syzbot


INFO: task hung in do_fb_ioctl

Status: upstream: reported on 2025/10/07 02:24
Reported-by: syzbot+2fa94f75fd3eb31750c0@syzkaller.appspotmail.com
First crash: 4d00h, last: 4d00h
Similar bugs (10)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in do_fb_ioctl (4) fbdev 1 1 880d 880d 0/29 auto-obsoleted due to no activity on 2023/07/13 16:33
upstream INFO: task hung in do_fb_ioctl (3) fbdev 1 2 1107d 1132d 0/29 auto-obsoleted due to no activity on 2023/01/02 23:29
upstream BUG: workqueue lockup (5) arm net 1 C done 13608 1h22m 2096d 0/29 upstream: reported C repro on 2020/01/14 22:04
upstream INFO: task hung in do_fb_ioctl (5) fbdev 1 1 387d 387d 0/29 auto-obsoleted due to no activity on 2024/12/17 19:15
upstream INFO: task hung in do_fb_ioctl (2) fbdev 1 1 1327d 1327d 0/29 auto-closed as invalid on 2022/05/22 20:52
linux-6.1 INFO: task hung in do_fb_ioctl 1 1 75d 75d 0/3 upstream: reported on 2025/07/27 03:50
linux-4.19 INFO: task hung in do_fb_ioctl 1 1 2101d 2101d 0/1 auto-closed as invalid on 2020/05/08 18:42
upstream INFO: task hung in do_fb_ioctl fbdev 1 47 1890d 2098d 0/29 closed as dup on 2020/07/27 22:56
linux-4.14 INFO: task hung in do_fb_ioctl 1 C error 24 1780d 2138d 0/1 upstream: reported C repro on 2019/12/03 05:09
linux-4.19 INFO: task hung in do_fb_ioctl (2) 1 C done 7 1510d 1925d 1/1 fixed on 2021/09/21 12:35

Sample crash report:
INFO: task syz.0.5595:18112 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.5595      state:D stack:27912 pid:18112 ppid:5788   flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 schedule+0xbd/0x170 kernel/sched/core.c:6773
 schedule_timeout+0x9b/0x280 kernel/time/timer.c:2143
 ___down_common kernel/locking/semaphore.c:229 [inline]
 __down_common+0x308/0x640 kernel/locking/semaphore.c:250
 down+0x80/0xd0 kernel/locking/semaphore.c:64
 console_lock+0x145/0x1b0 kernel/printk/printk.c:2686
 do_fb_ioctl+0x57e/0x740 drivers/video/fbdev/core/fb_chrdev.c:86
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa7cfb8eec9
RSP: 002b:00007fa7d0a1b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fa7cfde5fa0 RCX: 00007fa7cfb8eec9
RDX: 0000200000000100 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 00007fa7cfc11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa7cfde6038 R14: 00007fa7cfde5fa0 R15: 00007ffcc8baa9f8
 </TASK>

Showing all locks held in the system:
1 lock held by kthreadd/2:
1 lock held by pool_workqueue_/3:
 #0: ffffffff8cd358f8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:292 [inline]
 #0: ffffffff8cd358f8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x448/0x830 kernel/rcu/tree_exp.h:1004
4 locks held by kworker/0:0/8:
 #0: ffff88802d844538 ((wq_completion)wg-kex-wg2#4){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #0: ffff88802d844538 ((wq_completion)wg-kex-wg2#4){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #1: ffffc900000d7d00 ((work_completion)(&({ do { const void *__vpp_verify = (typeof((worker) + 0))((void *)0); (void)__vpp_verify; } while (0); ({ unsigned long __ptr; __ptr = (unsigned long) ((typeof(*((worker))) *)((worker))); (typeof((typeof(*((worker))) *)((worker)))) (__ptr + (((__per_cpu_offset[(cpu)])))); }); })->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #1: ffffc900000d7d00 ((work_completion)(&({ do { const void *__vpp_verify = (typeof((worker) + 0))((void *)0); (void)__vpp_verify; } while (0); ({ unsigned long __ptr; __ptr = (unsigned long) ((typeof(*((worker))) *)((worker))); (typeof((typeof(*((worker))) *)((worker)))) (__ptr + (((__per_cpu_offset[(cpu)])))); }); })->work)){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #2: ffff888076f3d208 (&wg->static_identity.lock){++++}-{3:3}, at: wg_noise_handshake_consume_initiation+0x151/0x900 drivers/net/wireguard/noise.c:598
 #3: ffff888026244df8 (&handshake->lock){++++}-{3:3}, at: wg_noise_handshake_consume_initiation+0x4df/0x900 drivers/net/wireguard/noise.c:632
4 locks held by kworker/u4:1/12:
1 lock held by khungtaskd/29:
 #0: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 #0: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
 #0: ffffffff8cd2ff20 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x290 kernel/locking/lockdep.c:6633
4 locks held by kworker/u4:3/48:
5 locks held by kworker/1:2/786:
2 locks held by kworker/0:2/964:
 #0: ffff888017872538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #0: ffff888017872538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #1: ffffc90004037d00 ((work_completion)(&rew->rew_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #1: ffffc90004037d00 ((work_completion)(&rew->rew_work)){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
4 locks held by kworker/u4:8/2962:
3 locks held by kworker/R-bat_e/3380:
4 locks held by kworker/u4:10/3477:
 #0: ffff88801afc7938 ((wq_completion)wg-kex-wg1){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #0: ffff88801afc7938 ((wq_completion)wg-kex-wg1){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #1: ffffc9000c837d00 ((work_completion)(&peer->transmit_handshake_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #1: ffffc9000c837d00 ((work_completion)(&peer->transmit_handshake_work)){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #2: ffff88802f709208 (&wg->static_identity.lock){++++}-{3:3}, at: wg_noise_handshake_create_initiation+0x10b/0x7e0 drivers/net/wireguard/noise.c:529
 #3: ffff8880262415e8 (&handshake->lock){++++}-{3:3}, at: wg_noise_handshake_create_initiation+0x11c/0x7e0 drivers/net/wireguard/noise.c:530
4 locks held by kworker/u4:11/3500:
2 locks held by klogd/5149:
2 locks held by udevd/5160:
2 locks held by dhcpcd/5454:
2 locks held by dhcpcd/5455:
3 locks held by crond/5534:
2 locks held by getty/5552:
 #0: ffff8880307d20a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc9000326e2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x425/0x1380 drivers/tty/n_tty.c:2217
1 lock held by syz-executor/5778:
1 lock held by syz-executor/5793:
5 locks held by syz-executor/5792:
4 locks held by kworker/1:3/5837:
2 locks held by kworker/1:5/5858:
3 locks held by kworker/0:5/5879:
 #0: ffff88801afc6d38 ((wq_completion)wg-kex-wg1#2){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #0: ffff88801afc6d38 ((wq_completion)wg-kex-wg1#2){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #1: ffffc90004a2fd00 ((work_completion)(&({ do { const void *__vpp_verify = (typeof((worker) + 0))((void *)0); (void)__vpp_verify; } while (0); ({ unsigned long __ptr; __ptr = (unsigned long) ((typeof(*((worker))) *)((worker))); (typeof((typeof(*((worker))) *)((worker)))) (__ptr + (((__per_cpu_offset[(cpu)])))); }); })->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #1: ffffc90004a2fd00 ((work_completion)(&({ do { const void *__vpp_verify = (typeof((worker) + 0))((void *)0); (void)__vpp_verify; } while (0); ({ unsigned long __ptr; __ptr = (unsigned long) ((typeof(*((worker))) *)((worker))); (typeof((typeof(*((worker))) *)((worker)))) (__ptr + (((__per_cpu_offset[(cpu)])))); }); })->work)){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #2: ffff8880262415e8 (&handshake->lock){++++}-{3:3}, at: wg_noise_handshake_begin_session+0x36/0xbd0 drivers/net/wireguard/noise.c:822
2 locks held by kworker/1:6/5884:
4 locks held by kworker/u4:14/8226:
4 locks held by kworker/u4:18/8237:
4 locks held by kworker/u4:20/8243:
4 locks held by kworker/0:3/14665:
2 locks held by syz.1.5592/18106:
4 locks held by kworker/u4:0/18113:
3 locks held by kworker/u4:2/18114:
4 locks held by kworker/u4:4/18115:
 #0: ffff88802d844138 ((wq_completion)wg-kex-wg2#3){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #0: ffff88802d844138 ((wq_completion)wg-kex-wg2#3){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #1: ffffc900044efd00 ((work_completion)(&peer->transmit_handshake_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2609 [inline]
 #1: ffffc900044efd00 ((work_completion)(&peer->transmit_handshake_work)){+.+.}-{0:0}, at: process_scheduled_works+0x957/0x15b0 kernel/workqueue.c:2711
 #2: ffff888076f3d208 (&wg->static_identity.lock){++++}-{3:3}, at: wg_noise_handshake_create_initiation+0x10b/0x7e0 drivers/net/wireguard/noise.c:529
 #3: ffff888026244df8 (&handshake->lock){++++}-{3:3}, at: wg_noise_handshake_create_initiation+0x11c/0x7e0 drivers/net/wireguard/noise.c:530
3 locks held by kworker/u4:5/18116:

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 29 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x39b/0x3d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x2f0 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
 watchdog+0xf41/0xf80 kernel/hung_task.c:379
 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>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 3380 Comm: kworker/R-bat_e Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: bat_events batadv_tt_purge
RIP: 0010:__sanitizer_cov_trace_switch+0x100/0x120 kernel/kcov.c:-1
Code: f3 48 c1 e3 05 4c 8d 63 28 4d 39 fc 77 9d 49 ff c6 4d 89 33 49 89 4c 1b 08 4d 89 54 1b 10 49 89 7c 1b 18 49 89 54 1b 20 eb 81 <5b> 41 5c 41 5e 41 5f c3 b9 05 00 00 00 48 85 c0 0f 85 52 ff ff ff
RSP: 0018:ffffc900001efa30 EFLAGS: 00000246
RAX: 0000000000000002 RBX: ffffffff8ecdeb6e RCX: 0000000000000003
RDX: ffffffff813aa915 RSI: ffffffff8cb9e740 RDI: 0000000000000002
RBP: ffffc900001efb78 R08: ffff88802cb11e00 R09: 0000000000000002
R10: 0000000000000001 R11: 0000000000000100 R12: ffffc900001efb28
R13: dffffc0000000000 R14: 0000000000000002 R15: ffffffff8ecdeb73
FS:  0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6a8ba00000 CR3: 000000002e2c7000 CR4: 00000000003506e0
Call Trace:
 <IRQ>
 unwind_next_frame+0x655/0x2970 arch/x86/kernel/unwind_orc.c:505
 arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:328
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4d0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 slab_alloc mm/slub.c:3503 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3510 [inline]
 kmem_cache_alloc+0x11e/0x2e0 mm/slub.c:3519
 skb_ext_maybe_cow net/core/skbuff.c:6658 [inline]
 skb_ext_add+0x1b3/0x8e0 net/core/skbuff.c:6732
 nf_bridge_unshare net/bridge/br_netfilter_hooks.c:165 [inline]
 br_nf_forward_ip+0xc6/0x1110 net/bridge/br_netfilter_hooks.c:709
 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline]
 nf_hook_slow+0xbd/0x200 net/netfilter/core.c:626
 nf_hook include/linux/netfilter.h:259 [inline]
 NF_HOOK+0x213/0x3d0 include/linux/netfilter.h:302
 __br_forward+0x41f/0x600 net/bridge/br_forward.c:115
 deliver_clone net/bridge/br_forward.c:131 [inline]
 maybe_deliver+0xb5/0x150 net/bridge/br_forward.c:190
 br_flood+0x31b/0x680 net/bridge/br_forward.c:236
 br_handle_frame_finish+0x144f/0x1920 net/bridge/br_input.c:215
 br_nf_hook_thresh+0x3b6/0x480 net/bridge/br_netfilter_hooks.c:1184
 br_nf_pre_routing_finish_ipv6+0x9e3/0xd90 net/bridge/br_netfilter_ipv6.c:-1
 NF_HOOK include/linux/netfilter.h:304 [inline]
 br_nf_pre_routing_ipv6+0x34d/0x680 net/bridge/br_netfilter_ipv6.c:184
 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline]
 nf_hook_bridge_pre net/bridge/br_input.c:277 [inline]
 br_handle_frame+0x96b/0x1480 net/bridge/br_input.c:424
 __netif_receive_skb_core+0xf6b/0x3ac0 net/core/dev.c:5502
 __netif_receive_skb_one_core net/core/dev.c:5606 [inline]
 __netif_receive_skb+0x74/0x290 net/core/dev.c:5722
 process_backlog+0x380/0x6e0 net/core/dev.c:6050
 __napi_poll+0xc0/0x460 net/core/dev.c:6612
 napi_poll net/core/dev.c:6679 [inline]
 net_rx_action+0x5ea/0xbf0 net/core/dev.c:6815
 handle_softirqs+0x280/0x820 kernel/softirq.c:578
 do_softirq+0xed/0x180 kernel/softirq.c:479
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0x178/0x1c0 kernel/softirq.c:406
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 batadv_tt_global_purge net/batman-adv/translation-table.c:2314 [inline]
 batadv_tt_purge+0x4d8/0x9f0 net/batman-adv/translation-table.c:3583
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 rescuer_thread+0x50b/0xbe0 kernel/workqueue.c:2888
 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>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/07 02:23 linux-6.6.y e617101e5626 8ef35d49 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: task hung in do_fb_ioctl
* Struck through repros no longer work on HEAD.