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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: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
Scott Mayhew 2017-12-05 13:55:44 -05:00 committed by Anna Schumaker
parent eb5b46faa6
commit c156618e15
2 changed files with 24 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
fs/nfs/client.c
View File

@ -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;

17
fs/nfs/nfs4client.c
View File

@ -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;