linux-ext4 - Re: [PATCH] ext4: don't read blocks from disk after extents being swapped in move_extent_per

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Date:	Fri, 12 Feb 2016 01:21:58 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Eryu Guan <guaneryu@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: don't read blocks from disk after extents being
 swapped in move_extent_per_page()

On Wed, Feb 10, 2016 at 11:16:45PM +0800, Eryu Guan wrote:
> I notice ext4/307 fails occasionally on ppc64 host, reporting md5
> checksum mismatch after moving data from original file to donor file.
> 
> The reason is that move_extent_per_page() calls __block_write_begin()
> and block_commit_write() to write saved data from original inode blocks
> to donor inode blocks, but __block_write_begin() not only maps buffer
> heads but also reads block content from disk if the size is not block
> size aligned. At this time the physical block number in mapped buffer
> head is pointing to the donor file not the original file, and that
> results in reading wrong data to page, which get written to disk in
> following block_commit_write call.

Thanks, applied.

					- Ted
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