Commit 8e60029f authored Feb 11, 2008 by Jeff Layton Committed by Trond Myklebust Feb 13, 2008

NFS: fix reference counting for NFSv4 callback thread

The reference counting for the NFSv4 callback thread stays artificially
high. When this thread comes down, it doesn't properly tear down the
svc_serv, causing a memory leak. In my testing on an older kernel on
x86_64, memory would leak out of the 8k kmalloc slab. So, we're leaking
at least a page of memory every time the thread comes down.

svc_create() creates the svc_serv with a sv_nrthreads count of 1, and
then svc_create_thread() increments that count. Whenever the callback
thread is started it has a sv_nrthreads count of 2. When coming down, it
calls svc_exit_thread() which decrements that count and if it hits 0, it
tears everything down. That never happens here since the count is always
at 2 when the thread exits.

The problem is that nfs_callback_up() should be calling svc_destroy() on
the svc_serv on both success and failure. This is how lockd_up_proto()
handles the reference counting, and doing that here fixes the leak.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

parent e760e716

fs/nfs/callback.c

+12 −6

Original line number	Diff line number	Diff line
		@@ -105,7 +105,7 @@ static void nfs_callback_svc(struct svc_rqst *rqstp)
		*/
		int nfs_callback_up(void)
		{
		struct svc_serv *serv;
		struct svc_serv *serv = NULL;
		int ret = 0;

		lock_kernel();
		@@ -122,24 +122,30 @@ int nfs_callback_up(void)
		ret = svc_create_xprt(serv, "tcp", nfs_callback_set_tcpport,
		SVC_SOCK_ANONYMOUS);
		if (ret <= 0)
		goto out_destroy;
		goto out_err;
		nfs_callback_tcpport = ret;
		dprintk("Callback port = 0x%x\n", nfs_callback_tcpport);

		ret = svc_create_thread(nfs_callback_svc, serv);
		if (ret < 0)
		goto out_destroy;
		goto out_err;
		nfs_callback_info.serv = serv;
		wait_for_completion(&nfs_callback_info.started);
		out:
		/*
		* svc_create creates the svc_serv with sv_nrthreads == 1, and then
		* svc_create_thread increments that. So we need to call svc_destroy
		* on both success and failure so that the refcount is 1 when the
		* thread exits.
		*/
		if (serv)
		svc_destroy(serv);
		mutex_unlock(&nfs_callback_mutex);
		unlock_kernel();
		return ret;
		out_destroy:
		out_err:
		dprintk("Couldn't create callback socket or server thread; err = %d\n",
		ret);
		svc_destroy(serv);
		out_err:
		nfs_callback_info.users--;
		goto out;
		}