syzbot


INFO: task hung in rcu_sync_dtor (2)

Status: premoderation: reported on 2026/02/01 12:32
Reported-by: syzbot+ace00cd3d44c952bd8cc@syzkaller.appspotmail.com
First crash: 1d23h, last: 1d23h
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in rcu_sync_dtor kernel 1 1 163d 163d 0/29 auto-obsoleted due to no activity on 2025/11/21 17:19
android-6-12 INFO: task hung in rcu_sync_dtor 1 2 173d 177d 0/1 auto-obsoleted due to no activity on 2025/11/11 17:26

Sample crash report:
INFO: task syz.0.694:2468 blocked for more than 122 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.694       state:D stack:0     pid:2468  tgid:2468  ppid:291    flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5996 [inline]
 __schedule+0x134f/0x1ea0 kernel/sched/core.c:7843
 __schedule_loop kernel/sched/core.c:7924 [inline]
 schedule+0xc5/0x240 kernel/sched/core.c:7939
 schedule_timeout+0xc7/0x3b0 kernel/time/timer.c:2596
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common kernel/sched/completion.c:116 [inline]
 wait_for_common+0x369/0x650 kernel/sched/completion.c:127
 wait_for_completion+0x1c/0x40 kernel/sched/completion.c:148
 rcu_barrier+0x415/0x540 kernel/rcu/tree.c:4657
 rcu_sync_dtor+0xaf/0x170 kernel/rcu/sync.c:187
 percpu_free_rwsem+0x44/0x90 kernel/locking/percpu-rwsem.c:59
 hci_uart_tty_close+0x210/0x230 drivers/bluetooth/hci_ldisc.c:564
 tty_ldisc_close drivers/tty/tty_ldisc.c:455 [inline]
 tty_ldisc_kill drivers/tty/tty_ldisc.c:613 [inline]
 tty_ldisc_release+0x2ad/0x600 drivers/tty/tty_ldisc.c:781
 tty_release_struct+0x2d/0xe0 drivers/tty/tty_io.c:1690
 tty_release+0xc0a/0x1230 drivers/tty/tty_io.c:1861
 __fput+0x1fe/0xa00 fs/file_table.c:429
 ____fput+0x20/0x30 fs/file_table.c:457
 task_work_run+0x1e5/0x260 kernel/task_work.c:246
 resume_user_mode_work+0x35/0x50 include/linux/resume_user_mode.h:50
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x63/0xb0 kernel/entry/common.c:218
 do_syscall_64+0x63/0xf0 arch/x86/entry/common.c:84
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fb677b9aeb9
RSP: 002b:00007fffe8ddee98 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007fffe8ddef80 RCX: 00007fb677b9aeb9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00000000000219cc R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b2dd20000 R11: 0000000000000246 R12: 00007fffe8ddefc0
R13: 00007fb677e15fac R14: 0000000000021a01 R15: 00007fb677e15fa0
 </TASK>
INFO: task syz.3.696:2473 blocked for more than 124 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.3.696       state:D stack:0     pid:2473  tgid:2473  ppid:988    flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5996 [inline]
 __schedule+0x134f/0x1ea0 kernel/sched/core.c:7843
 __schedule_loop kernel/sched/core.c:7924 [inline]
 schedule+0xc5/0x240 kernel/sched/core.c:7939
 schedule_preempt_disabled+0x14/0x30 kernel/sched/core.c:7996
 __mutex_lock_common kernel/locking/mutex.c:707 [inline]
 __mutex_lock+0x960/0x1bb0 kernel/locking/mutex.c:803
 __mutex_lock_slowpath+0xe/0x20 kernel/locking/mutex.c:1134
 mutex_lock+0x113/0x1d0 kernel/locking/mutex.c:285
 rcu_barrier+0x4d/0x540 kernel/rcu/tree.c:4589
 rcu_sync_dtor+0xaf/0x170 kernel/rcu/sync.c:187
 percpu_free_rwsem+0x44/0x90 kernel/locking/percpu-rwsem.c:59
 hci_uart_tty_close+0x210/0x230 drivers/bluetooth/hci_ldisc.c:564
 tty_ldisc_close drivers/tty/tty_ldisc.c:455 [inline]
 tty_ldisc_kill drivers/tty/tty_ldisc.c:613 [inline]
 tty_ldisc_release+0x2ad/0x600 drivers/tty/tty_ldisc.c:781
 tty_release_struct+0x2d/0xe0 drivers/tty/tty_io.c:1690
 tty_release+0xc0a/0x1230 drivers/tty/tty_io.c:1861
 __fput+0x1fe/0xa00 fs/file_table.c:429
 ____fput+0x20/0x30 fs/file_table.c:457
 task_work_run+0x1e5/0x260 kernel/task_work.c:246
 resume_user_mode_work+0x35/0x50 include/linux/resume_user_mode.h:50
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x63/0xb0 kernel/entry/common.c:218
 do_syscall_64+0x63/0xf0 arch/x86/entry/common.c:84
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fa4dbb9aeb9
RSP: 002b:00007ffde3f81ab8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007ffde3f81ba0 RCX: 00007fa4dbb9aeb9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 0000000000021c85 R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b31720000 R11: 0000000000000246 R12: 00007ffde3f81be0
R13: 00007fa4dbe15fac R14: 0000000000021d2f R15: 00007fa4dbe15fa0
 </TASK>
INFO: task syz.1.698:2477 blocked for more than 125 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.698       state:D stack:0     pid:2477  tgid:2477  ppid:292    flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5996 [inline]
 __schedule+0x134f/0x1ea0 kernel/sched/core.c:7843
 __schedule_loop kernel/sched/core.c:7924 [inline]
 schedule+0xc5/0x240 kernel/sched/core.c:7939
 schedule_preempt_disabled+0x14/0x30 kernel/sched/core.c:7996
 __mutex_lock_common kernel/locking/mutex.c:707 [inline]
 __mutex_lock+0x960/0x1bb0 kernel/locking/mutex.c:803
 __mutex_lock_slowpath+0xe/0x20 kernel/locking/mutex.c:1134
 mutex_lock+0x113/0x1d0 kernel/locking/mutex.c:285
 rcu_barrier+0x4d/0x540 kernel/rcu/tree.c:4589
 kvm_mmu_uninit_tdp_mmu+0x1df/0x210 arch/x86/kvm/mmu/tdp_mmu.c:51
 kvm_mmu_uninit_vm+0x27/0x60 arch/x86/kvm/mmu/mmu.c:6572
 kvm_arch_destroy_vm+0x398/0x420 arch/x86/kvm/x86.c:12961
 kvm_destroy_vm virt/kvm/kvm_main.c:1355 [inline]
 kvm_put_kvm+0xb04/0x12c0 virt/kvm/kvm_main.c:1392
 kvm_vcpu_release+0x58/0x80 virt/kvm/kvm_main.c:4183
 __fput+0x1fe/0xa00 fs/file_table.c:429
 ____fput+0x20/0x30 fs/file_table.c:457
 task_work_run+0x1e5/0x260 kernel/task_work.c:246
 resume_user_mode_work+0x35/0x50 include/linux/resume_user_mode.h:50
 exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
 exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
 syscall_exit_to_user_mode+0x63/0xb0 kernel/entry/common.c:218
 do_syscall_64+0x63/0xf0 arch/x86/entry/common.c:84
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f1df479aeb9
RSP: 002b:00007fffba710bd8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f1df4a17da0 RCX: 00007f1df479aeb9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f1df4a17da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00007f1df4a17cb0 R11: 0000000000000246 R12: 00000000000228cb
R13: 00007f1df4a1609c R14: 000000000002270b R15: 00007f1df4a16090
 </TASK>
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 37 Comm: khungtaskd Not tainted syzkaller #0 001c7e68fa735976e9f6b7ad125989e1d2b10b0e
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x140/0x1c0 lib/dump_stack.c:120
 dump_stack+0x19/0x20 lib/dump_stack.c:129
 nmi_cpu_backtrace+0x2ba/0x2d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x142/0x2c0 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:41
 trigger_all_cpu_backtrace include/linux/nmi.h:158 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:267 [inline]
 watchdog+0xdad/0xf00 kernel/hung_task.c:423
 kthread+0x2c9/0x370 kernel/kthread.c:389
 ret_from_fork+0x67/0xa0 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 33 Comm: rcuop/1 Not tainted syzkaller #0 001c7e68fa735976e9f6b7ad125989e1d2b10b0e
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:fib6_check_expired include/net/ip6_fib.h:280 [inline]
RIP: 0010:__find_rr_leaf+0x182/0x840 net/ipv6/route.c:843
Code: 8f e8 fc eb c9 e8 6e c8 90 fc 4d 8d 7e 64 4c 89 fb 48 c1 eb 03 42 0f b6 04 2b 84 c0 0f 85 38 03 00 00 4c 89 7c 24 18 45 8b 3f <44> 89 fe 81 e6 00 00 40 00 31 ff e8 7e cc 90 fc 44 89 f8 25 00 00
RSP: 0018:ffffc9000022fd00 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 1ffff1102166be8c RCX: ffff888103678000
RDX: 0000000000000100 RSI: 0000000000000100 RDI: 0000000000000100
RBP: ffffc9000022fe58 R08: ffffc9000022ff80 R09: ffffc9000022ff90
R10: ffffc900002300f0 R11: fffff52000046022 R12: 0000000000000100
R13: dffffc0000000000 R14: ffff88810b35f400 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd7ab5de1b8 CR3: 000000010fe4c000 CR4: 00000000003526b0
Call Trace:
 <IRQ>
 find_rr_leaf net/ipv6/route.c:890 [inline]
 rt6_select net/ipv6/route.c:934 [inline]
 fib6_table_lookup+0x2ee/0x9e0 net/ipv6/route.c:2241
 ip6_pol_route+0x17a/0x1360 net/ipv6/route.c:2277
 ip6_pol_route_input+0x5a/0x80 net/ipv6/route.c:2334
 pol_lookup_func include/net/ip6_fib.h:626 [inline]
 fib6_rule_lookup+0x4ee/0x6d0 net/ipv6/fib6_rules.c:117
 ip6_route_input_lookup net/ipv6/route.c:2346 [inline]
 ip6_route_input+0x62e/0x8f0 net/ipv6/route.c:2642
 ip6_rcv_finish_core net/ipv6/ip6_input.c:66 [inline]
 ip6_rcv_finish+0x15a/0x3e0 net/ipv6/ip6_input.c:77
 NF_HOOK include/linux/netfilter.h:317 [inline]
 ipv6_rcv+0xf1/0x240 net/ipv6/ip6_input.c:309
 __netif_receive_skb_one_core net/core/dev.c:5763 [inline]
 __netif_receive_skb net/core/dev.c:5876 [inline]
 netif_receive_skb_internal net/core/dev.c:5962 [inline]
 netif_receive_skb+0x147/0x7b0 net/core/dev.c:6021
 br_netif_receive_skb net/bridge/br_input.c:30 [inline]
 NF_HOOK include/linux/netfilter.h:317 [inline]
 br_pass_frame_up+0x126/0x1b0 net/bridge/br_input.c:70
 br_handle_frame_finish+0x1317/0x1760 net/bridge/br_input.c:221
 nf_hook_bridge_pre net/bridge/br_input.c:301 [inline]
 br_handle_frame+0x5a6/0xba0 net/bridge/br_input.c:424
 __netif_receive_skb_core+0xfae/0x3ab0 net/core/dev.c:5657
 __netif_receive_skb_one_core net/core/dev.c:5761 [inline]
 __netif_receive_skb net/core/dev.c:5876 [inline]
 process_backlog+0x3e5/0xad0 net/core/dev.c:6212
 __napi_poll+0xd3/0x610 net/core/dev.c:6863
 napi_poll net/core/dev.c:6932 [inline]
 net_rx_action+0x5ea/0xd80 net/core/dev.c:7054
 handle_softirqs+0x1aa/0x630 kernel/softirq.c:621
 __do_softirq+0xf/0x16 kernel/softirq.c:659
 do_softirq+0xb8/0x110 kernel/softirq.c:503
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x74/0x80 kernel/softirq.c:430
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 rcu_do_batch+0x5d9/0xd40 kernel/rcu/tree.c:2594
 nocb_cb_wait kernel/rcu/tree_nocb.h:923 [inline]
 rcu_nocb_cb_kthread+0x524/0xb30 kernel/rcu/tree_nocb.h:957
 kthread+0x2c9/0x370 kernel/kthread.c:389
 ret_from_fork+0x67/0xa0 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
net_ratelimit: 143567 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: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 bridge_slave_0 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: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 bridge_slave_0 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 (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/01 12:31 android16-6.12 c13babfee861 6b8752f2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in rcu_sync_dtor
* Struck through repros no longer work on HEAD.