lockd: close potential race with rapid lockd_up/lockd_down cycle

If lockd_down is called very rapidly after lockd_up returns, then
there is a slim chance that lockd() will never be called. kthread()
will return before calling the function, so we'll end up never
actually calling the cleanup functions for the thread.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 2169af4..5bd9bf0 100644 (file)
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -50,7 +50,7 @@ EXPORT_SYMBOL(nlmsvc_ops);
 static DEFINE_MUTEX(nlmsvc_mutex);
 static unsigned int            nlmsvc_users;
 static struct task_struct      *nlmsvc_task;
-static struct svc_serv         *nlmsvc_serv;
+static struct svc_rqst         *nlmsvc_rqst;
 int                            nlmsvc_grace_period;
 unsigned long                  nlmsvc_timeout;
 
@@ -194,20 +194,11 @@ lockd(void *vrqstp)
 
                svc_process(rqstp);
        }
-
        flush_signals(current);
        if (nlmsvc_ops)
                nlmsvc_invalidate_all();
        nlm_shutdown_hosts();
-
        unlock_kernel();
-
-       nlmsvc_task = NULL;
-       nlmsvc_serv = NULL;
-
-       /* Exit the RPC thread */
-       svc_exit_thread(rqstp);
-
        return 0;
 }
 
@@ -254,16 +245,15 @@ int
 lockd_up(int proto) /* Maybe add a 'family' option when IPv6 is supported ?? */
 {
        struct svc_serv *serv;
-       struct svc_rqst *rqstp;
        int             error = 0;
 
        mutex_lock(&nlmsvc_mutex);
        /*
         * Check whether we're already up and running.
         */
-       if (nlmsvc_serv) {
+       if (nlmsvc_rqst) {
                if (proto)
-                       error = make_socks(nlmsvc_serv, proto);
+                       error = make_socks(nlmsvc_rqst->rq_server, proto);
                goto out;
        }
 
@@ -288,9 +278,10 @@ lockd_up(int proto) /* Maybe add a 'family' option when IPv6 is supported ?? */
        /*
         * Create the kernel thread and wait for it to start.
         */
-       rqstp = svc_prepare_thread(serv, &serv->sv_pools[0]);
-       if (IS_ERR(rqstp)) {
-               error = PTR_ERR(rqstp);
+       nlmsvc_rqst = svc_prepare_thread(serv, &serv->sv_pools[0]);
+       if (IS_ERR(nlmsvc_rqst)) {
+               error = PTR_ERR(nlmsvc_rqst);
+               nlmsvc_rqst = NULL;
                printk(KERN_WARNING
                        "lockd_up: svc_rqst allocation failed, error=%d\n",
                        error);
@@ -298,16 +289,15 @@ lockd_up(int proto) /* Maybe add a 'family' option when IPv6 is supported ?? */
        }
 
        svc_sock_update_bufs(serv);
-       nlmsvc_serv = rqstp->rq_server;
 
-       nlmsvc_task = kthread_run(lockd, rqstp, serv->sv_name);
+       nlmsvc_task = kthread_run(lockd, nlmsvc_rqst, serv->sv_name);
        if (IS_ERR(nlmsvc_task)) {
                error = PTR_ERR(nlmsvc_task);
+               svc_exit_thread(nlmsvc_rqst);
                nlmsvc_task = NULL;
-               nlmsvc_serv = NULL;
+               nlmsvc_rqst = NULL;
                printk(KERN_WARNING
                        "lockd_up: kthread_run failed, error=%d\n", error);
-               svc_exit_thread(rqstp);
                goto destroy_and_out;
        }
 
@@ -346,6 +336,9 @@ lockd_down(void)
                BUG();
        }
        kthread_stop(nlmsvc_task);
+       svc_exit_thread(nlmsvc_rqst);
+       nlmsvc_task = NULL;
+       nlmsvc_rqst = NULL;
 out:
        mutex_unlock(&nlmsvc_mutex);
 }