syzbot


INFO: rcu detected stall in loop_control_ioctl (2)

Status: auto-obsoleted due to no activity on 2026/07/11 07:14
Subsystems: mm
Labels: prio:normal
[Documentation on labels]
First crash: 147d, last: 98d
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
91870ada-f250-470a-afef-90c17f506426 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ INFO: rcu detected stall in loop_control_ioctl (2) 2026/05/30 05:28 2026/05/30 05:28 2026/05/30 06:14 6b4a844333e83556da95d61d7f207e7ef5cd4bc6

			
		
97edd6f9-9670-4d36-8d7c-5a52a5545730 assessment-security 💥 INFO: rcu detected stall in loop_control_ioctl (2) 2026/05/14 08:06 2026/05/14 08:06 2026/05/14 08:07 6ccb967e465e832a7bfd7a116ad00d52a0923a5d
failed to run ["git" "pull" "origin" "HEAD" "--depth=1" "--allow-unrelated-histories"]: exit status 128
From /app/workdir/repo/linux
 * branch                HEAD       -> FETCH_HEAD
Updating files:  ...
truncated to first 200 bytes; open job for full error
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in loop_control_ioctl kernfs 1 1 1071d 1071d 0/29 auto-obsoleted due to no activity on 2023/11/11 10:36
android-5-15 BUG: soft lockup in loop_control_ioctl 1 3 762d 766d 0/2 auto-obsoleted due to no activity on 2024/09/14 23:18
upstream BUG: sleeping function called from invalid context in blk_release_queue 5 C inconclusive 25247 1563d 1580d 0/29 closed as dup on 2022/04/02 11:06

Sample crash report:
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P9274/1:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=45217, q=527 ncpus=2)
task:syz.1.969       state:R  running task     stack:25704 pid:9274  tgid:9272  ppid:5845   task_flags:0x480140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5298 [inline]
 __schedule+0x15dd/0x52d0 kernel/sched/core.c:6911
 preempt_schedule_irq+0x4d/0xa0 kernel/sched/core.c:7238
 irqentry_exit+0x599/0x620 kernel/entry/common.c:239
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:rcu_is_watching+0x70/0xb0 kernel/rcu/tree.c:754
Code: c3 98 f9 1d 93 49 03 1e 48 89 d8 48 c1 e8 03 42 0f b6 04 38 84 c0 75 34 8b 03 65 ff 0d 49 f3 71 11 74 11 83 e0 04 c1 e8 02 5b <41> 5e 41 5f c3 cc cc cc cc cc e8 31 f1 88 ff eb e8 48 c7 c7 00 4b
RSP: 0018:ffffc9001b3d7560 EFLAGS: 00000202
RAX: 0000000000000001 RBX: ffffffff90dacd01 RCX: 0000000080000001
RDX: ffffc9001b3d7601 RSI: ffffffff8c27d560 RDI: ffffffff8c27d520
RBP: dffffc0000000000 R08: ffffc9001b3d7da8 R09: 0000000000000000
R10: ffffc9001b3d7698 R11: fffff5200367aed5 R12: ffffc9001b3d7db8
R13: ffffc9001b3d0000 R14: ffffffff8e1b4790 R15: dffffc0000000000
 rcu_read_unlock include/linux/rcupdate.h:879 [inline]
 class_rcu_destructor include/linux/rcupdate.h:1193 [inline]
 unwind_next_frame+0x1a66/0x23c0 arch/x86/kernel/unwind_orc.c:695
 arch_stack_walk+0x11b/0x150 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xa9/0x100 kernel/stacktrace.c:122
 save_stack+0x122/0x230 mm/page_owner.c:165
 __reset_page_owner+0x71/0x1f0 mm/page_owner.c:320
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 __slab_free+0x263/0x2b0 mm/slub.c:5573
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4538 [inline]
 slab_alloc_node mm/slub.c:4866 [inline]
 __kmalloc_cache_noprof+0x2ba/0x660 mm/slub.c:5375
 kmalloc_noprof include/linux/slab.h:950 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 kobject_uevent_env+0x28c/0x9e0 lib/kobject_uevent.c:543
 device_del+0x750/0x8f0 drivers/base/core.c:3897
 __del_gendisk+0x6e8/0x980 block/genhd.c:753
 del_gendisk+0xe7/0x160 block/genhd.c:823
 loop_remove+0x42/0xc0 drivers/block/loop.c:2120
 loop_control_remove drivers/block/loop.c:2179 [inline]
 loop_control_ioctl+0x4b8/0x5a0 drivers/block/loop.c:2221
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9e6b59c819
RSP: 002b:00007f9e697f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f9e6b816090 RCX: 00007f9e6b59c819
RDX: 0000000000000000 RSI: 0000000000004c81 RDI: 0000000000000009
RBP: 00007f9e6b632c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9e6b816128 R14: 00007f9e6b816090 R15: 00007f9e6b93fa48
 </TASK>
rcu: rcu_preempt kthread starved for 2459 jiffies! g45217 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:27648 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5298 [inline]
 __schedule+0x15dd/0x52d0 kernel/sched/core.c:6911
 __schedule_loop kernel/sched/core.c:6993 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7008
 schedule_timeout+0x158/0x2c0 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x312/0x11d0 kernel/rcu/tree.c:2095
 rcu_gp_kthread+0x9e/0x2b0 kernel/rcu/tree.c:2297
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 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: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:skb_release_data+0x1/0x8f0 net/core/skbuff.c:1103
Code: ff 4c 89 f7 e8 90 ea b9 f8 e9 f6 fe ff ff 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 55 <41> 57 41 56 41 55 41 54 53 48 83 ec 50 89 74 24 34 49 89 fd 49 be
RSP: 0018:ffffc90000a07678 EFLAGS: 00000246
RAX: ffffffff8975faf0 RBX: ffff8881564283c0 RCX: ffff88801de88000
RDX: 0000000000000100 RSI: 0000000000000002 RDI: ffff8881564283c0
RBP: 1ffff1102ac85086 R08: ffffffff9011dbb7 R09: 1ffffffff2023b76
R10: dffffc0000000000 R11: fffffbfff2023b77 R12: 1ffff1102ac85093
R13: ffff8881564283c0 R14: ffff888156428490 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125554000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000103030 CR3: 000000007faa2000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 skb_release_all net/core/skbuff.c:1200 [inline]
 __kfree_skb+0x5d/0x210 net/core/skbuff.c:1214
 packet_rcv+0x175/0x1730 net/packet/af_packet.c:2223
 dev_queue_xmit_nit+0xa39/0xad0 net/core/dev.c:2606
 xmit_one net/core/dev.c:3884 [inline]
 dev_hard_start_xmit+0x1cf/0x870 net/core/dev.c:3904
 __dev_queue_xmit+0x16d1/0x3890 net/core/dev.c:4854
 dev_queue_xmit include/linux/netdevice.h:3385 [inline]
 br_dev_queue_push_xmit+0x370/0x4a0 net/bridge/br_forward.c:53
 NF_HOOK+0x64e/0x6e0 include/linux/netfilter.h:318
 br_nf_post_routing+0xb66/0xfe0 net/bridge/br_netfilter_hooks.c:966
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:623
 nf_hook include/linux/netfilter.h:273 [inline]
 NF_HOOK+0x23e/0x3f0 include/linux/netfilter.h:316
 br_forward_finish+0xd3/0x130 net/bridge/br_forward.c:66
 br_nf_hook_thresh net/bridge/br_netfilter_hooks.c:1167 [inline]
 br_nf_forward_finish+0xa5e/0xe90 net/bridge/br_netfilter_hooks.c:662
 NF_HOOK+0x64e/0x6e0 include/linux/netfilter.h:318
 br_nf_forward_ip+0x7ef/0xa30 net/bridge/br_netfilter_hooks.c:716
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:623
 nf_hook include/linux/netfilter.h:273 [inline]
 NF_HOOK+0x23e/0x3f0 include/linux/netfilter.h:316
 __br_forward+0x397/0x540 net/bridge/br_forward.c:115
 br_handle_frame_finish+0x14c2/0x1bb0 net/bridge/br_input.c:229
 br_nf_hook_thresh+0x3dd/0x4c0 net/bridge/br_netfilter_hooks.c:-1
 br_nf_pre_routing_finish_ipv6+0xa3a/0xd70 net/bridge/br_netfilter_ipv6.c:-1
 NF_HOOK include/linux/netfilter.h:318 [inline]
 br_nf_pre_routing_ipv6+0x374/0x6f0 net/bridge/br_netfilter_ipv6.c:184
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_bridge_pre net/bridge/br_input.c:291 [inline]
 br_handle_frame+0x1277/0x1510 net/bridge/br_input.c:442
 __netif_receive_skb_core+0x98f/0x31a0 net/core/dev.c:6068
 __netif_receive_skb_one_core net/core/dev.c:6179 [inline]
 __netif_receive_skb net/core/dev.c:6294 [inline]
 process_backlog+0x76d/0x1950 net/core/dev.c:6645
 __napi_poll+0xae/0x340 net/core/dev.c:7709
 napi_poll net/core/dev.c:7772 [inline]
 net_rx_action+0x627/0xf70 net/core/dev.c:7929
 handle_softirqs+0x22a/0x870 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x5f/0x150 kernel/softirq.c:723
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1056
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:63
Code: 7e 6b 02 c3 cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d e3 92 19 00 fb f4 <e9> fc e9 02 00 cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90
RSP: 0018:ffffc90000197e20 EFLAGS: 00000246
RAX: 0000000000f5f403 RBX: ffffffff819a9c3a RCX: 0000000080000001
RDX: 0000000000000001 RSI: ffffffff8defbe6a RDI: ffffffff8c27d580
RBP: ffffc90000197f10 R08: ffff8880b873399b R09: 1ffff110170e6733
R10: dffffc0000000000 R11: ffffed10170e6734 R12: 0000000000000001
R13: 1ffff11003bd1000 R14: 0000000000000001 R15: 1ffff11003bd1000
 arch_safe_halt arch/x86/kernel/process.c:766 [inline]
 default_idle+0x9/0x20 arch/x86/kernel/process.c:767
 default_idle_call+0x72/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:199 [inline]
 do_idle+0x36a/0x5f0 kernel/sched/idle.c:352
 cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:451
 start_secondary+0x101/0x110 arch/x86/kernel/smpboot.c:312
 common_startup_64+0x13e/0x147
 </TASK>
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/12 07:07 upstream e753c16cb3dd 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce INFO: rcu detected stall in loop_control_ioctl
2026/02/22 16:28 upstream 32a92f8c8932 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce INFO: rcu detected stall in loop_control_ioctl
* Struck through repros no longer work on HEAD.