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Subject[PATCH 3.16 094/233] xfs: Fix missed holes in SEEK_HOLE implementation
3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@suse.cz>

commit 5375023ae1266553a7baa0845e82917d8803f48c upstream.

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.

Fixes: d126d43f631f996daeee5006714fed914be32368
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/xfs/xfs_file.c | 29 +++++++++--------------------
1 file changed, 9 insertions(+), 20 deletions(-)

--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1079,17 +1079,6 @@ 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;
@@ -1101,18 +1090,18 @@ 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);
/*
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