xfs: block deltas in xfs_trans_unreserve_and_mod_sb must be positive

And to make that more clear, rearrange the code a bit and add asserts
and a comment.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 50d878d78a5e112abeec2d8fcb8eda24f092dcff..95921ad935477f1b53e0984dfa724fdee8ed4b71 100644 (file)
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -594,28 +594,38 @@ xfs_trans_unreserve_and_mod_sb(
 {
        struct xfs_mount        *mp = tp->t_mountp;
        bool                    rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
-       int64_t                 blkdelta = 0;
-       int64_t                 rtxdelta = 0;
+       int64_t                 blkdelta = tp->t_blk_res;
+       int64_t                 rtxdelta = tp->t_rtx_res;
        int64_t                 idelta = 0;
        int64_t                 ifreedelta = 0;
        int                     error;
 
-       /* calculate deltas */
-       if (tp->t_blk_res > 0)
-               blkdelta = tp->t_blk_res;
-       if ((tp->t_fdblocks_delta != 0) &&
-           (xfs_has_lazysbcount(mp) ||
-            (tp->t_flags & XFS_TRANS_SB_DIRTY)))
+       /*
+        * Calculate the deltas.
+        *
+        * t_fdblocks_delta and t_frextents_delta can be positive or negative:
+        *
+        *  - positive values indicate blocks freed in the transaction.
+        *  - negative values indicate blocks allocated in the transaction
+        *
+        * Negative values can only happen if the transaction has a block
+        * reservation that covers the allocated block.  The end result is
+        * that the calculated delta values must always be positive and we
+        * can only put back previous allocated or reserved blocks here.
+        */
+       ASSERT(tp->t_blk_res || tp->t_fdblocks_delta >= 0);
+       if (xfs_has_lazysbcount(mp) || (tp->t_flags & XFS_TRANS_SB_DIRTY)) {
                blkdelta += tp->t_fdblocks_delta;
+               ASSERT(blkdelta >= 0);
+       }
 
-       if (tp->t_rtx_res > 0)
-               rtxdelta = tp->t_rtx_res;
-       if ((tp->t_frextents_delta != 0) &&
-           (tp->t_flags & XFS_TRANS_SB_DIRTY))
+       ASSERT(tp->t_rtx_res || tp->t_frextents_delta >= 0);
+       if (tp->t_flags & XFS_TRANS_SB_DIRTY) {
                rtxdelta += tp->t_frextents_delta;
+               ASSERT(rtxdelta >= 0);
+       }
 
-       if (xfs_has_lazysbcount(mp) ||
-            (tp->t_flags & XFS_TRANS_SB_DIRTY)) {
+       if (xfs_has_lazysbcount(mp) || (tp->t_flags & XFS_TRANS_SB_DIRTY)) {
                idelta = tp->t_icount_delta;
                ifreedelta = tp->t_ifree_delta;
        }