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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, David Windsor <dwindsor@redhat.com>,
        David Teigland <teigland@redhat.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 079/113] dlm: check if workqueues are NULL before flushing/destroying
Date:   Mon, 29 Jul 2019 21:22:46 +0200
Message-Id: <20190729190714.519242769@linuxfoundation.org>
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[ Upstream commit b355516f450703c9015316e429b66a93dfff0e6f ]

If the DLM lowcomms stack is shut down before any DLM
traffic can be generated, flush_workqueue() and
destroy_workqueue() can be called on empty send and/or recv
workqueues.

Insert guard conditionals to only call flush_workqueue()
and destroy_workqueue() on workqueues that are not NULL.

Signed-off-by: David Windsor <dwindsor@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/dlm/lowcomms.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
index a5e4a221435c..a93ebffe84b3 100644
--- a/fs/dlm/lowcomms.c
+++ b/fs/dlm/lowcomms.c
@@ -1630,8 +1630,10 @@ static void clean_writequeues(void)
 
 static void work_stop(void)
 {
-	destroy_workqueue(recv_workqueue);
-	destroy_workqueue(send_workqueue);
+	if (recv_workqueue)
+		destroy_workqueue(recv_workqueue);
+	if (send_workqueue)
+		destroy_workqueue(send_workqueue);
 }
 
 static int work_start(void)
@@ -1691,13 +1693,17 @@ static void work_flush(void)
 	struct hlist_node *n;
 	struct connection *con;
 
-	flush_workqueue(recv_workqueue);
-	flush_workqueue(send_workqueue);
+	if (recv_workqueue)
+		flush_workqueue(recv_workqueue);
+	if (send_workqueue)
+		flush_workqueue(send_workqueue);
 	do {
 		ok = 1;
 		foreach_conn(stop_conn);
-		flush_workqueue(recv_workqueue);
-		flush_workqueue(send_workqueue);
+		if (recv_workqueue)
+			flush_workqueue(recv_workqueue);
+		if (send_workqueue)
+			flush_workqueue(send_workqueue);
 		for (i = 0; i < CONN_HASH_SIZE && ok; i++) {
 			hlist_for_each_entry_safe(con, n,
 						  &connection_hash[i], list) {
-- 
2.20.1