cluster/tier: do not block in synctask created from pause tier

We had run sleep() in the pause tier callback. Blocking within
a synctask is dangerous. The sleep() call does not inform
the synctask scheduler that a thread is no longer running.
It therefore believes it is running. If a second synctask already
exists, it may not be able to run. This occurs if the thread
limit in the pool has been reached.

Note the pool size only grows when a synctask is created, not
when it is moved from wait state to run state, as is the case
when an FOP completes. When the tier is paused during migration,
synctasks already exist waiting for responses to FOPs to the
server with high probability.

The fix is to yield() in the RPC callback, which will place
the synctask into the wait queue and free up a thread for the
FOP callback. A timer wakes the callback after sufficient
time has elapsed for the pause to occur.

Change-Id: I6a947ee04c6e5649946cb6d8207ba17263a67fc6
BUG: 1267950
Signed-off-by: Dan Lambright <dlambrig@redhat.com>
Reviewed-on: http://review.gluster.org/12987
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>

1 files changed, 49 insertions, 5 deletions

diff --git a/xlators/cluster/dht/src/tier.c b/xlators/cluster/dht/src/tier.c
index 10036368720..2f415c4dbc2 100644
--- a/xlators/cluster/dht/src/tier.c
+++ b/xlators/cluster/dht/src/tier.c
@@ -1374,10 +1374,8 @@ tier_start (xlator_t *this, gf_defrag_info_t *defrag)
                         goto out;
                 }
 
-                if (defrag->tier_conf.request_pause)
-                        defrag->tier_conf.paused = _gf_true;
-                else
-                        defrag->tier_conf.paused = _gf_false;
+                if (tier_conf->request_pause)
+                        gf_defrag_wake_pause_tier (tier_conf, _gf_true);
 
                 sleep(1);
 
@@ -1808,6 +1806,8 @@ tier_init (xlator_t *this)
 
         defrag->tier_conf.request_pause = 0;
 
+        pthread_mutex_init (&defrag->tier_conf.pause_mutex, 0);
+
         ret = dict_get_str (this->options,
                               "tier-pause", &paused);
 
@@ -1876,6 +1876,40 @@ out:
 
 
 int
+tier_cli_pause_done (int op_ret, call_frame_t *sync_frame, void *data)
+{
+        gf_msg ("tier", GF_LOG_INFO, 0,
+                DHT_MSG_TIER_PAUSED,
+                "Migrate file paused with op_ret %d", op_ret);
+
+        return op_ret;
+}
+
+int
+tier_cli_pause (void *data)
+{
+        gf_defrag_info_t        *defrag         = NULL;
+        xlator_t                *this           = NULL;
+        dht_conf_t              *conf           = NULL;
+        int                      ret            = -1;
+
+        this = data;
+
+        conf = this->private;
+        GF_VALIDATE_OR_GOTO (this->name, conf, exit);
+
+        defrag = conf->defrag;
+        GF_VALIDATE_OR_GOTO (this->name, defrag, exit);
+
+        gf_defrag_pause_tier (this, defrag);
+
+        ret = 0;
+exit:
+        return ret;
+}
+
+
+int
 tier_reconfigure (xlator_t *this, dict_t *options)
 {
         dht_conf_t       *conf           = NULL;
@@ -1884,6 +1918,7 @@ tier_reconfigure (xlator_t *this, dict_t *options)
         int               migrate_mb     = 0;
         gf_boolean_t      req_pause      = _gf_false;
         int               ret            = 0;
+        call_frame_t            *frame  = NULL;
 
         conf = this->private;
 
@@ -1932,7 +1967,16 @@ tier_reconfigure (xlator_t *this, dict_t *options)
                                   bool, out);
 
                 if (req_pause == _gf_true) {
-                        ret = gf_defrag_pause_tier (this, defrag);
+
+                        frame = create_frame (this, this->ctx->pool);
+                        if (!frame)
+                                goto out;
+
+                        frame->root->pid = GF_CLIENT_PID_DEFRAG;
+
+                        ret = synctask_new (this->ctx->env, tier_cli_pause,
+                                            tier_cli_pause_done, frame, this);
+
                         if (ret) {
                                 gf_msg (this->name, GF_LOG_ERROR, 0,
                                         DHT_MSG_LOG_TIER_ERROR,