Patch "tipc: fix nametbl_lock soft lockup at module exit" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

tipc: fix nametbl_lock soft lockup at module exit

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tipc-fix-nametbl_lock-soft-lockup-at-module-exit.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Parthasarathy Bhuvaragan <[email protected]>
Date: Tue, 24 Jan 2017 13:00:46 +0100
Subject: tipc: fix nametbl_lock soft lockup at module exit

From: Parthasarathy Bhuvaragan <[email protected]>

[ Upstream commit 9dc3abdd1f7ea524e8552e0a3ef01219892ed1f4 ]

Commit 333f796235a527 ("tipc: fix a race condition leading to subscriber refcnt bug") reveals a soft lockup while acquiring nametbl_lock.

Before commit 333f796235a527, we call tipc_conn_shutdown() from tipc_close_conn() in the context of tipc_topsrv_stop(). In that context, we are allowed to grab the nametbl_lock.

Commit 333f796235a527, moved tipc_conn_release (renamed from tipc_conn_shutdown) to the connection refcount cleanup. This allows either tipc_nametbl_withdraw() or tipc_topsrv_stop() to the cleanup.

Since tipc_exit_net() first calls tipc_topsrv_stop() and then tipc_nametble_withdraw() increases the chances for the later to perform the connection cleanup.

The soft lockup occurs in the call chain of tipc_nametbl_withdraw(), when it performs the tipc_conn_kref_release() as it tries to grab nametbl_lock again while holding it already. tipc_nametbl_withdraw() grabs nametbl_lock
tipc_nametbl_remove_publ()
tipc_subscrp_report_overlap()
tipc_subscrp_send_event()
tipc_conn_sendmsg()
<< if (con->flags != CF_CONNECTED) we do conn_put(),
triggering the cleanup as refcount=0. >>
tipc_conn_kref_release
tipc_sock_release
tipc_conn_release
tipc_subscrb_delete
tipc_subscrp_delete
tipc_nametbl_unsubscribe << Soft Lockup >>

The previous changes in this series fixes the race conditions fixed by commit 333f796235a527. Hence we can now revert the commit.

---
 net/tipc/server.c |   16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

@@ -86,7 +86,6 @@ struct outqueue_entry {
 static void tipc_recv_work(struct work_struct *work);
 static void tipc_send_work(struct work_struct *work);
 static void tipc_clean_outqueues(struct tipc_conn *con);
-static void tipc_sock_release(struct tipc_conn *con);
 
 static void tipc_conn_kref_release(struct kref *kref)
 {

@@ -104,7 +103,6 @@ static void tipc_conn_kref_release(struc
 		}
 		saddr->scope = -TIPC_NODE_SCOPE;
 		kernel_bind(sock, (struct sockaddr *)saddr, sizeof(*saddr));
-		tipc_sock_release(con);
 		sock_release(sock);
 		con->sock = NULL;
 

@@ -194,19 +192,15 @@ static void tipc_unregister_callbacks(st
 	write_unlock_bh(&sk->sk_callback_lock);
 }
 
-static void tipc_sock_release(struct tipc_conn *con)
+static void tipc_close_conn(struct tipc_conn *con)
 {
 	struct tipc_server *s = con->server;
 
-	if (con->conid)
-		s->tipc_conn_release(con->conid, con->usr_data);
-
-	tipc_unregister_callbacks(con);
-}
-
-static void tipc_close_conn(struct tipc_conn *con)
-{
 	if (test_and_clear_bit(CF_CONNECTED, &con->flags)) {
+		tipc_unregister_callbacks(con);
+
+		if (con->conid)
+			s->tipc_conn_release(con->conid, con->usr_data);
 
 		/* We shouldn't flush pending works as we may be in the
 		 * thread. In fact the races with pending rx/tx work structs

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/tipc-fix-nametbl_lock-soft-lockup-at-module-exit.patch queue-4.9/tipc-fix-cleanup-at-module-unload.patch