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Date: Fri, 12 Nov 2010 16:27:00 +0200
From: Andriy Gapon <avg@freebsd.org>
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To: Alexander Zagrebin <alexz@visp.ru>
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Cc: freebsd-fs@freebsd.org, freebsd-stable@freebsd.org,
	Martin Matuska <mm@freebsd.org>
Subject: Re: 8.1-STABLE: problem with unmounting ZFS snapshots
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on 12/11/2010 16:00 Alexander Zagrebin said the following:
> Thanks for your reply!
> 
>>> 2. the umount is waiting for disk
>>> #ps | egrep 'PID|umount'
>>>   PID  TT  STAT      TIME COMMAND
>>>   958   0  D+     0:00,04 umount /mnt
>>> # procstat -t 958
>>>   PID    TID COMM             TDNAME           CPU  PRI 
>> STATE   WCHAN
>>>   958 100731 umount           -                  3  133 
>> sleep   mntref
>>
>> procstat -kk <pid>
> 
> $ ps a | grep umount
> 86874   2- D      0:00,06 umount /mnt
> 90433   3  S+     0:00,01 grep umount
> 
> $ sudo procstat -kk 86874
>   PID    TID COMM             TDNAME           KSTACK
> 86874 100731 umount           -                mi_switch+0x176
> sleepq_wait+0x42 _sleep+0x317 vfs_mount_destroy+0x5a dounmount+0x4d4
> unmount+0x38b syscall+0x1cf Xfast_syscall+0xe2
> 


Looks like possible mnt_ref leak.
I think that something like that was fixed some not long time ago.
Perhaps you either don't have the fix or there is another leak.
What revision do you have?

Perhaps Martin has an insight here.

-- 
Andriy Gapon