Do not call gpm_grab_sock() twice

In the gpm_get_ctx() call, we unnecessarily call gpm_grab_sock() which
would cause the lock to be held by one thread and never released.  We
already call gpm_grab_sock() as the first thing after gpm_get_ctx() in
gpm_make_call(), plus gpm_make_call() properly releases the socket
once done.

This corrects the deadlock fix in
461a5fa, which incorrectly released
the lock we wanted to grab.  This caused the socket to not be locked
to our thread.  Another thread could come along and change the global
ctx while we were still using the socket from another thread, causing
concurrency issues as only one request can be in flight on any given
socket at the same time.

In special cases where the "thread" uid/gid changes (like in
rpc.gssd), we end up closing the socket while we are still waiting for
an answer from the server, causing additional issues and confusion.

[[email protected]: squashed 2 commits; minor edits accordingly]
Signed-off-by: Simo Sorce <[email protected]>
Reviewed-by: Robbie Harwood <[email protected]>
Merges: #218
Signed-off-by: Robbie Harwood <[email protected]>

Author: simo5

src/client/gpm_common.c

@@ -163,7 +163,9 @@ static int gpm_grab_sock(struct gpm_ctx *gpmctx)
         ret = gpm_open_socket(gpmctx);
     }
 
-    pthread_mutex_unlock(&gpmctx->lock);
+    if (ret) {
+        pthread_mutex_unlock(&gpmctx->lock);
+    }
     return ret;
 }
 
@@ -518,11 +520,6 @@ static struct gpm_ctx *gpm_get_ctx(void)
 
     pthread_once(&gpm_init_once_control, gpm_init_once);
 
-    ret = gpm_grab_sock(&gpm_global_ctx);
-    if (ret) {
-        return NULL;
-    }
-
     return &gpm_global_ctx;
 }