syzbot


INFO: rcu detected stall in shmem_zero_setup

Status: auto-obsoleted due to no activity on 2026/04/29 07:00
Subsystems: mm
[Documentation on labels]
First crash: 90d, last: 90d

Sample crash report:
bridge0: received packet on veth0_to_bridge with own address as source address (addr:02:c4:9d:f6:9e:3c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P20325/1:b..l
rcu: 	(detected by 0, t=10502 jiffies, g=116297, q=472 ncpus=1)
task:syz.4.2816      state:R  running task     stack:26544 pid:20325 tgid:20313 ppid:16322  task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5260 [inline]
 __schedule+0xfe4/0x5e10 kernel/sched/core.c:6867
 preempt_schedule_irq+0x50/0x90 kernel/sched/core.c:7194
 irqentry_exit+0x17b/0x670 kernel/entry/common.c:216
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:lock_acquire+0x5e/0x330 kernel/locking/lockdep.c:5872
Code: 05 bb 49 01 12 83 f8 07 0f 87 a4 02 00 00 48 0f a3 05 46 eb d4 0e 0f 82 6f 02 00 00 8b 35 be 1b d5 0e 85 f6 0f 85 8a 00 00 00 <48> 8b 44 24 30 65 48 2b 05 5d 49 01 12 0f 85 b8 02 00 00 48 83 c4
RSP: 0018:ffffc9000bd07100 EFLAGS: 00000206
RAX: 0000000000000046 RBX: 0000000000000000 RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffffffff8dc1b439 RDI: ffffffff8bfa32a0
RBP: ffffffff8e5e3120 R08: 00000000a986c79a R09: 0000000000000007
R10: 0000000000000200 R11: 0000000000000000 R12: 0000000000000002
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 rcu_read_lock include/linux/rcupdate.h:867 [inline]
 class_rcu_constructor include/linux/rcupdate.h:1195 [inline]
 unwind_next_frame+0xd1/0x1ea0 arch/x86/kernel/unwind_orc.c:495
 arch_stack_walk+0x94/0xf0 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x8e/0xc0 kernel/stacktrace.c:122
 save_stack+0x162/0x1e0 mm/page_owner.c:165
 __reset_page_owner+0x84/0x190 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+0x822/0x1130 mm/page_alloc.c:2973
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x47/0xe0 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4953 [inline]
 slab_alloc_node mm/slub.c:5263 [inline]
 kmem_cache_alloc_lru_noprof+0x2c7/0x7d0 mm/slub.c:5282
 shmem_alloc_inode+0x25/0x50 mm/shmem.c:5152
 alloc_inode+0x68/0x250 fs/inode.c:346
 new_inode+0x22/0x1c0 fs/inode.c:1175
 __shmem_get_inode mm/shmem.c:3068 [inline]
 shmem_get_inode+0x197/0xf30 mm/shmem.c:3142
 __shmem_file_setup+0x279/0x330 mm/shmem.c:5835
 shmem_kernel_file_setup mm/shmem.c:5865 [inline]
 __shmem_zero_setup mm/shmem.c:5905 [inline]
 shmem_zero_setup+0x93/0x1b0 mm/shmem.c:5915
 __mmap_new_vma mm/vma.c:2527 [inline]
 __mmap_region+0x2101/0x2820 mm/vma.c:2752
 mmap_region+0x180/0x3e0 mm/vma.c:2830
 do_mmap+0xc63/0x12f0 mm/mmap.c:558
 vm_mmap_pgoff+0x29e/0x470 mm/util.c:581
 ksys_mmap_pgoff+0x7d/0x5b0 mm/mmap.c:604
 __do_sys_mmap arch/x86/kernel/sys_x86_64.c:89 [inline]
 __se_sys_mmap arch/x86/kernel/sys_x86_64.c:82 [inline]
 __x64_sys_mmap+0x125/0x190 arch/x86/kernel/sys_x86_64.c:82
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f865099aeb9
RSP: 002b:00007f8651829028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f8650c16180 RCX: 00007f865099aeb9
RDX: 00000000000000df RSI: 0000000004020009 RDI: 0000000000000000
RBP: 00007f8650a08c1f R08: 0000000000000401 R09: 0000000000008000
R10: 0000000000000eb1 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8650c16218 R14: 00007f8650c16180 R15: 00007ffc9d7519c8
 </TASK>
rcu: rcu_preempt kthread starved for 345 jiffies! g116297 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->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:28088 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5260 [inline]
 __schedule+0xfe4/0x5e10 kernel/sched/core.c:6867
 __schedule_loop kernel/sched/core.c:6949 [inline]
 schedule+0xdd/0x390 kernel/sched/core.c:6964
 schedule_timeout+0x127/0x280 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x1a9/0xb00 kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x21e/0x320 kernel/rcu/tree.c:2285
 kthread+0x3b3/0x730 kernel/kthread.c:463
 ret_from_fork+0x754/0xaf0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 UID: 0 PID: 3409 Comm: kworker/R-bat_e Tainted: G     U       L      syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026
Workqueue: bat_events batadv_tt_purge
RIP: 0010:in_softirq_really kernel/kcov.c:171 [inline]
RIP: 0010:check_kcov_mode kernel/kcov.c:183 [inline]
RIP: 0010:write_comp_data+0x24/0x90 kernel/kcov.c:246
Code: 90 90 90 90 90 90 65 8b 05 b9 8c dd 11 49 89 f8 49 89 f1 49 89 d2 65 48 8b 3d 90 8c dd 11 a9 00 01 ff 00 74 1b f6 c4 01 74 07 <a9> 00 00 ff 00 74 05 e9 80 dc 70 09 8b 87 6c 16 00 00 85 c0 74 f1
RSP: 0018:ffffc90000007338 EFLAGS: 00000202
RAX: 0000000080000101 RBX: ffff88807a691000 RCX: ffffffff8a4556cd
RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffff888032579e80
RBP: ffff8880a6f5edc0 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000001
R13: ffff88807a691030 R14: ffff88807a691800 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881245e3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055555f8cca28 CR3: 000000002ac4e000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 nbp_vlan_group_rcu net/bridge/br_private.h:1646 [inline]
 should_deliver+0x4d/0x3d0 net/bridge/br_forward.c:26
 maybe_deliver+0x5a/0x180 net/bridge/br_forward.c:183
 br_flood+0x193/0x650 net/bridge/br_forward.c:238
 br_handle_frame_finish+0xf57/0x1f00 net/bridge/br_input.c:229
 br_nf_hook_thresh+0x30d/0x420 net/bridge/br_netfilter_hooks.c:1167
 br_nf_pre_routing_finish_ipv6+0x769/0xfb0 net/bridge/br_netfilter_ipv6.c:154
 NF_HOOK include/linux/netfilter.h:318 [inline]
 br_nf_pre_routing_ipv6+0x39c/0x8b0 net/bridge/br_netfilter_ipv6.c:184
 br_nf_pre_routing+0x93b/0x1510 net/bridge/br_netfilter_hooks.c:508
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_bridge_pre net/bridge/br_input.c:291 [inline]
 br_handle_frame+0xa68/0x1510 net/bridge/br_input.c:442
 __netif_receive_skb_core.constprop.0+0x6d7/0x3460 net/core/dev.c:6039
 __netif_receive_skb_one_core+0xb0/0x1e0 net/core/dev.c:6150
 __netif_receive_skb+0x1f/0x120 net/core/dev.c:6265
 process_backlog+0x37a/0x1580 net/core/dev.c:6617
 __napi_poll.constprop.0+0xaf/0x450 net/core/dev.c:7681
 napi_poll net/core/dev.c:7744 [inline]
 net_rx_action+0xa40/0xf20 net/core/dev.c:7896
 handle_softirqs+0x1ea/0x910 kernel/softirq.c:622
 do_softirq kernel/softirq.c:523 [inline]
 do_softirq+0xac/0xe0 kernel/softirq.c:510
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0xf8/0x120 kernel/softirq.c:450
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 batadv_tt_local_purge+0x21c/0x3d0 net/batman-adv/translation-table.c:1315
 batadv_tt_purge+0x8b/0xbd0 net/batman-adv/translation-table.c:3509
 process_one_work+0x9c2/0x1840 kernel/workqueue.c:3257
 process_scheduled_works kernel/workqueue.c:3340 [inline]
 rescuer_thread+0x8f1/0xf40 kernel/workqueue.c:3528
 kthread+0x3b3/0x730 kernel/kthread.c:463
 ret_from_fork+0x754/0xaf0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
net_ratelimit: 8001 callbacks suppressed
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:02:c4:9d:f6:9e:3c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, 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:02:c4:9d:f6:9e:3c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, 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:02:c4:9d:f6:9e:3c, vlan:0)
net_ratelimit: 9399 callbacks suppressed
bridge0: received packet on veth0_to_bridge with own address as source address (addr:02:c4:9d:f6:9e:3c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, 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:02:c4:9d:f6:9e:3c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, 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:02:c4:9d:f6:9e:3c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/29 07:00 upstream 8dfce8991b95 0adc945e .config console log report info [disk image] [vmlinux] [kernel image] ci-qemu-gce-upstream-auto INFO: rcu detected stall in shmem_zero_setup
* Struck through repros no longer work on HEAD.