Re: syscall rmdir hangs with autofs

[Avi Kivity <avi@redhat.com>]

On 07/19/2010 11:39 AM, Sebastian Hetze wrote:
> Hi *,
>
> we are encountering occasional problems with autofs running inside
> an KVM guest.
>
> [1387441.969106] INFO: task automount:26560 blocked for more than 120 seconds.
> [1387441.969110] "echo 0>  /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [1387441.969112] automount     D e8510198     0 26560   2702 0x00000000
> [1387441.969117]  db0a1ef4 00000082 80000000 e8510198 0004ed69 c8266000 f6e85a40 00000000
> [1387441.969123]  c08455e0 c08455e0 f41157f0 f4115a88 c55315e0 00000000 c0207c0a db0a1ef0
> [1387441.969128]  f4115a88 f7222bbc f7222bb8 ffffffff db0a1f20 c05976ae db0a1f14 f41157f0
> [1387441.969133] Call Trace:
> [1387441.969140]  [<c0207c0a>] ? mntput_no_expire+0x1a/0xd0
> [1387441.969146]  [<c05976ae>] __mutex_lock_slowpath+0xbe/0x120
> [1387441.969149]  [<c05975d0>] mutex_lock+0x20/0x40
> [1387441.969152]  [<c01fbc82>] do_rmdir+0x52/0xe0
> [1387441.969155]  [<c059ae47>] ? do_page_fault+0x1d7/0x3a0
> [1387441.969158]  [<c01fbd70>] sys_rmdir+0x10/0x20
> [1387441.969161]  [<c01033cc>] syscall_call+0x7/0xb
>
> The block always occurs in sys_rmdir when automount tries to remove the
> mountpoint right after umounting the filesystem. There is an successful lstat()
> on the mountpoint directly precceeding the rmdir call.
>
> It looks like we are triggering some sort of race condition here.
>
> We are currently using 2.6.31-20-generic-pae ubuntu kernel in the 6 CPU guest,
> 2.6.34 vanilla and qemu-kvm-0.12.4 in the host. But the problem existed
> long before with all different combinations of guest/host/qemu versions.
> The virtual HD is if=ide,format=host_device,cache=none on an DRBD container
> on top of an LVM device. FS is ext3.
>
> Unfortunately, the problem is not easy reproduceable. It occurs every one
> or two weeks. But since the hanging system call blocks the whole filesystem
> we have to reboot the guest to get it into an useable state again.
>
> Any ideas what's going wrong here?
>
>    

Is there substantial I/O going on?

If not, it may be an autofs bug unrelated to kvm.

-- 
error compiling committee.c: too many arguments to function