[dm-devel] [PATCH v3 02/29] multipathd: Fix liburcu memory leak

[mwilck at suse.com]

From: Martin Wilck <mwilck at suse.com>

Fix this leak in multipathd, reported by valgrind, that messes up
multipathd's otherwise clean leak report:

==23823== 336 bytes in 1 blocks are possibly lost in loss record 3 of 3
==23823==    at 0x483AB65: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==23823==    by 0x4012F16: _dl_allocate_tls (in /lib64/ld-2.31.so)
==23823==    by 0x493BB8E: pthread_create@@GLIBC_2.2.5 (in /lib64/libpthread-2.31.so)
==23823==    by 0x492A9A9: call_rcu_data_init (urcu-call-rcu-impl.h:437)
==23823==    by 0x492AD2F: UnknownInlinedFun (urcu-call-rcu-impl.h:492)
==23823==    by 0x492AD2F: create_call_rcu_data_memb (urcu-call-rcu-impl.h:504)
==23823==    by 0x1164E3: child.constprop.0.isra.0 (main.c:2915)
==23823==    by 0x10F50C: main (main.c:3335)
==23823==
==23823== LEAK SUMMARY:
==23823==    definitely lost: 0 bytes in 0 blocks
==23823==    indirectly lost: 0 bytes in 0 blocks
==23823==      possibly lost: 336 bytes in 1 blocks

The problem is caused by using liburcu's default RCU call handler,
which liburcu refuses to stop/join. See comments in the code.

Signed-off-by: Martin Wilck <mwilck at suse.com>
---
 multipathd/main.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/multipathd/main.c b/multipathd/main.c
index c5c374b..ce14bb6 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -2889,6 +2889,48 @@ set_oom_adj (void)
 	condlog(0, "couldn't adjust oom score");
 }
 
+/*
+ * Use a non-default call_rcu_data for child().
+ *
+ * We do this to avoid a memory leak from liburcu.
+ * liburcu never frees the default rcu handler (see comments on
+ * call_rcu_data_free() in urcu-call-rcu-impl.h), its thread
+ * can't be joined with pthread_join(), leaving a memory leak.
+ *
+ * Therefore we create our own, which can be destroyed and joined.
+ */
+static struct call_rcu_data *setup_rcu(void)
+{
+	struct call_rcu_data *crdp;
+
+	rcu_init();
+	rcu_register_thread();
+	crdp = create_call_rcu_data(0UL, -1);
+	if (crdp != NULL)
+		set_thread_call_rcu_data(crdp);
+	return crdp;
+}
+
+static struct call_rcu_data *mp_rcu_data;
+
+static void cleanup_rcu(void)
+{
+	pthread_t rcu_thread;
+
+	/* Wait for any pending RCU calls */
+	rcu_barrier();
+	if (mp_rcu_data != NULL) {
+		rcu_thread = get_call_rcu_thread(mp_rcu_data);
+		/* detach this thread from the RCU thread */
+		set_thread_call_rcu_data(NULL);
+		synchronize_rcu();
+		/* tell RCU thread to exit */
+		call_rcu_data_free(mp_rcu_data);
+		pthread_join(rcu_thread, NULL);
+	}
+	rcu_unregister_thread();
+}
+
 static int
 child (__attribute__((unused)) void *param)
 {
@@ -2906,7 +2948,8 @@ child (__attribute__((unused)) void *param)
 
 	mlockall(MCL_CURRENT | MCL_FUTURE);
 	signal_init();
-	rcu_init();
+	mp_rcu_data = setup_rcu();
+	atexit(cleanup_rcu);
 
 	setup_thread_attr(&misc_attr, 64 * 1024, 0);
 	setup_thread_attr(&uevent_attr, DEFAULT_UEVENT_STACKSIZE * 1024, 0);
-- 
2.29.0