[PATCH] xfs_bmap_add_extent_delay_real should set br_startblock to nullstartblock

[Ben Myers]

When filling in the middle of a previous delayed allocation in
xfs_bmap_add_extent_delay_real, set br_startblock of the new delay extent to
the right to nullstartblock instead of 0 before inserting the extent into the
ifork (xfs_iext_insert), rather than setting br_startblock afterward.

Adding the extent into the ifork with br_startblock=0 can lead to the extent
being copied into the btree by xfs_bmap_extent_to_btree if we happen to convert
from extents format to btree format before updating br_startblock with the
correct value.  The unexpected addition of this delay extent to the btree can
cause subsequent XFS_WANT_CORRUPTED_GOTO filesystem shutdown in several
xfs_bmap_add_extent_delay_real cases where we are converting a delay extent to
real and unexpectedly find an extent already inserted.  For example:

911         case BMAP_LEFT_FILLING:
912                 /*
913                  * Filling in the first part of a previous delayed allocation.
914                  * The left neighbor is not contiguous.
915                  */
916                 trace_xfs_bmap_pre_update(ip, idx, state, _THIS_IP_);
917                 xfs_bmbt_set_startoff(ep, new_endoff);
918                 temp = PREV.br_blockcount - new->br_blockcount;
919                 xfs_bmbt_set_blockcount(ep, temp);
920                 xfs_iext_insert(ip, idx, 1, new, state);
921                 ip->i_df.if_lastex = idx;
922                 ip->i_d.di_nextents++;
923                 if (cur == NULL)
924                         rval = XFS_ILOG_CORE | XFS_ILOG_DEXT;
925                 else {
926                         rval = XFS_ILOG_CORE;
927                         if ((error = xfs_bmbt_lookup_eq(cur, new->br_startoff,
928                                         new->br_startblock, new->br_blockcount,
929                                         &i)))
930                                 goto done;
931                         XFS_WANT_CORRUPTED_GOTO(i == 0, done);

With the bogus extent in the btree we shutdown the filesystem at 931.  The
conversion from extents to btree format happens when the number of extents in
the inode increases above ip->i_df.if_ext_max.  xfs_bmap_extent_to_btree copies
extents from the ifork into the btree, ignoring all delalloc extents which are
denoted by br_startblock having some value of nullstartblock.

SGI-PV: 1013221

Signed-off-by: Ben Myers <bpm at sgi.com>
---
 fs/xfs/xfs_bmap.c |   33 +++++++++++++++++++++++++--------
 1 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/fs/xfs/xfs_bmap.c b/fs/xfs/xfs_bmap.c
index 4111cd3..c1db779 100644
--- a/fs/xfs/xfs_bmap.c
+++ b/fs/xfs/xfs_bmap.c
@@ -1038,17 +1038,34 @@ xfs_bmap_add_extent_delay_real(
 		 * Filling in the middle part of a previous delayed allocation.
 		 * Contiguity is impossible here.
 		 * This case is avoided almost all the time.
+		 *
+		 * We start with a delayed allocation:
+		 *
+		 * +ddddddddddddddddddddddddddddddddddddddddddddddddddddddd+
+		 *  PREV @ idx
+		 *
+	         * and we are allocating:
+		 *                     +rrrrrrrrrrrrrrrrr+	 
+		 *			      new
+		 *
+		 * and we set it up for insertion as:
+		 * +ddddddddddddddddddd+rrrrrrrrrrrrrrrrr+ddddddddddddddddd+
+		 *                            new
+		 *  PREV @ idx          LEFT              RIGHT
+		 *                      inserted at idx + 1 
 		 */
 		temp = new->br_startoff - PREV.br_startoff;
-		trace_xfs_bmap_pre_update(ip, idx, 0, _THIS_IP_);
-		xfs_bmbt_set_blockcount(ep, temp);
-		r[0] = *new;
-		r[1].br_state = PREV.br_state;
-		r[1].br_startblock = 0;
-		r[1].br_startoff = new_endoff;
 		temp2 = PREV.br_startoff + PREV.br_blockcount - new_endoff;
-		r[1].br_blockcount = temp2;
-		xfs_iext_insert(ip, idx + 1, 2, &r[0], state);
+		trace_xfs_bmap_pre_update(ip, idx, 0, _THIS_IP_);
+		xfs_bmbt_set_blockcount(ep, temp);	/* truncate PREV */
+		LEFT = *new;
+		RIGHT.br_state = PREV.br_state;	
+		RIGHT.br_startblock = nullstartblock(
+				(int)xfs_bmap_worst_indlen(ip, temp2));
+		RIGHT.br_startoff = new_endoff;
+		RIGHT.br_blockcount = temp2;
+		/* insert LEFT (r[0]) and RIGHT (r[1]) at the same time */
+		xfs_iext_insert(ip, idx + 1, 2, &LEFT, state);
 		ip->i_df.if_lastex = idx + 1;
 		ip->i_d.di_nextents++;
 		if (cur == NULL)