Fix: RCU read-side lock released too early in destroy_agent_app

[lttng-tools.git] / src / bin / lttng-sessiond / agent-thread.c

diff --git a/src/bin/lttng-sessiond/agent-thread.c b/src/bin/lttng-sessiond/agent-thread.c
index 1caf748432a4ec1918cab71a87b4788e02da1e47..9ac975cbf1ea9539c4d81db352089b25d12af561 100644 (file)
--- a/src/bin/lttng-sessiond/agent-thread.c
+++ b/src/bin/lttng-sessiond/agent-thread.c
@@ -16,6 +16,7 @@
  */
 
 #define _GNU_SOURCE
+#define _LGPL_SOURCE
 #include <assert.h>
 
 #include <common/common.h>
@@ -60,10 +61,12 @@ static void update_agent_app(struct agent_app *app)
                if (session->ust_session) {
                        struct agent *agt;
 
+                       rcu_read_lock();
                        agt = trace_ust_find_agent(session->ust_session, app->domain);
                        if (agt) {
                                agent_update(agt, app->sock->fd);
                        }
+                       rcu_read_unlock();
                }
                session_unlock(session);
        }
@@ -87,13 +90,13 @@ static void destroy_agent_app(int sock)
        rcu_read_lock();
        app = agent_find_app_by_sock(sock);
        assert(app);
-       rcu_read_unlock();
 
-       /* RCU read side lock is taken in this function call. */
+       /* RCU read side lock is assumed to be held by this function. */
        agent_delete_app(app);
 
        /* The application is freed in a RCU call but the socket is closed here. */
        agent_destroy_app(app);
+       rcu_read_unlock();
 }
 
 /*
@@ -304,12 +307,13 @@ void *agent_thread_manage_registration(void *data)
        }
 
        while (1) {
-               DBG3("[agent-thread] Manage agent polling on %d fds",
-                               LTTNG_POLL_GETNB(&events));
+               DBG3("[agent-thread] Manage agent polling");
 
                /* Inifinite blocking call, waiting for transmission */
 restart:
                ret = lttng_poll_wait(&events, -1);
+               DBG3("[agent-thread] Manage agent return from poll on %d fds",
+                               LTTNG_POLL_GETNB(&events));
                if (ret < 0) {
                        /*
                         * Restart interrupted system call.
@@ -327,6 +331,11 @@ restart:
                        revents = LTTNG_POLL_GETEV(&events, i);
                        pollfd = LTTNG_POLL_GETFD(&events, i);
 
+                       if (!revents) {
+                               /* No activity for this FD (poll implementation). */
+                               continue;
+                       }
+
                        /* Thread quit pipe has been closed. Killing thread. */
                        ret = sessiond_check_thread_quit_pipe(pollfd, revents);
                        if (ret) {