[BUG] umount does not work for disconected nfs mounts

[BUG] umount does not work for disconected nfs mounts

[Konstantin Khlebnikov]

commit 33cee6675edecbd27c0628f8b7c74c7d88fc02b2
http://git.kernel.org/?p=utils/util-linux/util-linux-ng.git;a=commitdiff;h=33cee6675edecbd27c0628f8b7c74c7d88fc02b2;hp=fde25e6be6e00a0998eb58b4b9d0d0b9ad65dbfd
"umount: allow unmounting loopdev specified by associated file"
broke umounting (by mountpoint) for broken nfs mounts,
because now umount always call stat() for target argument and umount hang inside nfs-rpc:

[<ffffffff8163df3f>] rpc_wait_bit_killable+0x1f/0x40
[<ffffffff8163eb85>] __rpc_execute+0xe5/0x2f0
[<ffffffff8163eebe>] rpc_execute+0x3e/0x50
[<ffffffff816372f0>] rpc_run_task+0x70/0x90
[<ffffffff816373fe>] rpc_call_sync+0x3e/0x70
[<ffffffff812228f3>] nfs3_rpc_wrapper.constprop.11+0x43/0x70
[<ffffffff81223bd2>] nfs3_proc_getattr+0x42/0x80
[<ffffffff81212955>] __nfs_revalidate_inode+0x95/0x1f0
[<ffffffff81212bf1>] nfs_revalidate_inode+0x31/0x60
[<ffffffff81212cca>] nfs_getattr+0x5a/0x110
[<ffffffff8112caea>] vfs_getattr+0x1a/0x30
[<ffffffff8112cce3>] vfs_fstatat+0x53/0x70
[<ffffffff8112cd36>] vfs_stat+0x16/0x20
[<ffffffff8112d0c5>] sys_newstat+0x15/0x30
[<ffffffff816c45bb>] tracesys+0xd9/0xde
[<ffffffffffffffff>] 0xffffffffffffffff

so mount /mnt/nfs get stuck, umounting by device is still possible.

Re: [BUG] umount does not work for disconected nfs mounts

[Petr Uzel]

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On Tue, Jun 28, 2011 at 12:18:03PM +0400, Konstantin Khlebnikov wrote:
> commit 33cee6675edecbd27c0628f8b7c74c7d88fc02b2
> http://git.kernel.org/?p=utils/util-linux/util-linux-ng.git;a=commitdiff;h=33cee6675edecbd27c0628f8b7c74c7d88fc02b2;hp=fde25e6be6e00a0998eb58b4b9d0d0b9ad65dbfd
> "umount: allow unmounting loopdev specified by associated file"
> broke umounting (by mountpoint) for broken nfs mounts,
> because now umount always call stat() for target argument and umount hang inside nfs-rpc:
> 
> [<ffffffff8163df3f>] rpc_wait_bit_killable+0x1f/0x40
> [<ffffffff8163eb85>] __rpc_execute+0xe5/0x2f0
> [<ffffffff8163eebe>] rpc_execute+0x3e/0x50
> [<ffffffff816372f0>] rpc_run_task+0x70/0x90
> [<ffffffff816373fe>] rpc_call_sync+0x3e/0x70
> [<ffffffff812228f3>] nfs3_rpc_wrapper.constprop.11+0x43/0x70
> [<ffffffff81223bd2>] nfs3_proc_getattr+0x42/0x80
> [<ffffffff81212955>] __nfs_revalidate_inode+0x95/0x1f0
> [<ffffffff81212bf1>] nfs_revalidate_inode+0x31/0x60
> [<ffffffff81212cca>] nfs_getattr+0x5a/0x110
> [<ffffffff8112caea>] vfs_getattr+0x1a/0x30
> [<ffffffff8112cce3>] vfs_fstatat+0x53/0x70
> [<ffffffff8112cd36>] vfs_stat+0x16/0x20
> [<ffffffff8112d0c5>] sys_newstat+0x15/0x30
> [<ffffffff816c45bb>] tracesys+0xd9/0xde
> [<ffffffffffffffff>] 0xffffffffffffffff

Shouldn't this be handled in the kernel? Or is stat() really
supposed to fail in such way with broken nfs?

> 
> so mount /mnt/nfs get stuck, umounting by device is still possible.

We might first scan through mtab to check if umount arg is known
mountpoint and only if we fail, we would look for associated loopfile.

Karel?


Petr

--
Petr Uzel
IRC: ptr_uzl @ freenode

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Re: [BUG] umount does not work for disconected nfs mounts

[Konstantin Khlebnikov]

Petr Uzel wrote:
> On Tue, Jun 28, 2011 at 12:18:03PM +0400, Konstantin Khlebnikov wrote:
>> commit 33cee6675edecbd27c0628f8b7c74c7d88fc02b2
>> http://git.kernel.org/?p=utils/util-linux/util-linux-ng.git;a=commitdiff;h=33cee6675edecbd27c0628f8b7c74c7d88fc02b2;hp=fde25e6be6e00a0998eb58b4b9d0d0b9ad65dbfd
>> "umount: allow unmounting loopdev specified by associated file"
>> broke umounting (by mountpoint) for broken nfs mounts,
>> because now umount always call stat() for target argument and umount hang inside nfs-rpc:
>>
>> [<ffffffff8163df3f>] rpc_wait_bit_killable+0x1f/0x40
>> [<ffffffff8163eb85>] __rpc_execute+0xe5/0x2f0
>> [<ffffffff8163eebe>] rpc_execute+0x3e/0x50
>> [<ffffffff816372f0>] rpc_run_task+0x70/0x90
>> [<ffffffff816373fe>] rpc_call_sync+0x3e/0x70
>> [<ffffffff812228f3>] nfs3_rpc_wrapper.constprop.11+0x43/0x70
>> [<ffffffff81223bd2>] nfs3_proc_getattr+0x42/0x80
>> [<ffffffff81212955>] __nfs_revalidate_inode+0x95/0x1f0
>> [<ffffffff81212bf1>] nfs_revalidate_inode+0x31/0x60
>> [<ffffffff81212cca>] nfs_getattr+0x5a/0x110
>> [<ffffffff8112caea>] vfs_getattr+0x1a/0x30
>> [<ffffffff8112cce3>] vfs_fstatat+0x53/0x70
>> [<ffffffff8112cd36>] vfs_stat+0x16/0x20
>> [<ffffffff8112d0c5>] sys_newstat+0x15/0x30
>> [<ffffffff816c45bb>] tracesys+0xd9/0xde
>> [<ffffffffffffffff>] 0xffffffffffffffff
>
> Shouldn't this be handled in the kernel? Or is stat() really
> supposed to fail in such way with broken nfs?

It depends on used mount options, IIRR in "soft" mode it by default fail with EIO after 3-6 minutes timeout,
in "hard" mode syscalls never returns EIO.

BTW linux support bindmounting for individual files,
so argument can refer to regular file not only for loop device image.

>
>>
>> so mount /mnt/nfs get stuck, umounting by device is still possible.
>
> We might first scan through mtab to check if umount arg is known
> mountpoint and only if we fail, we would look for associated loopfile.

Yes, it seems is the best solution

>
> Karel?
>
>
> Petr
>
> --
> Petr Uzel
> IRC: ptr_uzl @ freenode

Re: [BUG] umount does not work for disconected nfs mounts

[Mike Frysinger]

On Tue, Jun 28, 2011 at 05:14, Konstantin Khlebnikov wrote:
> Petr Uzel wrote:
>> On Tue, Jun 28, 2011 at 12:18:03PM +0400, Konstantin Khlebnikov wrote:
>>> commit 33cee6675edecbd27c0628f8b7c74c7d88fc02b2
>>>
>>> http://git.kernel.org/?p=utils/util-linux/util-linux-ng.git;a=commitdiff;h=33cee6675edecbd27c0628f8b7c74c7d88fc02b2;hp=fde25e6be6e00a0998eb58b4b9d0d0b9ad65dbfd
>>> "umount: allow unmounting loopdev specified by associated file"
>>> broke umounting (by mountpoint) for broken nfs mounts,
>>> because now umount always call stat() for target argument and umount hang
>>> inside nfs-rpc:
>>
>> Shouldn't this be handled in the kernel? Or is stat() really
>> supposed to fail in such way with broken nfs?
>
> It depends on used mount options, IIRR in "soft" mode it by default fail
> with EIO after 3-6 minutes timeout,
> in "hard" mode syscalls never returns EIO.

i noticed this recently.  one of the reasons i love `umount -lf` with
broken nfs mounts is that it works immediately.  any attempt to access
said broken mount in this situation is wrong as it inherently implies
it has to wait for a timeout (if one ever comes as Konstantin noted).

other than my personal usage on the command line, it makes shutdown
scripts obnoxiously slow to the point of being useless.
-mike

Re: [BUG] umount does not work for disconected nfs mounts

[Karel Zak]

On Tue, Jun 28, 2011 at 10:57:24AM +0200, Petr Uzel wrote:
> > so mount /mnt/nfs get stuck, umounting by device is still possible.
> 
> We might first scan through mtab to check if umount arg is known
> mountpoint and only if we fail, we would look for associated loopfile.

 Yes, go ahead.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com