Re: INFO: task hung in nbd_ioctl

[Mike Christie]

On 09/30/2019 05:39 PM, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    bb2aee77 Add linux-next specific files for 20190926
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=13385ca3600000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e60af4ac5a01e964
> dashboard link:
> https://syzkaller.appspot.com/bug?extid=24c12fa8d218ed26011a
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12abc2a3600000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11712c05600000
> 
> The bug was bisected to:
> 
> commit e9e006f5fcf2bab59149cb38a48a4817c1b538b4
> Author: Mike Christie <mchristi@xxxxxxxxxx>
> Date:   Sun Aug 4 19:10:06 2019 +0000
> 
>     nbd: fix max number of supported devs
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1226f3c5600000
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=1126f3c5600000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1626f3c5600000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+24c12fa8d218ed26011a@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: e9e006f5fcf2 ("nbd: fix max number of supported devs")
> 
> INFO: task syz-executor390:8778 can't die for more than 143 seconds.
> syz-executor390 D27432  8778   8777 0x00004004
> Call Trace:
>  context_switch kernel/sched/core.c:3384 [inline]
>  __schedule+0x828/0x1c20 kernel/sched/core.c:4065
>  schedule+0xd9/0x260 kernel/sched/core.c:4132
>  schedule_timeout+0x717/0xc50 kernel/time/timer.c:1871
>  do_wait_for_common kernel/sched/completion.c:83 [inline]
>  __wait_for_common kernel/sched/completion.c:104 [inline]
>  wait_for_common kernel/sched/completion.c:115 [inline]
>  wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
>  flush_workqueue+0x40f/0x14c0 kernel/workqueue.c:2826
>  nbd_start_device_ioctl drivers/block/nbd.c:1272 [inline]
>  __nbd_ioctl drivers/block/nbd.c:1347 [inline]
>  nbd_ioctl+0xb2e/0xc44 drivers/block/nbd.c:1387
>  __blkdev_driver_ioctl block/ioctl.c:304 [inline]
>  blkdev_ioctl+0xedb/0x1c20 block/ioctl.c:606
>  block_ioctl+0xee/0x130 fs/block_dev.c:1954
>  vfs_ioctl fs/ioctl.c:47 [inline]
>  file_ioctl fs/ioctl.c:539 [inline]
>  do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
>  ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
>  __do_sys_ioctl fs/ioctl.c:750 [inline]
>  __se_sys_ioctl fs/ioctl.c:748 [inline]
>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
>  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4452d9
> Code: Bad RIP value.
> RSP: 002b:00007ffde928d288 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004452d9
> RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
> RBP: 0000000000000000 R08: 00000000004025b0 R09: 00000000004025b0
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402520
> R13: 00000000004025b0 R14: 0000000000000000 R15: 0000000000000000
> INFO: task syz-executor390:8778 blocked for more than 143 seconds.
>       Not tainted 5.3.0-next-20190926 #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> syz-executor390 D27432  8778   8777 0x00004004
> Call Trace:
>  context_switch kernel/sched/core.c:3384 [inline]
>  __schedule+0x828/0x1c20 kernel/sched/core.c:4065
>  schedule+0xd9/0x260 kernel/sched/core.c:4132
>  schedule_timeout+0x717/0xc50 kernel/time/timer.c:1871
>  do_wait_for_common kernel/sched/completion.c:83 [inline]
>  __wait_for_common kernel/sched/completion.c:104 [inline]
>  wait_for_common kernel/sched/completion.c:115 [inline]
>  wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
>  flush_workqueue+0x40f/0x14c0 kernel/workqueue.c:2826
>  nbd_start_device_ioctl drivers/block/nbd.c:1272 [inline]
>  __nbd_ioctl drivers/block/nbd.c:1347 [inline]
>  nbd_ioctl+0xb2e/0xc44 drivers/block/nbd.c:1387
>  __blkdev_driver_ioctl block/ioctl.c:304 [inline]
>  blkdev_ioctl+0xedb/0x1c20 block/ioctl.c:606
>  block_ioctl+0xee/0x130 fs/block_dev.c:1954
>  vfs_ioctl fs/ioctl.c:47 [inline]
>  file_ioctl fs/ioctl.c:539 [inline]
>  do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
>  ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
>  __do_sys_ioctl fs/ioctl.c:750 [inline]
>  __se_sys_ioctl fs/ioctl.c:748 [inline]
>  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
>  do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x4452d9
> Code: Bad RIP value.
> RSP: 002b:00007ffde928d288 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004452d9
> RDX: 0000000000000000 RSI: 000000000000ab03 RDI: 0000000000000004
> RBP: 0000000000000000 R08: 00000000004025b0 R09: 00000000004025b0
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402520
> R13: 00000000004025b0 R14: 0000000000000000 R15: 0000000000000000
> 

I will send a fix for this.

I had assumed that for every socket type a kernel_sock_shutdown would
break us out of sock_recvmsg call, but it looks like that's not the case.