2009-08-31 19:35:51

by Christoph Hellwig

Subject: [PATCH] ext4: fix cache flish in ext4_sync_file

We need to flush the write cache unconditionally in ->fsync, otherwise
writes into already allocated blocks can get lost. Writes into fully
allocated files are very common when using disk images for
virtualization, and without this fix can easily lose data after
an fdatasync, which is the typical implementation for a cache flush on
the virtual drive.


Signed-off-by: Christoph Hellwig <[email protected]>

Index: linux-2.6/fs/ext4/fsync.c
===================================================================
--- linux-2.6.orig/fs/ext4/fsync.c
+++ linux-2.6/fs/ext4/fsync.c
@@ -92,9 +92,9 @@ int ext4_sync_file(struct file *file, st
.nr_to_write = 0, /* sys_fsync did this */
};
ret = sync_inode(inode, &wbc);
- if (journal && (journal->j_flags & JBD2_BARRIER))
- blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
}
out:
+ if (journal && (journal->j_flags & JBD2_BARRIER))
+ blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
return ret;
}

2009-09-01 18:23:27

by Eric Sandeen

Subject: Re: [PATCH] ext4: fix cache flish in ext4_sync_file

Christoph Hellwig wrote:
> We need to flush the write cache unconditionally in ->fsync, otherwise
> writes into already allocated blocks can get lost. Writes into fully
> allocated files are very common when using disk images for
> virtualization, and without this fix can easily lose data after
> an fdatasync, which is the typical implementation for a cache flush on
> the virtual drive.
>
>
> Signed-off-by: Christoph Hellwig <[email protected]>

Fixing my old commit, I guess ;)

Seems right to me

Acked-by: Eric Sandeen <[email protected]>


> Index: linux-2.6/fs/ext4/fsync.c
> ===================================================================
> --- linux-2.6.orig/fs/ext4/fsync.c
> +++ linux-2.6/fs/ext4/fsync.c
> @@ -92,9 +92,9 @@ int ext4_sync_file(struct file *file, st
> .nr_to_write = 0, /* sys_fsync did this */
> };
> ret = sync_inode(inode, &wbc);
> - if (journal && (journal->j_flags & JBD2_BARRIER))
> - blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
> }
> out:
> + if (journal && (journal->j_flags & JBD2_BARRIER))
> + blkdev_issue_flush(inode->i_sb->s_bdev, NULL);
> return ret;
> }
> --
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2009-09-06 01:43:23

by Theodore Ts'o

Subject: Re: [PATCH] ext4: fix cache flish in ext4_sync_file

On Tue, Sep 01, 2009 at 01:23:27PM -0500, Eric Sandeen wrote:
> Christoph Hellwig wrote:
> > We need to flush the write cache unconditionally in ->fsync, otherwise
> > writes into already allocated blocks can get lost. Writes into fully
> > allocated files are very common when using disk images for
> > virtualization, and without this fix can easily lose data after
> > an fdatasync, which is the typical implementation for a cache flush on
> > the virtual drive.
> >
> >
> > Signed-off-by: Christoph Hellwig <[email protected]>
>
> Fixing my old commit, I guess ;)

Added to the ext4 patch queue (with the "flish" corrected to "flush")

- Ted