syzbot

INFO: task syz.1.8899:1481 blocked for more than 143 seconds.
      Tainted: G     U       L      syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.8899      state:D stack:26872 pid:1481  tgid:1470  ppid:5829   task_flags:0x400140 flags:0x00080002
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_preempt_disabled+0x13/0x30 kernel/sched/core.c:7021
 __mutex_lock_common kernel/locking/mutex.c:692 [inline]
 __mutex_lock+0xc9a/0x1b90 kernel/locking/mutex.c:776
 expkey_flush+0x18/0x90 fs/nfsd/export.c:250
 write_flush.isra.0+0x2af/0x3d0 net/sunrpc/cache.c:1550
 pde_write fs/proc/inode.c:330 [inline]
 proc_reg_write+0x240/0x330 fs/proc/inode.c:342
 do_loop_readv_writev fs/read_write.c:850 [inline]
 do_loop_readv_writev fs/read_write.c:835 [inline]
 vfs_writev+0x5ea/0xe10 fs/read_write.c:1059
 do_writev+0x13e/0x340 fs/read_write.c:1103
 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: 0033:0x7f91f219aeb9
RSP: 002b:00007f91f30a0028 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f91f2416180 RCX: 00007f91f219aeb9
RDX: 000000000000000a RSI: 0000200000000240 RDI: 000000000000000b
RBP: 00007f91f2208c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f91f2416218 R14: 00007f91f2416180 R15: 00007fff63d13838
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
 #0: ffffffff8e5e3120 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8e5e3120 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #0: ffffffff8e5e3120 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
4 locks held by kworker/u10:6/17541:
 #0: ffff88801c29f148 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x11ae/0x1840 kernel/workqueue.c:3232
 #1: ffffc90003e5fc98 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x927/0x1840 kernel/workqueue.c:3233
 #2: ffffffff903dd0b0 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xab/0x830 net/core/net_namespace.c:670
 #3: ffffffff8e5ef8f8 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock+0x27f/0x3c0 kernel/rcu/tree_exp.h:311
2 locks held by kworker/u10:8/20735:
2 locks held by syz.1.8899/1471:
 #0: ffffffff904a2850 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1218
 #1: ffffffff8ea470e8 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_threads_set_doit+0x687/0xbc0 fs/nfsd/nfsctl.c:1596
3 locks held by syz.1.8899/1481:
 #0: ffff88806ae5d5f8 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2aa/0x380 fs/file.c:1255
 #1: ffff8880297d0420 (sb_writers#3){.+.+}-{0:0}, at: do_writev+0x13e/0x340 fs/read_write.c:1103
 #2: ffffffff8ea470e8 (nfsd_mutex){+.+.}-{4:4}, at: expkey_flush+0x18/0x90 fs/nfsd/export.c:250
2 locks held by syz.6.9250/3121:
5 locks held by syz.4.9260/3160:

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd 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
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 nmi_cpu_backtrace.cold+0x12d/0x151 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x1d7/0x230 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:161 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x141/0x190 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
 watchdog+0xcc3/0xfe0 kernel/hung_task.c:515
 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>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 20735 Comm: kworker/u10:8 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: krdsd rds_send_worker
RIP: 0010:__sanitizer_cov_trace_pc+0xb/0x70 kernel/kcov.c:213
Code: 5d 00 be 03 00 00 00 5b e9 32 a5 de 02 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 65 8b 05 a5 85 dd 11 <48> 8b 34 24 65 48 8b 15 81 85 dd 11 a9 00 01 ff 00 74 1b f6 c4 01
RSP: 0018:ffffc90000006e40 EFLAGS: 00000246
RAX: 0000000000000302 RBX: ffff88807c20f640 RCX: ffffffff8949f7cf
RDX: ffff8880260bdb80 RSI: ffffffff8949f7dd RDI: ffff8880260bdb80
RBP: 0000000000000008 R08: 0000000000000004 R09: 0000000000000000
R10: 0000000000000042 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000042 R14: 0000000000000000 R15: 0000000000000042
FS:  0000000000000000(0000) GS:ffff8881245e3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000075f9e000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 skb_network_protocol+0x126/0x6d0 net/core/dev.c:3666
 harmonize_features net/core/dev.c:3738 [inline]
 netif_skb_features+0x3a1/0x1310 net/core/dev.c:3851
 validate_xmit_skb+0x8c/0x1560 net/core/dev.c:4006
 __dev_queue_xmit+0x5f3/0x46f0 net/core/dev.c:4824
 dev_queue_xmit include/linux/netdevice.h:3381 [inline]
 neigh_hh_output include/net/neighbour.h:540 [inline]
 neigh_output include/net/neighbour.h:554 [inline]
 ip_finish_output2+0xf34/0x24b0 net/ipv4/ip_output.c:237
 __ip_finish_output.part.0+0x444/0x6f0 net/ipv4/ip_output.c:315
 __ip_finish_output net/ipv4/ip_output.c:303 [inline]
 ip_finish_output net/ipv4/ip_output.c:325 [inline]
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip_output+0x39b/0xec0 net/ipv4/ip_output.c:438
 dst_output include/net/dst.h:464 [inline]
 ip_local_out net/ipv4/ip_output.c:131 [inline]
 __ip_queue_xmit+0x1b73/0x22b0 net/ipv4/ip_output.c:534
 __tcp_transmit_skb+0x2c62/0x43c0 net/ipv4/tcp_output.c:1631
 __tcp_send_ack.part.0+0x4c5/0x930 net/ipv4/tcp_output.c:4464
 __tcp_send_ack net/ipv4/tcp_output.c:4470 [inline]
 tcp_send_ack+0x84/0xa0 net/ipv4/tcp_output.c:4470
 __tcp_ack_snd_check+0x1fe/0x9f0 net/ipv4/tcp_input.c:5932
 tcp_ack_snd_check net/ipv4/tcp_input.c:5986 [inline]
 tcp_ack_snd_check net/ipv4/tcp_input.c:5980 [inline]
 tcp_rcv_established+0xc26/0x36c0 net/ipv4/tcp_input.c:6477
 tcp_v4_do_rcv+0xc64/0x10a0 net/ipv4/tcp_ipv4.c:1881
 tcp_v4_rcv+0x30fd/0x4d50 net/ipv4/tcp_ipv4.c:2324
 ip_protocol_deliver_rcu+0xba/0x4d0 net/ipv4/ip_input.c:207
 ip_local_deliver_finish+0x3f2/0x6e0 net/ipv4/ip_input.c:241
 NF_HOOK include/linux/netfilter.h:318 [inline]
 NF_HOOK include/linux/netfilter.h:312 [inline]
 ip_local_deliver+0x19a/0x1f0 net/ipv4/ip_input.c:262
 dst_input include/net/dst.h:474 [inline]
 ip_rcv_finish net/ipv4/ip_input.c:453 [inline]
 NF_HOOK include/linux/netfilter.h:318 [inline]
 NF_HOOK include/linux/netfilter.h:312 [inline]
 ip_rcv+0x2d9/0x5d0 net/ipv4/ip_input.c:573
 __netif_receive_skb_one_core+0x197/0x1e0 net/core/dev.c:6152
 __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
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:936 [inline]
 __dev_queue_xmit+0x7f1/0x46f0 net/core/dev.c:4859
 dev_queue_xmit include/linux/netdevice.h:3381 [inline]
 neigh_hh_output include/net/neighbour.h:540 [inline]
 neigh_output include/net/neighbour.h:554 [inline]
 ip_finish_output2+0xf34/0x24b0 net/ipv4/ip_output.c:237
 __ip_finish_output.part.0+0x444/0x6f0 net/ipv4/ip_output.c:315
 __ip_finish_output net/ipv4/ip_output.c:303 [inline]
 ip_finish_output net/ipv4/ip_output.c:325 [inline]
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip_output+0x39b/0xec0 net/ipv4/ip_output.c:438
 dst_output include/net/dst.h:464 [inline]
 ip_local_out net/ipv4/ip_output.c:131 [inline]
 __ip_queue_xmit+0x1b73/0x22b0 net/ipv4/ip_output.c:534
 __tcp_transmit_skb+0x2c62/0x43c0 net/ipv4/tcp_output.c:1631
 tcp_transmit_skb net/ipv4/tcp_output.c:1649 [inline]
 tcp_write_xmit+0x12a2/0x86f0 net/ipv4/tcp_output.c:3002
 __tcp_push_pending_frames+0xaf/0x3b0 net/ipv4/tcp_output.c:3185
 tcp_push_pending_frames include/net/tcp.h:2224 [inline]
 tcp_push_pending_frames include/net/tcp.h:2219 [inline]
 __tcp_sock_set_cork.part.0+0x105/0x140 net/ipv4/tcp.c:3635
 __tcp_sock_set_cork net/ipv4/tcp.c:3630 [inline]
 tcp_sock_set_cork+0x9b/0xc0 net/ipv4/tcp.c:3642
 rds_send_xmit+0x169e/0x2610 net/rds/send.c:421
 rds_send_worker+0x94/0x2e0 net/rds/threads.c:200
 process_one_work+0x9c2/0x1840 kernel/workqueue.c:3257
 process_scheduled_works kernel/workqueue.c:3340 [inline]
 worker_thread+0x5da/0xe40 kernel/workqueue.c:3421
 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>