cluster/afr: Enforce order in pre/post op

The xattrop order in pre/post op on all the subvols
is client-0, client-1... client-n where n is (replica-count - 1).
This order can lead to invalid split-brains if the brick
dies in the middle of xattrops.

Example: transaction completed pre-op, so on all the subvolumes
xattrs have '1' changelog. Now post-op is sent to both the subvols.
On subvol-0 change-log of client-0 is decremented to 0, before
decrementing change-log of client-1 to 0 the brick dies.
This change-log status on subvol-0 gives the meaning that a
change is done on subvol-0 successfully but on subvol-1 it failed.
Which is not what happened.
Changes done when the subvol-0 was down will lead to pending
change-log on subvol-1 for subvol-0. Which is correct.
When the subvol-0 is brought back up, the change-log will be in
split-brain state even when it is not a legitimate split-brain.

If the brick dies in the middle of xattrops it should remain fool.
Pre-op should perform xattrop of the local change-log first and
post-op should perform xattrop of the local change-log last.
In case of optimistic changelogs txn_changelog should be done
last on local if it succeeds, first if it fails.

Change-Id: Ib6eeb20cdc49b0b1fd2f454f25a9c8e08388c6e7
BUG: 765194
Signed-off-by: Pranith Kumar K <pranithk@gluster.com>
Reviewed-on: http://review.gluster.com/3226
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

1 files changed, 6 insertions, 7 deletions

diff --git a/xlators/cluster/afr/src/afr-common.c b/xlators/cluster/afr/src/afr-common.c
index 171137b910d..1d1ac088178 100644
--- a/xlators/cluster/afr/src/afr-common.c
+++ b/xlators/cluster/afr/src/afr-common.c
@@ -798,6 +798,8 @@ afr_local_transaction_cleanup (afr_local_t *local, xlator_t *this)
         priv = this->private;
 
         afr_matrix_cleanup (local->pending, priv->child_count);
+        afr_matrix_cleanup (local->transaction.txn_changelog,
+                            priv->child_count);
 
         if (local->internal_lock.locked_nodes)
                 GF_FREE (local->internal_lock.locked_nodes);
@@ -813,7 +815,6 @@ afr_local_transaction_cleanup (afr_local_t *local, xlator_t *this)
 
 
         GF_FREE (local->transaction.pre_op);
-        GF_FREE (local->transaction.child_errno);
         GF_FREE (local->transaction.eager_lock);
 
         GF_FREE (local->transaction.basename);
@@ -3924,12 +3925,10 @@ afr_transaction_local_init (afr_local_t *local, xlator_t *this)
         if (!local->pending)
                 goto out;
 
-        local->transaction.child_errno =
-                GF_CALLOC (sizeof (*local->transaction.child_errno),
-                           priv->child_count,
-                           gf_afr_mt_int32_t);
-        local->transaction.erase_pending = 1;
-
+        local->transaction.txn_changelog = afr_matrix_create (priv->child_count,
+                                                           AFR_NUM_CHANGE_LOGS);
+        if (!local->transaction.txn_changelog)
+                goto out;
         ret = 0;
 out:
         return ret;