glusterd: big lock - a coarse-grained locking to prevent races

There are primarily three lists that are part of glusterd process,
that are concurrently accessed. Namely, priv->volumes, priv->peers
and volinfo->bricks_list.

Big-lock approach
-----------------
WHAT IS IT?
Big lock is a coarse-grained lock which protects all three
lists, mentioned above, from racy access.

HOW DOES IT WORK?
At any given point in time, glusterd's thread(s) are in execution
_iff_ there is a preceding, inbound network event. Of course, the
sigwaiter thread and timer thread are exceptions.
A network event is an external trigger to glusterd, via the epoll
thread, in the form of POLLIN and POLLERR.
As long as we take the big-lock at all such entry points and yield
it when we are done, we are guaranteed that all the network events,
accessing the global lists, are serialised.

This amounts to holding the big lock at
- all the handlers of all the actors in glusterd. (POLLIN)
- all the cbks in glusterd. (POLLIN)
- rpc_notify (DISCONNECT event), if we access/modify
  one of the three lists. (POLLERR)

In the case of synctask'ized volume operations, we must remember that,
if we held the big lock for the entire duration of the handler,
we may block other non-synctask rpc actors from executing.
For eg, volume-start would block in PMAP SIGNIN, if done incorrectly.
To prevent this, we need to yield the big lock, when we yield the
synctask, and reacquire on waking up of the synctask.

Change-Id: Ib929f9905b55fb6c3fc27fefb497a26dba058e4f
BUG: 948686
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4784
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>

1 files changed, 31 insertions, 9 deletions

diff --git a/xlators/mgmt/glusterd/src/glusterd-utils.c b/xlators/mgmt/glusterd/src/glusterd-utils.c
index 6c5d0e2f..e2d46a6a 100644
--- a/xlators/mgmt/glusterd/src/glusterd-utils.c
+++ b/xlators/mgmt/glusterd/src/glusterd-utils.c
@@ -23,6 +23,7 @@
 #include "timer.h"
 #include "defaults.h"
 #include "compat.h"
+#include "syncop.h"
 #include "run.h"
 #include "compat-errno.h"
 #include "statedump.h"
@@ -1252,6 +1253,7 @@ glusterd_brick_connect (glusterd_volinfo_t  *volinfo,
         char                    socketpath[PATH_MAX] = {0};
         dict_t                  *options = NULL;
         struct rpc_clnt         *rpc = NULL;
+        glusterd_conf_t         *priv = THIS->private;
 
         GF_ASSERT (volinfo);
         GF_ASSERT (brickinfo);
@@ -1270,9 +1272,11 @@ glusterd_brick_connect (glusterd_volinfo_t  *volinfo,
                                                              socketpath, 600);
                 if (ret)
                         goto out;
+                synclock_unlock (&priv->big_lock);
                 ret = glusterd_rpc_create (&rpc, options,
                                            glusterd_brick_rpc_notify,
                                            brickinfo);
+                synclock_lock (&priv->big_lock);
                 if (ret)
                         goto out;
                 brickinfo->rpc = rpc;
@@ -1422,10 +1426,14 @@ glusterd_volume_start_glusterfs (glusterd_volinfo_t  *volinfo,
                 runner_add_arg (&runner, "--mem-accounting");
 
         runner_log (&runner, "", GF_LOG_DEBUG, "Starting GlusterFS");
-        if (wait)
+        if (wait) {
+                synclock_unlock (&priv->big_lock);
                 ret = runner_run (&runner);
-        else
+                synclock_lock (&priv->big_lock);
+
+        } else {
                 ret = runner_run_nowait (&runner);
+        }
 
         if (ret)
                 goto out;
@@ -2403,6 +2411,19 @@ out:
         return in;
 }
 
+int
+glusterd_spawn_daemons (void *opaque)
+{
+        glusterd_conf_t *conf = THIS->private;
+        gf_boolean_t    start_bricks = (long) opaque;
+
+        if (start_bricks)
+                glusterd_restart_bricks (conf);
+        glusterd_restart_gsyncds (conf);
+        glusterd_restart_rebalance (conf);
+        return 0;
+}
+
 void
 glusterd_do_volume_quorum_action (xlator_t *this, glusterd_volinfo_t *volinfo,
                                   gf_boolean_t meets_quorum)
@@ -3399,6 +3420,7 @@ glusterd_nodesvc_connect (char *server, char *socketpath) {
         int                     ret = 0;
         dict_t                  *options = NULL;
         struct rpc_clnt         *rpc = NULL;
+        glusterd_conf_t         *priv = THIS->private;
 
         rpc = glusterd_nodesvc_get_rpc (server);
 
@@ -3412,9 +3434,11 @@ glusterd_nodesvc_connect (char *server, char *socketpath) {
                                                              socketpath, 600);
                 if (ret)
                         goto out;
+                synclock_unlock (&priv->big_lock);
                 ret = glusterd_rpc_create (&rpc, options,
                                            glusterd_nodesvc_rpc_notify,
                                            server);
+                synclock_lock (&priv->big_lock);
                 if (ret)
                         goto out;
                 (void) glusterd_nodesvc_set_rpc (server, rpc);
@@ -4055,13 +4079,8 @@ glusterd_restart_bricks (glusterd_conf_t *conf)
                 if (volinfo->status != GLUSTERD_STATUS_STARTED)
                         continue;
                 start_nodesvcs = _gf_true;
-                if (glusterd_is_volume_in_server_quorum (volinfo)) {
-                        //these bricks will be restarted once the quorum is met
-                        continue;
-                }
-
                 list_for_each_entry (brickinfo, &volinfo->bricks, brick_list) {
-                        glusterd_brick_start (volinfo, brickinfo, _gf_true);
+                        glusterd_brick_start (volinfo, brickinfo, _gf_false);
                 }
         }
 
@@ -5577,7 +5596,9 @@ glusterd_start_gsync (glusterd_volinfo_t *master_vol, char *slave,
         runner_argprintf (&runner, ":%s", master_vol->volname);
         runner_add_args  (&runner, slave, "--config-set", "session-owner",
                           uuid_str, NULL);
+        synclock_unlock (&priv->big_lock);
         ret = runner_run (&runner);
+        synclock_lock (&priv->big_lock);
         if (ret == -1) {
                 errcode = -1;
                 goto out;
@@ -5588,7 +5609,9 @@ glusterd_start_gsync (glusterd_volinfo_t *master_vol, char *slave,
         runner_argprintf (&runner, "%s/"GSYNC_CONF, priv->workdir);
         runner_argprintf (&runner, ":%s", master_vol->volname);
         runner_add_arg   (&runner, slave);
+        synclock_unlock (&priv->big_lock);
         ret = runner_run (&runner);
+        synclock_lock (&priv->big_lock);
         if (ret == -1) {
                 gf_asprintf (op_errstr, GEOREP" start failed for %s %s",
                              master_vol->volname, slave);
@@ -6051,7 +6074,6 @@ glusterd_restart_rebalance (glusterd_conf_t *conf)
         return ret;
 }
 
-
 void
 glusterd_volinfo_reset_defrag_stats (glusterd_volinfo_t *volinfo)
 {