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Commit c156618e authored by Scott Mayhew's avatar Scott Mayhew Committed by Anna Schumaker
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nfs: fix a deadlock in nfs client initialization 



The following deadlock can occur between a process waiting for a client
to initialize in while walking the client list during nfsv4 server trunking
detection and another process waiting for the nfs_clid_init_mutex so it
can initialize that client:

Process 1                               Process 2
---------                               ---------
spin_lock(&nn->nfs_client_lock);
list_add_tail(&CLIENTA->cl_share_link,
        &nn->nfs_client_list);
spin_unlock(&nn->nfs_client_lock);
                                        spin_lock(&nn->nfs_client_lock);
                                        list_add_tail(&CLIENTB->cl_share_link,
                                                &nn->nfs_client_list);
                                        spin_unlock(&nn->nfs_client_lock);
                                        mutex_lock(&nfs_clid_init_mutex);
                                        nfs41_walk_client_list(clp, result, cred);
                                        nfs_wait_client_init_complete(CLIENTA);
(waiting for nfs_clid_init_mutex)

Make sure nfs_match_client() only evaluates clients that have completed
initialization in order to prevent that deadlock.

This patch also fixes v4.0 trunking behavior by not marking the client
NFS_CS_READY until the clientid has been confirmed.

Signed-off-by: default avatarScott Mayhew <smayhew@redhat.com>
Signed-off-by: default avatarAnna Schumaker <Anna.Schumaker@Netapp.com>
parent eb5b46fa

fs/nfs/client.c

+11 −0
Original line number Diff line number Diff line
@@ -291,12 +291,23 @@ static struct nfs_client *nfs_match_client(const struct nfs_client_initdata *dat 
	const struct sockaddr *sap = data->addr;

	struct nfs_net *nn = net_generic(data->net, nfs_net_id);



again:

	list_for_each_entry(clp, &nn->nfs_client_list, cl_share_link) {

	        const struct sockaddr *clap = (struct sockaddr *)&clp->cl_addr;

		/* Don't match clients that failed to initialise properly */

		if (clp->cl_cons_state < 0)

			continue;



		/* If a client is still initializing then we need to wait */

		if (clp->cl_cons_state > NFS_CS_READY) {

			refcount_inc(&clp->cl_count);

			spin_unlock(&nn->nfs_client_lock);

			nfs_wait_client_init_complete(clp);

			nfs_put_client(clp);

			spin_lock(&nn->nfs_client_lock);

			goto again;

		}



		/* Different NFS versions cannot share the same nfs_client */

		if (clp->rpc_ops != data->nfs_mod->rpc_ops)

			continue;

fs/nfs/nfs4client.c

+13 −4
Original line number Diff line number Diff line
@@ -404,15 +404,19 @@ struct nfs_client *nfs4_init_client(struct nfs_client *clp, 
	if (error < 0)

		goto error;



	if (!nfs4_has_session(clp))

		nfs_mark_client_ready(clp, NFS_CS_READY);



	error = nfs4_discover_server_trunking(clp, &old);

	if (error < 0)

		goto error;



	if (clp != old)

	if (clp != old) {

		clp->cl_preserve_clid = true;

		/*

		 * Mark the client as having failed initialization so other

		 * processes walking the nfs_client_list in nfs_match_client()

		 * won't try to use it.

		 */

		nfs_mark_client_ready(clp, -EPERM);

	}

	nfs_put_client(clp);

	clear_bit(NFS_CS_TSM_POSSIBLE, &clp->cl_flags);

	return old;
@@ -539,6 +543,9 @@ int nfs40_walk_client_list(struct nfs_client *new, 
	spin_lock(&nn->nfs_client_lock);

	list_for_each_entry(pos, &nn->nfs_client_list, cl_share_link) {



		if (pos == new)

			goto found;



		status = nfs4_match_client(pos, new, &prev, nn);

		if (status < 0)

			goto out_unlock;
@@ -559,6 +566,7 @@ int nfs40_walk_client_list(struct nfs_client *new, 
		 * way that a SETCLIENTID_CONFIRM to pos can succeed is

		 * if new and pos point to the same server:

		 */

found:

		refcount_inc(&pos->cl_count);

		spin_unlock(&nn->nfs_client_lock);
@@ -572,6 +580,7 @@ int nfs40_walk_client_list(struct nfs_client *new, 
		case 0:

			nfs4_swap_callback_idents(pos, new);

			pos->cl_confirm = new->cl_confirm;

			nfs_mark_client_ready(pos, NFS_CS_READY);



			prev = NULL;

			*result = pos;