From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 21 Dec 2016 22:59:38 +0000 (-0500)
Subject: Fix: add missing rcu_barrier before daemon teardown
X-Git-Tag: v2.8.6~2
X-Git-Url: https://git.liburcu.org/?p=lttng-tools.git;a=commitdiff_plain;h=19154d2ab25daef13e23586d1c5201b6baaf8148

Fix: add missing rcu_barrier before daemon teardown

When performing the "cleanup" of sessiond, consumerd, and relayd, we
destroy data structures that may still be concurrently accessed by
call_rcu worker thread.

Ensure no more work is present in the call_rcu worker thread by issuing
a rcu_barrier barrier. Note that this expects call_rcu handlers don't
chain work to other call_rcu handlers.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/bin/lttng-consumerd/lttng-consumerd.c b/src/bin/lttng-consumerd/lttng-consumerd.c
index 079bd6024..293654053 100644
--- a/src/bin/lttng-consumerd/lttng-consumerd.c
+++ b/src/bin/lttng-consumerd/lttng-consumerd.c
@@ -628,6 +628,12 @@ exit_init_data:
 	tmp_ctx = ctx;
 	ctx = NULL;
 	cmm_barrier();	/* Clear ctx for signal handler. */
+	/*
+	 * Wait for all pending call_rcu work to complete before tearing
+	 * down data structures. call_rcu worker may be trying to
+	 * perform lookups in those structures.
+	 */
+	rcu_barrier();
 	lttng_consumer_destroy(tmp_ctx);
 	lttng_consumer_cleanup();
 
diff --git a/src/bin/lttng-relayd/main.c b/src/bin/lttng-relayd/main.c
index 2714f783b..56efaae34 100644
--- a/src/bin/lttng-relayd/main.c
+++ b/src/bin/lttng-relayd/main.c
@@ -2944,6 +2944,12 @@ exit_init_data:
 	health_app_destroy(health_relayd);
 exit_health_app_create:
 exit_options:
+	/*
+	 * Wait for all pending call_rcu work to complete before tearing
+	 * down data structures. call_rcu worker may be trying to
+	 * perform lookups in those structures.
+	 */
+	rcu_barrier();
 	relayd_cleanup();
 
 	/* Ensure all prior call_rcu are done. */
diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index e810d5614..b29c6745b 100644
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -6221,6 +6221,12 @@ exit_client:
 exit_health:
 
 exit_init_data:
+	/*
+	 * Wait for all pending call_rcu work to complete before tearing
+	 * down data structures. call_rcu worker may be trying to
+	 * perform lookups in those structures.
+	 */
+	rcu_barrier();
 	/*
 	 * sessiond_cleanup() is called when no other thread is running, except
 	 * the ht_cleanup thread, which is needed to destroy the hash tables.