On Thu, Aug 02, 2018 at 03:03:51PM -0500, Eric Sandeen wrote:
> The position calculation in iomap_bmap() shifts bno the wrong way,
> so we don't progress properly and end up re-mapping block zero
> over and over, yielding an unchanging physical block range as the
> logical block advances:
>
> # filefrag -Be file
> ext: logical_offset: physical_offset: length: expected: flags:
> 0: 0.. 0: 21.. 21: 1: merged
> 1: 1.. 1: 21.. 21: 1: 22: merged
> Discontinuity: Block 1 is at 21 (was 22)
> 2: 2.. 2: 21.. 21: 1: 22: merged
> Discontinuity: Block 2 is at 21 (was 22)
> 3: 3.. 3: 21.. 21: 1: 22: merged
>
> This breaks the FIBMAP interface for anyone using it (XFS), which
> in turn breaks LILO, zipl, etc.
>
> Bug-actually-spotted-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> Fixes: 89eb1906a953 ("iomap: add an iomap-based bmap implementation")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
>
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 77397b5a96ef..0d0bd8845586 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -1443,7 +1443,7 @@ iomap_bmap(struct address_space *mapping, sector_t bno,
> const struct iomap_ops *ops)
> {
> struct inode *inode = mapping->host;
> - loff_t pos = bno >> inode->i_blkbits;
> + loff_t pos = bno << inode->i_blkbits;
> unsigned blocksize = i_blocksize(inode);
>
> if (filemap_write_and_wait(mapping))
>
> --
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