On Thu, May 18, 2017 at 12:48:48PM +0200, Jan Kara wrote:
> XFS SEEK_HOLE implementation could miss a hole in an unwritten extent as
> can be seen by the following command:
>
> xfs_io -c "falloc 0 256k" -c "pwrite 0 56k" -c "pwrite 128k 8k"
> -c "seek -h 0" file
> wrote 57344/57344 bytes at offset 0
> 56 KiB, 14 ops; 0.0000 sec (49.312 MiB/sec and 12623.9856 ops/sec)
> wrote 8192/8192 bytes at offset 131072
> 8 KiB, 2 ops; 0.0000 sec (70.383 MiB/sec and 18018.0180 ops/sec)
> Whence Result
> HOLE 139264
>
> Where we can see that hole at offset 56k was just ignored by SEEK_HOLE
> implementation. The bug is in xfs_find_get_desired_pgoff() which does
> not properly detect the case when pages are not contiguous.
>
> Fix the problem by properly detecting when found page has larger offset
> than expected.
>
> CC: stable@xxxxxxxxxxxxxxx
> Fixes: d126d43f631f996daeee5006714fed914be32368
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
> fs/xfs/xfs_file.c | 29 +++++++++--------------------
> 1 file changed, 9 insertions(+), 20 deletions(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 35703a801372..f371812e20c6 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -1076,17 +1076,6 @@ xfs_find_get_desired_pgoff(
> break;
> }
>
> - /*
> - * At lease we found one page. If this is the first time we
> - * step into the loop, and if the first page index offset is
> - * greater than the given search offset, a hole was found.
> - */
> - if (type == HOLE_OFF && lastoff == startoff &&
> - lastoff < page_offset(pvec.pages[0])) {
> - found = true;
> - break;
> - }
> -
> for (i = 0; i < nr_pages; i++) {
> struct page *page = pvec.pages[i];
> loff_t b_offset;
> @@ -1098,18 +1087,18 @@ xfs_find_get_desired_pgoff(
> * file mapping. However, page->index will not change
> * because we have a reference on the page.
> *
> - * Searching done if the page index is out of range.
> - * If the current offset is not reaches the end of
> - * the specified search range, there should be a hole
> - * between them.
> + * If current page offset is beyond where we've ended,
> + * we've found a hole.
> */
> - if (page->index > end) {
> - if (type == HOLE_OFF && lastoff < endoff) {
> - *offset = lastoff;
> - found = true;
> - }
> + if (type == HOLE_OFF && lastoff < endoff &&
> + lastoff < page_offset(pvec.pages[i])) {
> + found = true;
> + *offset = lastoff;
> goto out;
> }
> + /* Searching done if the page index is out of range. */
> + if (page->index > end)
> + goto out;
>
> lock_page(page);
> /*
> --
> 2.12.0
>
> --
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