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>

1 files changed, 13 insertions, 20 deletions

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 2169af4d5455..5bd9bf0fa9df 100644
--- 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);
 }