[PATCH 6.1 CANDIDATE 08/19] xfs: handle nimaps=0 from xfs_bmapi_write in xfs_alloc_file_space

From: Christoph Hellwig <[email protected]>

[ Upstream commit 35dc55b9e80cb9ec4bcb969302000b002b2ed850 ]

If xfs_bmapi_write finds a delalloc extent at the requested range, it
tries to convert the entire delalloc extent to a real allocation.

But if the allocator cannot find a single free extent large enough to
cover the start block of the requested range, xfs_bmapi_write will
return 0 but leave *nimaps set to 0.

In that case we simply need to keep looping with the same startoffset_fsb
so that one of the following allocations will eventually reach the
requested range.

Note that this could affect any caller of xfs_bmapi_write that covers
an existing delayed allocation.  As far as I can tell we do not have
any other such caller, though - the regular writeback path uses
xfs_bmapi_convert_delalloc to convert delayed allocations to real ones,
and direct I/O invalidates the page cache first.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: "Darrick J. Wong" <[email protected]>
Signed-off-by: Chandan Babu R <[email protected]>
Signed-off-by: Leah Rumancik <[email protected]>
---
 fs/xfs/xfs_bmap_util.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index ce8e17ab5434..468bb61a5e46 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -778,49 +778,47 @@ xfs_alloc_file_space(
 	xfs_off_t		offset,
 	xfs_off_t		len)
 {
 	xfs_mount_t		*mp = ip->i_mount;
 	xfs_off_t		count;
-	xfs_filblks_t		allocated_fsb;
 	xfs_filblks_t		allocatesize_fsb;
 	xfs_extlen_t		extsz, temp;
 	xfs_fileoff_t		startoffset_fsb;
 	xfs_fileoff_t		endoffset_fsb;
-	int			nimaps;
 	int			rt;
 	xfs_trans_t		*tp;
 	xfs_bmbt_irec_t		imaps[1], *imapp;
 	int			error;
 
 	trace_xfs_alloc_file_space(ip);
 
 	if (xfs_is_shutdown(mp))
 		return -EIO;
 
 	error = xfs_qm_dqattach(ip);
 	if (error)
 		return error;
 
 	if (len <= 0)
 		return -EINVAL;
 
 	rt = XFS_IS_REALTIME_INODE(ip);
 	extsz = xfs_get_extsz_hint(ip);
 
 	count = len;
 	imapp = &imaps[0];
-	nimaps = 1;
 	startoffset_fsb	= XFS_B_TO_FSBT(mp, offset);
 	endoffset_fsb = XFS_B_TO_FSB(mp, offset + count);
 	allocatesize_fsb = endoffset_fsb - startoffset_fsb;
 
 	/*
 	 * Allocate file space until done or until there is an error
 	 */
 	while (allocatesize_fsb && !error) {
 		xfs_fileoff_t	s, e;
 		unsigned int	dblocks, rblocks, resblks;
+		int		nimaps = 1;
 
 		/*
 		 * Determine space reservations for data/realtime.
 		 */
 		if (unlikely(extsz)) {
@@ -882,19 +880,23 @@ xfs_alloc_file_space(
 		error = xfs_trans_commit(tp);
 		xfs_iunlock(ip, XFS_ILOCK_EXCL);
 		if (error)
 			break;
 
-		allocated_fsb = imapp->br_blockcount;
-
-		if (nimaps == 0) {
-			error = -ENOSPC;
-			break;
+		/*
+		 * If the allocator cannot find a single free extent large
+		 * enough to cover the start block of the requested range,
+		 * xfs_bmapi_write will return 0 but leave *nimaps set to 0.
+		 *
+		 * In that case we simply need to keep looping with the same
+		 * startoffset_fsb so that one of the following allocations
+		 * will eventually reach the requested range.
+		 */
+		if (nimaps) {
+			startoffset_fsb += imapp->br_blockcount;
+			allocatesize_fsb -= imapp->br_blockcount;
 		}
-
-		startoffset_fsb += allocated_fsb;
-		allocatesize_fsb -= allocated_fsb;
 	}
 
 	return error;
 
 error:
-- 
2.48.1.262.g85cc9f2d1e-goog