From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Benjamin Marzinski <bmarzins@redhat.com>
Date: Fri, 23 Oct 2020 11:38:24 -0500
Subject: [PATCH] libmultipath: don't dlclose tur checker DSO

The multipathd tur checker thread is designed to be able to finish at
any time, even after the tur checker itself has been freed. The
multipathd shutdown code makes sure all the checkers have been freed
before freeing the checker_class and calling dlclose() to unload the
DSO, but this doesn't guarantee that the checker threads have finished.
If one hasn't, the DSO will get unloaded while the thread still running
code from it, causing a segfault. Unfortunately, it's not possible to be
sure that all tur checker threads have ended during shutdown, without
making them joinable.

However, since libmultipath will never be reinitialized after it has
been uninitialzed, not dlclosing the tur checker DSO once a thread is
started has minimal cost (keeping the DSO code around until the program
exits, which usually happens right after freeing the checkers).

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
---
 libmultipath/checkers.c     | 10 +++++++++-
 libmultipath/checkers.h     |  1 +
 libmultipath/checkers/tur.c |  1 +
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/libmultipath/checkers.c b/libmultipath/checkers.c
index 8d2be8a9..6359e5d8 100644
--- a/libmultipath/checkers.c
+++ b/libmultipath/checkers.c
@@ -21,6 +21,7 @@ struct checker_class {
 	void (*reset)(void);		     /* to reset the global variables */
 	const char **msgtable;
 	short msgtable_size;
+	int keep_dso;
 };
 
 char *checker_state_names[] = {
@@ -69,7 +70,7 @@ void free_checker_class(struct checker_class *c)
 	list_del(&c->node);
 	if (c->reset)
 		c->reset();
-	if (c->handle) {
+	if (c->handle && !c->keep_dso) {
 		if (dlclose(c->handle) != 0) {
 			condlog(0, "Cannot unload checker %s: %s",
 				c->name, dlerror());
@@ -192,6 +193,13 @@ out:
 	return NULL;
 }
 
+void checker_keep_dso(struct checker * c)
+{
+	if (!c || !c->cls)
+		return;
+	c->cls->keep_dso = 1;
+}
+
 void checker_set_fd (struct checker * c, int fd)
 {
 	if (!c)
diff --git a/libmultipath/checkers.h b/libmultipath/checkers.h
index b458118d..f183cff9 100644
--- a/libmultipath/checkers.h
+++ b/libmultipath/checkers.h
@@ -145,6 +145,7 @@ void checker_reset (struct checker *);
 void checker_set_sync (struct checker *);
 void checker_set_async (struct checker *);
 void checker_set_fd (struct checker *, int);
+void checker_keep_dso(struct checker *c);
 void checker_enable (struct checker *);
 void checker_disable (struct checker *);
 int checker_check (struct checker *, int);
diff --git a/libmultipath/checkers/tur.c b/libmultipath/checkers/tur.c
index e886fcf8..fd58d62a 100644
--- a/libmultipath/checkers/tur.c
+++ b/libmultipath/checkers/tur.c
@@ -394,6 +394,7 @@ int libcheck_check(struct checker * c)
 		uatomic_set(&ct->running, 1);
 		tur_set_async_timeout(c);
 		setup_thread_attr(&attr, 32 * 1024, 1);
+		checker_keep_dso(c);
 		r = pthread_create(&ct->thread, &attr, tur_thread, ct);
 		pthread_attr_destroy(&attr);
 		if (r) {
-- 
2.17.2