Subject: [syzbot] [kvm?] [net?] [virt?] INFO: task hung in __vhost_worker_flush

From: syzbot <[email-masked]>
Date: Wed, 29 May 2024 15:08:28 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    9b62e02e6336 Merge tag 'mm-hotfixes-stable-2024-05-25-09-1..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16cb0eec980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3e73beba72b96506
dashboard link: https://syzkaller.appspot.com/bug?extid=7f3bbe59e8dd2328a990
compiler:       gcc (Debian 12.2.0-14) 12.2.0, 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/61b507f6e56c/disk-9b62e02e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6991f1313243/vmlinux-9b62e02e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/65f88b96d046/bzImage-9b62e02e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

INFO: task syz-executor.2:9163 blocked for more than 143 seconds.
      Not tainted 6.9.0-syzkaller-12393-g9b62e02e6336 #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor.2  state:D stack:27024 pid:9163  tgid:9163  ppid:8496   flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5408 [inline]
 __schedule+0xf15/0x5d00 kernel/sched/core.c:6745
 __schedule_loop kernel/sched/core.c:6822 [inline]
 schedule+0xe7/0x350 kernel/sched/core.c:6837
 schedule_timeout+0x258/0x2a0 kernel/time/timer.c:2557
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common+0x3de/0x5f0 kernel/sched/completion.c:116
 __vhost_worker_flush+0x1aa/0x1e0 drivers/vhost/vhost.c:288
 vhost_worker_flush drivers/vhost/vhost.c:295 [inline]
 vhost_dev_flush+0xad/0x120 drivers/vhost/vhost.c:305
 vhost_vsock_flush drivers/vhost/vsock.c:694 [inline]
 vhost_vsock_dev_release+0x1a5/0x400 drivers/vhost/vsock.c:746
 __fput+0x408/0xbb0 fs/file_table.c:422
 __fput_sync+0x47/0x50 fs/file_table.c:507
 __do_sys_close fs/open.c:1555 [inline]
 __se_sys_close fs/open.c:1540 [inline]
 __x64_sys_close+0x86/0x100 fs/open.c:1540
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f910027bdda
RSP: 002b:00007ffc83a68930 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 0000000000000007 RCX: 00007f910027bdda
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 00007f91003ad980 R08: 0000001b2ec20000 R09: 00000000000003f6
R10: 000000008ae9c606 R11: 0000000000000293 R12: 0000000000056292
R13: 00007f91003abf8c R14: 00007ffc83a68a30 R15: 0000000000000032
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/30:
 #0: ffffffff8dbb18e0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:329 [inline]
 #0: ffffffff8dbb18e0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:781 [inline]
 #0: ffffffff8dbb18e0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x75/0x340 kernel/locking/lockdep.c:6614
2 locks held by kworker/u8:3/51:
 #0: ffff8880196fe948 ((wq_completion)iou_exit){+.+.}-{0:0}, at: process_one_work+0x12bf/0x1b60 kernel/workqueue.c:3206
 #1: ffffc90000bc7d80 ((work_completion)(&ctx->exit_work)){+.+.}-{0:0}, at: process_one_work+0x957/0x1b60 kernel/workqueue.c:3207
3 locks held by kworker/u8:6/1041:
 #0: ffff888029f54148 ((wq_completion)ipv6_addrconf){+.+.}-{0:0}, at: process_one_work+0x12bf/0x1b60 kernel/workqueue.c:3206
 #1: ffffc90004507d80 ((work_completion)(&(&ifa->dad_work)->work)){+.+.}-{0:0}, at: process_one_work+0x957/0x1b60 kernel/workqueue.c:3207
 #2: ffffffff8f74afa8 (rtnl_mutex){+.+.}-{3:3}, at: addrconf_dad_work+0xcf/0x1500 net/ipv6/addrconf.c:4193
2 locks held by kworker/u8:8/1261:
2 locks held by getty/4844:
 #0: ffff88802b1860a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
 #1: ffffc90002f062f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0xfc8/0x1490 drivers/tty/n_tty.c:2201
2 locks held by syz-fuzzer/7666:
3 locks held by syz-executor.1/9466:
 #0: ffff88802ce84d88 (&hdev->req_lock){+.+.}-{3:3}, at: hci_dev_do_close+0x26/0x90 net/bluetooth/hci_core.c:554
 #1: ffff88802ce84078 (&hdev->lock){+.+.}-{3:3}, at: hci_dev_close_sync+0x339/0x1100 net/bluetooth/hci_sync.c:5050
 #2: ffffffff8dbbd078 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock+0x1a4/0x3b0 kernel/rcu/tree_exp.h:323
1 lock held by syz-executor.3/11000:
 #0: ffffffff8f74afa8 (rtnl_mutex){+.+.}-{3:3}, at: tun_detach drivers/net/tun.c:698 [inline]
 #0: ffffffff8f74afa8 (rtnl_mutex){+.+.}-{3:3}, at: tun_chr_close+0x3e/0x250 drivers/net/tun.c:3500
1 lock held by syz-executor.3/11005:
 #0: ffffffff8f74afa8 (rtnl_mutex){+.+.}-{3:3}, at: tun_detach drivers/net/tun.c:698 [inline]
 #0: ffffffff8f74afa8 (rtnl_mutex){+.+.}-{3:3}, at: tun_chr_close+0x3e/0x250 drivers/net/tun.c:3500
1 lock held by syz-executor.4/11002:
 #0: ffffffff8f74afa8 (rtnl_mutex){+.+.}-{3:3}, at: tun_detach drivers/net/tun.c:698 [inline]
 #0: ffffffff8f74afa8 (rtnl_mutex){+.+.}-{3:3}, at: tun_chr_close+0x3e/0x250 drivers/net/tun.c:3500
1 lock held by syz-executor.1/11013:
 #0: ffffffff8f74afa8 (rtnl_mutex){+.+.}-{3:3}, at: __tun_chr_ioctl+0x4fc/0x4770 drivers/net/tun.c:3110

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