INFO: rcu detected stall in kswapd (4)

Status: upstream: reported syz repro on 2026/10/05 10:05
Subsystems: fs mm
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+f886305df0acc6fa097a@syzkaller.appspotmail.com
First crash: 162d, last: 4d05h
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ID Workflow Result Correct Bug Created Started Finished Revision
189dcf73 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ✅ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ INFO: rcu detected stall in kswapd (4) 2026/05/25 21:32 2026/05/25 21:32 2026/05/25 22:26 c69befb3
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[syzbot] [fs?] [mm?] INFO: rcu detected stall in kswapd (4) 0 (1) 2026/10/05 10:05
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in kswapd (3) mm 1 syz, C 5 645d 728d 0/29 auto-obsoleted due to no activity on 2025/04/08 02:18
upstream INFO: rcu detected stall in kswapd kernel 1 1 2891d 2891d 0/29 auto-closed as invalid on 2019/05/04 06:35
android-49 INFO: rcu detected stall in kswapd 1 syz, C 10 2538d 2731d 0/3 public: reported C repro on 2019/04/14 08:51
upstream INFO: rcu detected stall in kswapd (2) mm kernfs 1 3 801d 822d 0/29 auto-obsoleted due to no activity on 2024/09/24 04:36

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-0): P5719/1:b..l
rcu: 	(detected by 0, t=10502 jiffies, g=57681, q=371 ncpus=1)
task:syz.2.25        state:R  running task     stack:26616 pid:5719  tgid:5719  ppid:5420   task_flags:0x400040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5533 [inline]
 __schedule+0x17db/0x58f0 kernel/sched/core.c:7284
 preempt_schedule_common+0x7f/0xd0 kernel/sched/core.c:7463
 preempt_schedule_thunk+0x16/0x40 arch/x86/entry/thunk.S:12
 __raw_spin_unlock include/linux/spinlock_api_smp.h:201 [inline]
 _raw_spin_unlock+0x41/0x50 kernel/locking/spinlock.c:213
 spin_unlock include/linux/spinlock.h:401 [inline]
 do_wp_page+0x769/0x4b80 mm/memory.c:4467
 handle_pte_fault mm/memory.c:6582 [inline]
 __handle_mm_fault mm/memory.c:6707 [inline]
 handle_mm_fault+0x15d7/0x3750 mm/memory.c:6876
 do_user_addr_fault+0xa4f/0x1340 arch/x86/mm/fault.c:1343
 handle_page_fault arch/x86/mm/fault.c:1483 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
RIP: 0033:0x7f0879a66723
RSP: 002b:00007ffde218fc10 EFLAGS: 00010246
RAX: 00007f0879e25fa0 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000003 RSI: 00007f0879e26038 RDI: 0000000000000000
RBP: 00007f0879e25fb0 R08: 0000000000000000 R09: 00007f0879e26038
R10: 0000000000000003 R11: 0000000000000000 R12: 00007f0879e25fa0
R13: 0000200000000000 R14: 00007ffde218fc88 R15: 00007f0879e25fa0
 </TASK>
rcu: rcu_preempt kthread starved for 3418 jiffies! g57681 f0x0 RCU_GP_WAIT_FQS(5) ->state=R ->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:R  running task     stack:27496 pid:17    tgid:17    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5533 [inline]
 __schedule+0x17db/0x58f0 kernel/sched/core.c:7284
 preempt_schedule_common+0x7f/0xd0 kernel/sched/core.c:7463
 preempt_schedule_thunk+0x16/0x40 arch/x86/entry/thunk.S:12
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:211 [inline]
 _raw_spin_unlock_irqrestore+0x76/0x80 kernel/locking/spinlock.c:221
 debug_object_free+0x294/0x340 lib/debugobjects.c:1038
 schedule_timeout+0x162/0x2c0 kernel/time/sleep_timeout.c:103
 rcu_gp_fqs_loop+0x30c/0x11f0 kernel/rcu/tree.c:2122
 rcu_gp_kthread+0x9e/0x2b0 kernel/rcu/tree.c:2330
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 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: 0 UID: 0 PID: 80 Comm: kswapd1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:finish_task_switch+0x413/0xc60 kernel/sched/core.c:5384
Code: 04 00 00 41 c7 84 24 20 0e 00 00 00 00 00 00 0f 1f 44 00 00 49 83 c4 48 4c 89 e7 e8 b7 5f 55 0a e8 d2 3b 3a 00 fb 4c 8b 65 c8 <49> 8d bc 24 18 17 00 00 48 89 f8 48 c1 e8 03 42 0f b6 04 30 84 c0
RSP: 0018:ffffc90000e97600 EFLAGS: 00000202
RAX: 0000000000076e43 RBX: ffff88801fc3c8e0 RCX: 8000000000000001
RDX: 0000000000000000 RSI: ffffffff8e419dcf RDI: ffffffff8c6dcd80
RBP: ffffc90000e97650 R08: ffffffff907a877f R09: 1ffffffff20f50ef
R10: dffffc0000000000 R11: fffffbfff20f50f0 R12: ffff8880317aa580
R13: ffff88801fc3c8a8 R14: dffffc0000000000 R15: 1ffff11003f8791c
FS:  0000000000000000(0000) GS:ffff88808c2bc000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f0f31591ac0 CR3: 000000004374b000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5536 [inline]
 __schedule+0x17e3/0x58f0 kernel/sched/core.c:7284
 preempt_schedule_irq+0x4b/0x90 kernel/sched/core.c:7606
 irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:539 [inline]
 irqentry_exit+0x14f/0x910 kernel/entry/common.c:167
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:__might_resched+0x144/0x4c0 kernel/sched/core.c:9229
Code: d0 02 00 00 41 f6 45 00 02 75 21 4d 8d ae 38 0b 00 00 4c 89 e8 48 c1 e8 03 0f b6 04 28 84 c0 0f 85 cd 02 00 00 41 83 7d 00 00 <74> 7e 48 c7 c0 80 3c 7a 90 48 c1 e8 03 0f b6 04 28 84 c0 0f 85 45
RSP: 0018:ffffc90000e97980 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000046
RDX: 0000000000000000 RSI: ffffffff8e6a36ef RDI: ffffffff8c6dcd80
RBP: dffffc0000000000 R08: ffffffff907a877f R09: 1ffffffff20f50ef
R10: dffffc0000000000 R11: fffffbfff20f50f0 R12: ffff8880317aaa44
R13: ffff8880317ab0b8 R14: ffff8880317aa580 R15: 1ffff110062f5548
 kthread_freezable_should_stop+0x23/0x180 kernel/kthread.c:199
 kswapd+0x7af/0x32c0 mm/vmscan.c:7535
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Crashes (7):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/01 09:52 upstream 551c722f4080 38f7f0d1 .config console log report syz / log [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root INFO: rcu detected stall in kswapd
2026/08/26 10:55 upstream 45c13f3f9e3b 6a91adb4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root INFO: rcu detected stall in kswapd
2026/06/17 14:17 upstream 9c87e61e3c57 62cc6db3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce INFO: rcu detected stall in kswapd
2026/06/14 22:09 upstream e21ee273e6fa 1d2f3589 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: rcu detected stall in kswapd
2026/05/15 19:24 upstream 70eda68668d1 9cd3beaa .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root INFO: rcu detected stall in kswapd
2026/04/26 14:21 upstream 897d54018cc9 9c2d0995 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce INFO: rcu detected stall in kswapd
2026/06/19 02:25 net 5c121ee63568 a776b0d0 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce INFO: rcu detected stall in kswapd
* Struck through repros no longer work on HEAD.