Re: [syzbot] [nfs?] INFO: task hung in nfsd_nl_rpc_status_get_start

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2024-06-13 at 12:38 -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    2ccbdf43d5e7 Merge tag 'for-linus' of
> git://git.kernel.org..
> git tree:       upstream
> console output:
> https://syzkaller.appspot.com/x/log.txt?x=158e5256980000
> kernel config: 
> https://syzkaller.appspot.com/x/.config?x=c79815c08cc14227
> dashboard link:
> https://syzkaller.appspot.com/bug?extid=e9820daec56bcb4c41b5
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for
> Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image:
> https://storage.googleapis.com/syzbot-assets/9fb20954c51e/disk-2ccbdf43.raw.xz
> vmlinux:
> https://storage.googleapis.com/syzbot-assets/06d78b3cf960/vmlinux-2ccbdf43.xz
> kernel image:
> https://storage.googleapis.com/syzbot-assets/15e5b0a8df77/bzImage-2ccbdf43.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the
> commit:
> Reported-by: syzbot+e9820daec56bcb4c41b5@syzkaller.appspotmail.com
> 
> INFO: task syz-executor.1:7517 blocked for more than 143 seconds.
>       Not tainted 6.10.0-rc3-syzkaller-00044-g2ccbdf43d5e7 #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
> message.
> task:syz-executor.1  state:D stack:23800 pid:7517  tgid:7515 
> ppid:6054   flags:0x00000006
> Call Trace:
>  <TASK>
>  context_switch kernel/sched/core.c:5408 [inline]
>  __schedule+0x1796/0x49d0 kernel/sched/core.c:6745
>  __schedule_loop kernel/sched/core.c:6822 [inline]
>  schedule+0x14b/0x320 kernel/sched/core.c:6837
>  schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6894
>  __mutex_lock_common kernel/locking/mutex.c:684 [inline]
>  __mutex_lock+0x6a4/0xd70 kernel/locking/mutex.c:752
>  nfsd_nl_rpc_status_get_start+0x8d/0xe0 fs/nfsd/nfsctl.c:1476
>  genl_start+0x4d6/0x6d0 net/netlink/genetlink.c:1005
>  __netlink_dump_start+0x45c/0x780 net/netlink/af_netlink.c:2445
>  genl_family_rcv_msg_dumpit net/netlink/genetlink.c:1076 [inline]
>  genl_family_rcv_msg net/netlink/genetlink.c:1192 [inline]
>  genl_rcv_msg+0x88c/0xec0 net/netlink/genetlink.c:1210
>  netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2564
>  genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
>  netlink_unicast_kernel net/netlink/af_netlink.c:1335 [inline]
>  netlink_unicast+0x7ea/0x980 net/netlink/af_netlink.c:1361
>  netlink_sendmsg+0x8db/0xcb0 net/netlink/af_netlink.c:1905
>  sock_sendmsg_nosec net/socket.c:730 [inline]
>  __sock_sendmsg+0x221/0x270 net/socket.c:745
>  ____sys_sendmsg+0x525/0x7d0 net/socket.c:2585
>  ___sys_sendmsg net/socket.c:2639 [inline]
>  __sys_sendmsg+0x2b0/0x3a0 net/socket.c:2668
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f182b67cea9
> RSP: 002b:00007f182c48a0c8 EFLAGS: 00000246 ORIG_RAX:
> 000000000000002e
> RAX: ffffffffffffffda RBX: 00007f182b7b3f80 RCX: 00007f182b67cea9
> RDX: 0000000000000000 RSI: 0000000020000180 RDI: 0000000000000003
> RBP: 00007f182b6ebff4 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000000000b R14: 00007f182b7b3f80 R15: 00007ffd83adb8d8
>  </TASK>
> 
> Showing all locks held in the system:
> 5 locks held by kworker/u8:1/12:
>  #0: ffff888015ed3148 ((wq_completion)netns){+.+.}-{0:0}, at:
> process_one_work kernel/workqueue.c:3206 [inline]
>  #0: ffff888015ed3148 ((wq_completion)netns){+.+.}-{0:0}, at:
> process_scheduled_works+0x90a/0x1830 kernel/workqueue.c:3312
>  #1: ffffc90000117d00 (net_cleanup_work){+.+.}-{0:0}, at:
> process_one_work kernel/workqueue.c:3207 [inline]
>  #1: ffffc90000117d00 (net_cleanup_work){+.+.}-{0:0}, at:
> process_scheduled_works+0x945/0x1830 kernel/workqueue.c:3312
>  #2: ffffffff8f5c8cd0 (pernet_ops_rwsem){++++}-{3:3}, at:
> cleanup_net+0x16a/0xcc0 net/core/net_namespace.c:594
>  #3: ffff8880237ed408 (&wg->device_update_lock){+.+.}-{3:3}, at:
> wg_destruct+0x110/0x2e0 drivers/net/wireguard/device.c:249
>  #4: ffffffff8e339240 (rcu_state.barrier_mutex){+.+.}-{3:3}, at:
> rcu_barrier+0x4c/0x530 kernel/rcu/tree.c:4448
> 1 lock held by khungtaskd/30:
>  #0: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at:
> rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
>  #0: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock
> include/linux/rcupdate.h:781 [inline]
>  #0: ffffffff8e333fa0 (rcu_read_lock){....}-{1:2}, at:
> debug_show_all_locks+0x55/0x2a0 kernel/locking/lockdep.c:6614
> 3 locks held by kworker/u8:4/61:
>  #0: ffff8880b953e798 (&rq->__lock){-.-.}-{2:2}, at:
> raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:559
>  #1: ffff8880b9528948 (&per_cpu_ptr(group->pcpu, cpu)->seq){-.-.}-
> {0:0}, at: psi_task_switch+0x441/0x770 kernel/sched/psi.c:988
>  #2: ffff8880b953e798 (&rq->__lock){-.-.}-{2:2}, at:
> raw_spin_rq_lock_nested+0x2a/0x140 kernel/sched/core.c:559
> 3 locks held by kworker/0:2/1156:
>  #0: ffff888015080948 ((wq_completion)events){+.+.}-{0:0}, at:
> process_one_work kernel/workqueue.c:3206 [inline]
>  #0: ffff888015080948 ((wq_completion)events){+.+.}-{0:0}, at:
> process_scheduled_works+0x90a/0x1830 kernel/workqueue.c:3312
>  #1: ffffc90004627d00 ((linkwatch_work).work){+.+.}-{0:0}, at:
> process_one_work kernel/workqueue.c:3207 [inline]
>  #1: ffffc90004627d00 ((linkwatch_work).work){+.+.}-{0:0}, at:
> process_scheduled_works+0x945/0x1830 kernel/workqueue.c:3312
>  #2: ffffffff8f5d5508 (rtnl_mutex){+.+.}-{3:3}, at:
> linkwatch_event+0xe/0x60 net/core/link_watch.c:276
> 2 locks held by kworker/u8:9/2839:
> 2 locks held by getty/4842:
>  #0: ffff88802b04c0a0 (&tty->ldisc_sem){++++}-{0:0}, at:
> tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
>  #1: ffffc90002f162f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at:
> n_tty_read+0x6b5/0x1e10 drivers/tty/n_tty.c:2201
> 2 locks held by syz-fuzzer/5088:
> 3 locks held by kworker/0:6/5164:
>  #0: ffff888015080948 ((wq_completion)events){+.+.}-{0:0}, at:
> process_one_work kernel/workqueue.c:3206 [inline]
>  #0: ffff888015080948 ((wq_completion)events){+.+.}-{0:0}, at:
> process_scheduled_works+0x90a/0x1830 kernel/workqueue.c:3312
>  #1: ffffc90004577d00 (free_ipc_work){+.+.}-{0:0}, at:
> process_one_work kernel/workqueue.c:3207 [inline]
>  #1: ffffc90004577d00 (free_ipc_work){+.+.}-{0:0}, at:
> process_scheduled_works+0x945/0x1830 kernel/workqueue.c:3312
>  #2: ffffffff8e339378 (rcu_state.exp_mutex){+.+.}-{3:3}, at:
> exp_funnel_lock kernel/rcu/tree_exp.h:291 [inline]
>  #2: ffffffff8e339378 (rcu_state.exp_mutex){+.+.}-{3:3}, at:
> synchronize_rcu_expedited+0x381/0x830 kernel/rcu/tree_exp.h:939
> 2 locks held by syz-executor.4/7353:
>  #0: ffffffff8f63b9d0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x19/0x40
> net/netlink/genetlink.c:1218
>  #1: ffffffff8e600748 (nfsd_mutex){+.+.}-{3:3}, at:
> nfsd_nl_listener_set_doit+0x12d/0x1a90 fs/nfsd/nfsctl.c:1966
> 3 locks held by syz-executor.1/7517:
>  #0: ffffffff8f63b9d0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x19/0x40
> net/netlink/genetlink.c:1218
>  #1: ffff888052998678 (nlk_cb_mutex-GENERIC){+.+.}-{3:3}, at:
> __netlink_dump_start+0x119/0x780 net/netlink/af_netlink.c:2418
>  #2: ffffffff8e600748 (nfsd_mutex){+.+.}-{3:3}, at:
> nfsd_nl_rpc_status_get_start+0x8d/0xe0 fs/nfsd/nfsctl.c:1476
> 2 locks held by syz-executor.1/10475:
>  #0: ffffffff8f5d5508 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock
> net/core/rtnetlink.c:79 [inline]
>  #0: ffffffff8f5d5508 (rtnl_mutex){+.+.}-{3:3}, at:
> rtnetlink_rcv_msg+0x842/0x1180 net/core/rtnetlink.c:6632
> 
> 
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nfsd_nl_rpc_status_get_dumpit grabs the nfsd_mutex in the ->start
netlink op, and then releases it in the ->done op. Is it possible that
something is causing ->done to not happen after ->start has?

-- 
Jeff Layton <jlayton@kernel.org>