
 kmem_cache_alloc+0x5a/0x2c0 mm/slub.c:3519
 dup_mm kernel/fork.c:1691 [inline]
 copy_mm+0x178/0x1e30 kernel/fork.c:1749
 copy_process+0x16c9/0x3da0 kernel/fork.c:2510
 kernel_clone+0x24b/0x8a0 kernel/fork.c:2919
 __do_sys_clone kernel/fork.c:3062 [inline]
 __se_sys_clone kernel/fork.c:3046 [inline]
 __x64_sys_clone+0x1b7/0x230 kernel/fork.c:3046
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc8a5dc6c12
RSP: 002b:00007ffc28388ff0 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007ffc28388ff0 RCX: 00007fc8a5dc6c12
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 00007ffc2838917c R08: 0000000000000000 R09: 0000000000000001
R10: 0000555587c927d0 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000000927c0 R14: 000000000004c339 R15: 00007ffc283891d0
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10504 jiffies! g50661 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=1 timer-softirq=25831
rcu: rcu_preempt kthread starved for 10505 jiffies! g50661 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I stack:27848 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x15ae/0x4660 kernel/sched/core.c:6701
 schedule+0xbd/0x170 kernel/sched/core.c:6775
 schedule_timeout+0x188/0x2d0 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x30d/0x1590 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x9d/0x3b0 kernel/rcu/tree.c:1866
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 11236 Comm: syz.5.1936 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:__lock_acquire+0x2a4/0x7eb0 kernel/locking/lockdep.c:5068
Code: ff 49 b8 00 00 00 00 00 fc ff df 48 89 c3 48 85 c0 0f 84 b7 24 00 00 48 8b 44 24 30 4c 8d b0 e0 0a 00 00 4c 89 f0 48 c1 e8 03 <48> 89 44 24 78 42 0f b6 04 00 84 c0 0f 85 5f 17 00 00 45 8b 3e 48
RSP: 0018:ffffc900001f08e0 EFLAGS: 00000802
RAX: 1ffff11005db68dc RBX: ffffffff919d9680 RCX: 000000000000802c
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88807ddbd300
RBP: ffffc900001f0b28 R08: dffffc0000000000 R09: 0000000000000001
R10: dffffc0000000000 R11: fffffbfff1ed8b5e R12: 0000000000000000
R13: ffffffff919d96c0 R14: ffff88802edb46e0 R15: ffffffff984c55c0
FS:  00007fed212746c0(0000) GS:ffff8880b8d00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc8a6b556c8 CR3: 000000005b595000 CR4: 00000000003506e0
Call Trace:
 <IRQ>
 lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5790
 __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
 _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
 spin_lock include/linux/spinlock.h:351 [inline]
 advance_sched+0xbb/0xc70 net/sched/sch_taprio.c:940
 __run_hrtimer kernel/time/hrtimer.c:1754 [inline]
 __hrtimer_run_queues+0x525/0xc10 kernel/time/hrtimer.c:1818
 hrtimer_interrupt+0x39d/0x980 kernel/time/hrtimer.c:1880
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1077 [inline]
 __sysvec_apic_timer_interrupt+0xfb/0x3b0 arch/x86/kernel/apic/apic.c:1094
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0x9f/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:lock_is_held_type+0x13e/0x190 kernel/locking/lockdep.c:5866
Code: 75 40 48 c7 04 24 00 00 00 00 9c 8f 04 24 f7 04 24 00 02 00 00 75 46 41 f7 c5 00 02 00 00 74 01 fb 65 48 8b 04 25 28 00 00 00 <48> 3b 44 24 08 75 3c 89 e8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f
RSP: 0018:ffffc9000f267780 EFLAGS: 00000206
RAX: a3ccf7e64bd8ab00 RBX: ffff88802edb3c00 RCX: a3ccf7e64bd8ab00
RDX: ffff88802edb3c00 RSI: ffffffff8acae160 RDI: ffffffff8b1d5160
RBP: 0000000000000000 R08: dffffc0000000000 R09: 1ffffffff23fe2a0
R10: dffffc0000000000 R11: fffffbfff23fe2a1 R12: 0000000000000003
R13: 0000000000000246 R14: ffffffff8df5bd28 R15: ffff88802edb4760
 lock_is_held include/linux/lockdep.h:288 [inline]
 task_css include/linux/cgroup.h:436 [inline]
 blkcg_css+0xa4/0x1c0 block/blk-cgroup.c:111
 blk_cgroup_congested+0xbe/0x220 block/blk-cgroup.c:2207
 __folio_throttle_swaprate+0x71/0x1a0 mm/swapfile.c:3656
 folio_throttle_swaprate include/linux/swap.h:649 [inline]
 shmem_add_to_page_cache+0x9a0/0x1b80 mm/shmem.c:793
 shmem_get_folio_gfp+0x1037/0x2b40 mm/shmem.c:2071
 shmem_get_folio mm/shmem.c:2164 [inline]
 shmem_write_begin+0xf2/0x430 mm/shmem.c:2706
 generic_perform_write+0x2fe/0x5c0 mm/filemap.c:4036
 shmem_file_write_iter+0xfb/0x120 mm/shmem.c:2883
 call_write_iter include/linux/fs.h:2018 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x474/0x9a0 fs/read_write.c:584
 ksys_write+0x151/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fed2035e9ce
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007fed21273da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fed212746c0 RCX: 00007fed2035e9ce
RDX: 0000000000200000 RSI: 00007fed161f7000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000003
R13: 00007fed21273ee0 R14: 00007fed21273ea0 R15: 00007fed161f7000
 </TASK>

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/08 07:01 linux-6.6.y a91a6aa9253c 4f6a9fcf .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in shmem_file_write_iter
2026/10/05 01:35 linux-6.6.y a91a6aa9253c 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in shmem_file_write_iter
2026/08/08 11:51 linux-6.6.y 6436c12a2ced 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in shmem_file_write_iter
2026/07/31 20:44 linux-6.6.y a1153c0deb44 7664cf44 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: rcu detected stall in shmem_file_write_iter
* Struck through repros no longer work on HEAD.