linux-kernel - Re: Problem with multiple mounts

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Date:	Wed, 08 Nov 2006 14:38:58 -0800
From:	Suzuki <suzuki@...ux.vnet.ibm.com>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
CC:	reiserfs-list@...esys.com, lkml <linux-kernel@...r.kernel.org>,
	Jan Kara <jack@...e.cz>
Subject: Re: Problem with multiple mounts

Lennart Sorensen wrote:
> On Wed, Nov 08, 2006 at 11:22:15AM -0800, Suzuki wrote:
> 
>>"I exported a disk partition using nbd protocol. On the nbd client, I 
>>make reiserfs and run fsstress test case on this partition. At the same 
>>time, I mount this partition on the nbd server. Then Oops appears as 
>>following:"
>>
>>ReiserFS: sda10: found reiserfs format "3.6" with standard journal
>>ReiserFS: sda10: using ordered data mode
>>ReiserFS: sda10: journal params: device sda10, size 8192, journal first 
>>block 18, max trans len 1024, max batch 900, max commit age 30, max 
>>trans age 30
>>ReiserFS: sda10: checking transaction log (sda10)
>>
>>Oops: Kernel access of bad area, sig: 11 [#1]
>>
>>Call Trace:
>>[C000000011333090] [C0000000001EDB70] .journal_read+0x165c/0x1b6c 
>>(unreliable)
>>[C000000011333410] [C0000000001EF280] .journal_init+0xdc0/0xee8
>>[C000000011333530] [C0000000001CDBD8] .reiserfs_fill_super+0xa90/0x1e40
>>[C000000011333790] [C00000000011E988] .get_sb_bdev+0x208/0x31c
>>[C000000011333870] [C0000000001CA00C] .get_super_block+0x38/0x60
>>[C000000011333900] [C00000000011E260] .vfs_kern_mount+0xec/0x198
>>[C0000000113339B0] [C00000000011E3E0] .do_kern_mount+0x88/0xdc
>>[C000000011333A50] [C0000000001532CC] .do_mount+0xd50/0xe08
>>[C000000011333D60] [C000000000175090] .compat_sys_mount+0x368/0x448
>>[C000000011333E30] [C00000000000861C] syscall_exit+0x0/0x40
>>
>>But, if we try the steps in the reverse order,
>>
>>"mount the partition on nbd server first and then try fsstress tests on 
>>the client side. This is just to ensure that the server is not seeing an 
>>incomplete journal created by the client side runs."
>>
>>Things work fine !
>>
>>I doubt if this is due to the mount finding an incomplete journal 
>>created by the client side fsstress runs in the first scenario.
>>
>>My question is : Is this supported ? Mounting a filesystem which is 
>>already mounted and replaying the ( - a may be incomplete- ) journal.
> 
> 
> Absolutely not supported.  Unless you have a filesystem that is
> specifically designed for simultanious read-write mount from multiple
> places, then you can't.  For performance reasons most systems cache
> writes and updates in many cases, so the data read by one system may be
> out of date because another system has an update waiting to go to disk.
> You need a filesystem that has the ability for multiple systems to talk
> to each other about updates and locking and such things.  Look for a
> cluster supporting filesystem or whatever is used to refer to a
> filesystem that supports multiple hosts having it mounted to provide
> redundant access.  No normal filesystem can do it unless everyone has it
> mounted read only.  If you want to share it, use NFS.  That's what it's
> for.

Thanks for the response. This problem was reported by one of our test 
team on 2.6.19. So, I wanted to confirm that what they are doing is not 
supported !



Thanks,

Suzuki
> 
> --
> Len Sorensen

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