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: 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>

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index aefa2134a8cbe01a032eaa77de159f6a21cf75b2..f1517e9928c76bab8fbe6816bfb501f5d5eeb3b5 100644 (file)
--- 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);
                        /*