[XFS] use minleft when allocating in xfs_bmbt_split()

The bmap btree split code relies on a previous data extent allocation
(from xfs_bmap_btalloc()) to find an AG that has sufficient space to
perform a full btree split, when inserting the extent. When converting
unwritten extents we don't allocate a data extent so a btree split will be
the first allocation. In this case we need to set minleft so the allocator
will pick an AG that has space to complete the split(s).

SGI-PV: 983338

SGI-Modid: xfs-linux-melb:xfs-kern:31357a

Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: David Chinner <dgc@sgi.com>

diff --git a/fs/xfs/xfs_bmap_btree.c b/fs/xfs/xfs_bmap_btree.c
index 4aa2f11ba5638388cff7b70dbce6d7ad27f8cfde..3fc09cd8d5178152b15162a507aeaad3a5a56c65 100644 (file)
--- a/fs/xfs/xfs_bmap_btree.c
+++ b/fs/xfs/xfs_bmap_btree.c
@@ -1493,12 +1493,25 @@ xfs_bmbt_split(
        left = XFS_BUF_TO_BMBT_BLOCK(lbp);
        args.fsbno = cur->bc_private.b.firstblock;
        args.firstblock = args.fsbno;
+       args.minleft = 0;
        if (args.fsbno == NULLFSBLOCK) {
                args.fsbno = lbno;
                args.type = XFS_ALLOCTYPE_START_BNO;
+               /*
+                * Make sure there is sufficient room left in the AG to
+                * complete a full tree split for an extent insert.  If
+                * we are converting the middle part of an extent then
+                * we may need space for two tree splits.
+                *
+                * We are relying on the caller to make the correct block
+                * reservation for this operation to succeed.  If the
+                * reservation amount is insufficient then we may fail a
+                * block allocation here and corrupt the filesystem.
+                */
+               args.minleft = xfs_trans_get_block_res(args.tp);
        } else
                args.type = XFS_ALLOCTYPE_NEAR_BNO;
-       args.mod = args.minleft = args.alignment = args.total = args.isfl =
+       args.mod = args.alignment = args.total = args.isfl =
                args.userdata = args.minalignslop = 0;
        args.minlen = args.maxlen = args.prod = 1;
        args.wasdel = cur->bc_private.b.flags & XFS_BTCUR_BPRV_WASDEL;

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 7edcde691d1a2539e340db2e83769ad12188e6e6..67f22b2b44b3c41c51ce3ac6c1f911f5db47b181 100644 (file)
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -889,6 +889,16 @@ xfs_iomap_write_unwritten(
        count_fsb = XFS_B_TO_FSB(mp, (xfs_ufsize_t)offset + count);
        count_fsb = (xfs_filblks_t)(count_fsb - offset_fsb);
 
+       /*
+        * Reserve enough blocks in this transaction for two complete extent
+        * btree splits.  We may be converting the middle part of an unwritten
+        * extent and in this case we will insert two new extents in the btree
+        * each of which could cause a full split.
+        *
+        * This reservation amount will be used in the first call to
+        * xfs_bmbt_split() to select an AG with enough space to satisfy the
+        * rest of the operation.
+        */
        resblks = XFS_DIOSTRAT_SPACE_RES(mp, 0) << 1;
 
        do {