[PATCH] xfs: fix bogus space reservation in xfs_iomap_write_allocate

[Christoph Hellwig <hch@xxxxxx>]

The space reservations was without an explaination back in commit

    "Add error reporting calls in error paths that return EFSCORRUPTED"

back in 2003.  There is no reason to reserve disk blocks in the
transaction when allocating blocks for delalloc space as we already
reserved the space when creating the delalloc extent.

With this fix we stop running out of the reserved pool in generic/229,
which has happened for long time with small blocksize file systems,
and has increased in severity with the new buffered write path.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 fs/xfs/xfs_iomap.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 2114d53..279353c 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -691,7 +691,6 @@ xfs_iomap_write_allocate(
        xfs_trans_t     *tp;
        int             nimaps;
        int             error = 0;
-       int             nres;
 
        /*
         * Make sure that the dquots are there.
@@ -715,12 +714,15 @@ xfs_iomap_write_allocate(
                 * is in the delayed allocation extent on which we sit
                 * but before our buffer starts.
                 */
-
                nimaps = 0;
                while (nimaps == 0) {
-                       nres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
-
-                       error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, nres,
+                       /*
+                        * We have already reserved space for the extent and any
+                        * indirect blocks when creating the delalloc extent,
+                        * there is no need to reserve space in this transaction
+                        * again.
+                        */
+                       error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0,
                                        0, XFS_TRANS_RESERVE, &tp);
                        if (error)
                                return error;
@@ -783,7 +785,7 @@ xfs_iomap_write_allocate(
                         */
                        error = xfs_bmapi_write(tp, ip, map_start_fsb,
                                                count_fsb, 0, &first_block,
-                                               nres, imap, &nimaps,
+                                               0, imap, &nimaps,
                                                &dfops);
                        if (error)
                                goto trans_cancel;
-- 
2.1.4