linux-kernel - Re: [dm-devel] [PATCH] deadlock with suspend and quotas

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Message-ID: <Pine.LNX.4.64.1111300143340.31264@hs20-bc2-1.build.redhat.com>
Date:	Wed, 30 Nov 2011 01:52:22 -0500 (EST)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Jan Kara <jack@...e.cz>
cc:	Alasdair G Kergon <agk@...hat.com>, esandeen@...hat.com,
	Surbhi Palande <csurbhi@...il.com>,
	linux-kernel@...r.kernel.org, dm-devel@...hat.com,
	linux-fsdevel@...r.kernel.org,
	Christopher Chaltain <christopher.chaltain@...onical.com>,
	Valerie Aurora <val@...consulting.com>
Subject: Re: [dm-devel] [PATCH] deadlock with suspend and quotas

> > dm-ioctl.h:
> > /*
> >  * Set this to avoid attempting to freeze any filesystem when suspending.
> >  */
> > #define DM_SKIP_LOCKFS_FLAG     (1 << 10) /* In */
>   Thanks. I was now checking in detail and indeed FIFREEZE fails if
> ->freeze_fs is not set. And only xfs, ext3, ext4, reiserfs, jfs, nilfs2,
> and gfs2 provide this function. So I was correct in assuming that when
> filesystem supports FIFREEZE it must make sure no modifications happen to
> the filesystem. So I believe that my original plan for sync to skip frozen
> filesystem is correct.
> 
> 								Honza

LVM doesn't suspend with FIFREEZE, it calls freeze_bdev directly from 
drivers/md/dm.c (and it works for all filesystems, including ext2). So if 
you skip sync of frozen filesystems, you introduce a data corruption if 
someone takes a snapshot of ext2.

Mikulas
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