fs: dlm: fix race in nodeid2con (4f2b30fd) · Commits · 戴 / test

This patch fixes a race in nodeid2con in cases that we parallel running a lookup and both will create a connection structure for the same nodeid. It's a rare case to create a new connection structure to keep reader lockless we just do a lookup inside the protection area again and drop previous work if this race happens. Fixes: ("fs: dlm: make connection hash lockless") Signed-off-by:

Alexander Aring <aahringo@redhat.com> Signed-off-by:

David Teigland <teigland@redhat.com>

fs/dlm/lowcomms.c

+15 −1

Original line number	Diff line number	Diff line
		@@ -175,7 +175,7 @@ static struct connection *__find_con(int nodeid)
		*/
		static struct connection *nodeid2con(int nodeid, gfp_t alloc)
		{
		struct connection *con = NULL;
		struct connection con, tmp;
		int r;

		con = __find_con(nodeid);
		@@ -213,6 +213,20 @@ static struct connection *nodeid2con(int nodeid, gfp_t alloc)
		r = nodeid_hash(nodeid);

		spin_lock(&connections_lock);
		/* Because multiple workqueues/threads calls this function it can
		* race on multiple cpu's. Instead of locking hot path __find_con()
		* we just check in rare cases of recently added nodes again
		* under protection of connections_lock. If this is the case we
		* abort our connection creation and return the existing connection.
		*/
		tmp = __find_con(nodeid);
		if (tmp) {
		spin_unlock(&connections_lock);
		kfree(con->rx_buf);
		kfree(con);
		return tmp;
		}

		hlist_add_head_rcu(&con->list, &connection_hash[r]);
		spin_unlock(&connections_lock);

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