syzbot

INFO: task syz.2.1555:12924 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.2.1555      state:D stack:24888 pid:12924 tgid:12922 ppid:5640   task_flags:0x400040 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x125c/0x6730 kernel/sched/core.c:7234
 __schedule_loop kernel/sched/core.c:7311 [inline]
 schedule+0xdd/0x2c0 kernel/sched/core.c:7326
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383
 __mutex_lock_common kernel/locking/mutex.c:726 [inline]
 __mutex_lock+0xccc/0x1bd0 kernel/locking/mutex.c:821
 nfsd_nl_threads_get_doit+0x1c1/0x820 fs/nfsd/nfsctl.c:1754
 genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
 genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
 netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec net/socket.c:775 [inline]
 __sock_sendmsg net/socket.c:790 [inline]
 ____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2684
 ___sys_sendmsg+0x190/0x1e0 net/socket.c:2738
 __sys_sendmsg+0x160/0x210 net/socket.c:2770
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f02c079de59
RSP: 002b:00007f02c15eb028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f02c0a25fa0 RCX: 00007f02c079de59
RDX: 0000000004000094 RSI: 00002000000000c0 RDI: 0000000000000003
RBP: 00007f02c0833e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f02c0a26038 R14: 00007f02c0a25fa0 R15: 00007fff2b965368
 </TASK>

Showing all locks held in the system:
3 locks held by kworker/1:0/24:
 #0: ffff88801bc07140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
 #1: ffffc900001e7d08 ((fqdir_free_work).work){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
 #2: ffffffff8ebf1878 (rcu_state.barrier_mutex){+.+.}-{4:4}, at: rcu_barrier+0x48/0x6d0 kernel/rcu/tree.c:3857
1 lock held by khungtaskd/31:
 #0: ffffffff8ebe5f00 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffffffff8ebe5f00 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #0: ffffffff8ebe5f00 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
2 locks held by syz-executor/5634:
 #0: ffff88807c6f80d8 (&type->s_umount_key#58){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff88807c6f80d8 (&type->s_umount_key#58){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff88807c6f80d8 (&type->s_umount_key#58){++++}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff88807c6f80d8 (&type->s_umount_key#58){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f260 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by kworker/u10:32/8763:
 #0: ffff88801eb7a940 ((wq_completion)iou_exit){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
 #1: ffffc90002db7d08 ((work_completion)(&ctx->exit_work)){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
4 locks held by kworker/u10:36/8767:
 #0: ffff88801caf6140 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
 #1: ffffc90000ab7d08 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
 #2: ffffffff90a85268 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xb8/0x920 net/core/net_namespace.c:673
 #3: ffffffff8ebf19a8 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock+0x19e/0x3c0 kernel/rcu/tree_exp.h:343
2 locks held by syz.0.1543/12863:
 #0: ffffffff90b4c928 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8f06f260 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_listener_set_doit+0xd5/0x1a80 fs/nfsd/nfsctl.c:1964
2 locks held by syz.2.1555/12924:
 #0: ffffffff90b4c928 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8f06f260 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_threads_get_doit+0x1c1/0x820 fs/nfsd/nfsctl.c:1754
2 locks held by getty/13141:
 #0: ffff888022b540a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
 #1: ffffc900039b32e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x419/0x14e0 drivers/tty/n_tty.c:2211
2 locks held by syz-executor/13178:
 #0: ffff8880133860d8 (&type->s_umount_key#58){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff8880133860d8 (&type->s_umount_key#58){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff8880133860d8 (&type->s_umount_key#58){++++}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff8880133860d8 (&type->s_umount_key#58){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f260 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz-executor/13882:
 #0: ffff88807c4960d8 (&type->s_umount_key#58){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff88807c4960d8 (&type->s_umount_key#58){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff88807c4960d8 (&type->s_umount_key#58){++++}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff88807c4960d8 (&type->s_umount_key#58){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f260 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz.7.1780/14294:
 #0: ffffffff90b4c928 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8f06f260 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_svc_export_set_reqs_doit+0x8a/0x2f0 fs/nfsd/export.c:1057
2 locks held by syz.5.1835/14619:
 #0: ffffffff90b4c928 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8f06f260 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_version_set_doit+0xc4/0x7a0 fs/nfsd/nfsctl.c:1814
1 lock held by syz.3.2003/15564:
 #0: ffffffff90a85268 (pernet_ops_rwsem){++++}-{4:4}, at: copy_net_ns+0x451/0x7c0 net/core/net_namespace.c:575

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

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 05/09/2026
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:122
 nmi_trigger_cpumask_backtrace+0x21c/0x2a0 lib/nmi_backtrace.c:65
 trigger_all_cpu_backtrace include/linux/nmi.h:162 [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:353 [inline]
 watchdog+0xcb1/0x1030 kernel/hung_task.c:561
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 4976 Comm: syslogd Tainted: G     U       L      syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:rcu_read_unlock include/linux/rcupdate.h:869 [inline]
RIP: 0010:class_rcu_destructor include/linux/rcupdate.h:1183 [inline]
RIP: 0010:unwind_next_frame+0x745/0x2090 arch/x86/kernel/unwind_orc.c:495
Code: ff 48 c7 c2 40 c3 cb 8b be 49 03 00 00 48 c7 c7 a0 c3 cb 8b c6 05 49 76 52 0f 01 e8 e5 f9 2c 00 e9 9f f9 ff ff e8 bb c0 35 00 <84> c0 0f 85 63 fc ff ff e8 de 87 fe 09 85 c0 0f 84 56 fc ff ff 80
RSP: 0018:ffffc90002d97558 EFLAGS: 00000286
RAX: 0000000000000001 RBX: ffffc90002d97f08 RCX: ffffffff91d4b201
RDX: 0000000000000000 RSI: ffffffff8c400000 RDI: ffffffff8e469920
RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000007
R10: 0000000000000200 R11: 0000000000018c93 R12: ffffc90002d97618
R13: ffffc90002d975c8 R14: ffffc90002d97f08 R15: ffffc90002d975fc
FS:  00007f3975870c80(0000) GS:ffff888123df5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b34bf2ff8 CR3: 00000000249f6000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 arch_stack_walk+0x94/0xf0 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x8e/0xc0 kernel/stacktrace.c:122
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2705 [inline]
 slab_free mm/slub.c:6405 [inline]
 kfree+0x22b/0x6c0 mm/slub.c:6720
 skb_kfree_head net/core/skbuff.c:1077 [inline]
 skb_free_head+0xb9/0x160 net/core/skbuff.c:1089
 skb_release_data+0x6c5/0x8e0 net/core/skbuff.c:1116
 skb_release_all net/core/skbuff.c:1191 [inline]
 __kfree_skb net/core/skbuff.c:1205 [inline]
 consume_skb net/core/skbuff.c:1439 [inline]
 consume_skb+0xc4/0x110 net/core/skbuff.c:1433
 __unix_dgram_recvmsg+0x754/0xc30 net/unix/af_unix.c:2664
 unix_dgram_recvmsg+0xcd/0x100 net/unix/af_unix.c:2681
 sock_recvmsg_nosec net/socket.c:1126 [inline]
 sock_recvmsg+0x1d5/0x220 net/socket.c:1148
 sock_read_iter+0x2b0/0x3a0 net/socket.c:1217
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x960/0xb40 fs/read_write.c:574
 ksys_read+0x1f8/0x250 fs/read_write.c:716
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f39759c0407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffdc2c11de0 EFLAGS: 00000202 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f3975870c80 RCX: 00007f39759c0407
RDX: 00000000000000ff RSI: 000055ec56552950 RDI: 0000000000000000
RBP: 000055ec56552910 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000055ec5655299d
R13: 0000000000000000 R14: 000055ec56552950 R15: 000055ec48989d98
 </TASK>