libglusterfs: Fix a crash due to race between inode_ctx_set and inode_ref

Issue:
Currently inode ref count is guarded by inode_table->lock, and
inode_ctx is guarded by inode->lock. With the new patch [1]
inode_ref was modified to change the inode_ctx to track the ref
count per xlator. Thus inode_ref performed under inode_table->lock
is modifying inode_ctx which has to be modified only under inode->lock

Solution:
When a inode is created, inode_ctx holder is allocated for all the xlators.
Hence in case of inode_ctx_set instead of using the first free index in
inode ctx holder, we can have predecided index for every xlator in the graph.

Credits Pranith K <pkarampu@redhat.com>

[1] http://review.gluster.org/13736

> Reviewed-on: https://review.gluster.org/16622
> Smoke: Gluster Build System <jenkins@build.gluster.org>
> NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
> Reviewed-by: Niels de Vos <ndevos@redhat.com>
> CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
> Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>

Change-Id: I1bfe111c211fcc4fcd761bba01dc87c4c69b5170
BUG: 1423385
Signed-off-by: Poornima G <pgurusid@redhat.com>
Reviewed-on: https://review.gluster.org/16655
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>

4 files changed, 19 insertions, 34 deletions

diff --git a/libglusterfs/src/graph.c b/libglusterfs/src/graph.c
index 47f473a580f..0c7d6cf6101 100644
--- a/libglusterfs/src/graph.c
+++ b/libglusterfs/src/graph.c
@@ -111,6 +111,7 @@ glusterfs_graph_set_first (glusterfs_graph_t *graph, xlator_t *xl)
         graph->first = xl;
 
         graph->xl_count++;
+        xl->xl_id = graph->xl_count;
 }
 
 
diff --git a/libglusterfs/src/graph.y b/libglusterfs/src/graph.y
index e6a26058a06..7df3479d701 100644
--- a/libglusterfs/src/graph.y
+++ b/libglusterfs/src/graph.y
@@ -182,6 +182,7 @@ new_volume (char *name)
         construct->first = curr;
 
         construct->xl_count++;
+        curr->xl_id = construct->xl_count;
 
         gf_msg_trace ("parser", 0, "New node for '%s'", name);
 
diff --git a/libglusterfs/src/inode.c b/libglusterfs/src/inode.c
index d39a2194921..573ec03819a 100644
--- a/libglusterfs/src/inode.c
+++ b/libglusterfs/src/inode.c
@@ -451,21 +451,15 @@ static int
 __inode_get_xl_index (inode_t *inode, xlator_t *xlator)
 {
         int set_idx = -1;
-        int index   = 0;
-
-        for (index = 0; index < inode->table->ctxcount; index++) {
-                if (!inode->_ctx[index].xl_key) {
-                        if (set_idx == -1)
-                                set_idx = index;
-                        /* dont break, to check if key already exists
-                           further on */
-                }
-                if (inode->_ctx[index].xl_key == xlator) {
-                        set_idx = index;
-                        break;
-                }
-        }
 
+        if ((inode->_ctx[xlator->xl_id].xl_key != NULL) &&
+            (inode->_ctx[xlator->xl_id].xl_key != xlator))
+                goto out;
+
+        set_idx = xlator->xl_id;
+        inode->_ctx[set_idx].xl_key = xlator;
+
+out:
         return set_idx;
 }
 
@@ -2075,12 +2069,8 @@ __inode_ctx_get2 (inode_t *inode, xlator_t *xlator, uint64_t *value1,
         if (!inode || !xlator || !inode->_ctx)
                 goto out;
 
-        for (index = 0; index < inode->table->ctxcount; index++) {
-                if (inode->_ctx[index].xl_key == xlator)
-                        break;
-        }
-
-        if (index == inode->table->ctxcount)
+        index = xlator->xl_id;
+        if (inode->_ctx[index].xl_key != xlator)
                 goto out;
 
         if (inode->_ctx[index].value1) {
@@ -2196,13 +2186,8 @@ inode_ctx_del2 (inode_t *inode, xlator_t *xlator, uint64_t *value1,
                 if (!inode->_ctx)
                         goto unlock;
 
-                for (index = 0; index < inode->table->ctxcount;
-                     index++) {
-                        if (inode->_ctx[index].xl_key == xlator)
-                                break;
-                }
-
-                if (index == inode->table->ctxcount) {
+                index = xlator->xl_id;
+                if (inode->_ctx[index].xl_key != xlator) {
                         ret = -1;
                         goto unlock;
                 }
@@ -2242,13 +2227,8 @@ __inode_ctx_reset2 (inode_t *inode, xlator_t *xlator, uint64_t *value1,
 
         LOCK (&inode->lock);
         {
-                for (index = 0; index < inode->table->ctxcount;
-                     index++) {
-                        if (inode->_ctx[index].xl_key == xlator)
-                                break;
-                }
-
-                if (index == inode->table->ctxcount) {
+                index = xlator->xl_id;
+                if (inode->_ctx[index].xl_key != xlator) {
                         ret = -1;
                         goto unlock;
                 }
diff --git a/libglusterfs/src/xlator.h b/libglusterfs/src/xlator.h
index 1e2698bb61f..c2959efbd95 100644
--- a/libglusterfs/src/xlator.h
+++ b/libglusterfs/src/xlator.h
@@ -953,6 +953,9 @@ struct _xlator {
 
         /* Saved volfile ID (used for multiplexing) */
         char               *volfile_id;
+
+        /* Its used as an index to inode_ctx*/
+        uint32_t            xl_id;
 };
 
 typedef struct {