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Commit 5375023a authored by Jan Kara's avatar Jan Kara Committed by Darrick J. Wong
Browse files

xfs: Fix missed holes in SEEK_HOLE implementation 



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@vger.kernel.org
Fixes: d126d43f
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarBrian Foster <bfoster@redhat.com>
Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
parent 8affebe1

fs/xfs/xfs_file.c

+9 −20
Original line number Diff line number Diff line
@@ -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;

			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);

			/*