1 files changed, 41 insertions, 13 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 1cd2ac163877..42975cb9e538 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -3179,29 +3179,57 @@ xlog_ticket_get(xlog_t		*log,
          * and their unit amount is the total amount of space required.
          *
          * The following lines of code account for non-transaction data
-         * which occupy space in the on-disk log. 
+         * which occupy space in the on-disk log.
+         *
+         * Normal form of a transaction is:
+         * <oph><trans-hdr><start-oph><reg1-oph><reg1><reg2-oph>...<commit-oph>
+         * and then there are LR hdrs, split-recs and roundoff at end of syncs.
+         *
+         * We need to account for all the leadup data and trailer data
+         * around the transaction data.
+         * And then we need to account for the worst case in terms of using
+         * more space.
+         * The worst case will happen if:
+         * - the placement of the transaction happens to be such that the
+         *   roundoff is at its maximum
+         * - the transaction data is synced before the commit record is synced
+         *   i.e. <transaction-data><roundoff> | <commit-rec><roundoff>
+         *   Therefore the commit record is in its own Log Record.
+         *   This can happen as the commit record is called with its
+         *   own region to xlog_write().
+         *   This then means that in the worst case, roundoff can happen for
+         *   the commit-rec as well.
+         *   The commit-rec is smaller than padding in this scenario and so it is
+         *   not added separately.
          */
 
+        /* for trans header */
+        unit_bytes += sizeof(xlog_op_header_t);
+        unit_bytes += sizeof(xfs_trans_header_t);
+
         /* for start-rec */
-        unit_bytes += sizeof(xlog_op_header_t); 
+        unit_bytes += sizeof(xlog_op_header_t);
+
+        /* for LR headers */
+        num_headers = ((unit_bytes + log->l_iclog_size-1) >> log->l_iclog_size_log);
+        unit_bytes += log->l_iclog_hsize * num_headers;
 
-        /* for padding */
+        /* for commit-rec LR header - note: padding will subsume the ophdr */
+        unit_bytes += log->l_iclog_hsize;
+
+        /* for split-recs - ophdrs added when data split over LRs */
+        unit_bytes += sizeof(xlog_op_header_t) * num_headers;
+
+        /* for roundoff padding for transaction data and one for commit record */
         if (XFS_SB_VERSION_HASLOGV2(&log->l_mp->m_sb) &&
-                log->l_mp->m_sb.sb_logsunit > 1) {
+            log->l_mp->m_sb.sb_logsunit > 1) {
                 /* log su roundoff */
-                unit_bytes += log->l_mp->m_sb.sb_logsunit;  
+                unit_bytes += 2*log->l_mp->m_sb.sb_logsunit;
         } else {
                 /* BB roundoff */
-                unit_bytes += BBSIZE;
+                unit_bytes += 2*BBSIZE;
         }
 
-        /* for commit-rec */
-        unit_bytes += sizeof(xlog_op_header_t);
- 
-        /* for LR headers */
-        num_headers = ((unit_bytes + log->l_iclog_size-1) >> log->l_iclog_size_log);
-        unit_bytes += log->l_iclog_hsize * num_headers;
-
         tic->t_unit_res         = unit_bytes;
         tic->t_curr_res         = unit_bytes;
         tic->t_cnt              = cnt;