NLM: Fix reclaim races

Currently it is possible for a task to remove its locks at the same time as
the NLM recovery thread is trying to recover them. This quickly leads to an
Oops.
Protect the locks using an rw semaphore while they are being recovered.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/lockd/clntlock.c

@@ -147,11 +147,10 @@ u32 nlmclnt_grant(const struct sockaddr_in *addr, const struct nlm_lock *lock)
  * Someone has sent us an SM_NOTIFY. Ensure we bind to the new port number,
  * that we mark locks for reclaiming, and that we bump the pseudo NSM state.
  */
-static inline
-void nlmclnt_prepare_reclaim(struct nlm_host *host, u32 newstate)
+static void nlmclnt_prepare_reclaim(struct nlm_host *host)
 {
+	down_write(&host->h_rwsem);
 	host->h_monitored = 0;
-	host->h_nsmstate = newstate;
 	host->h_state++;
 	host->h_nextrebind = 0;
 	nlm_rebind_host(host);
@@ -164,19 +163,24 @@ void nlmclnt_prepare_reclaim(struct nlm_host *host, u32 newstate)
 	dprintk("NLM: reclaiming locks for host %s", host->h_name);
 }
 
+static void nlmclnt_finish_reclaim(struct nlm_host *host)
+{
+	host->h_reclaiming = 0;
+	up_write(&host->h_rwsem);
+	dprintk("NLM: done reclaiming locks for host %s", host->h_name);
+}
+
 /*
  * Reclaim all locks on server host. We do this by spawning a separate
  * reclaimer thread.
  */
 void
 nlmclnt_recovery(struct nlm_host *host, u32 newstate)
 {
-	if (host->h_reclaiming++) {
-		if (host->h_nsmstate == newstate)
-			return;
-		nlmclnt_prepare_reclaim(host, newstate);
-	} else {
-		nlmclnt_prepare_reclaim(host, newstate);
+	if (host->h_nsmstate == newstate)
+		return;
+	host->h_nsmstate = newstate;
+	if (!host->h_reclaiming++) {
 		nlm_get_host(host);
 		__module_get(THIS_MODULE);
 		if (kernel_thread(reclaimer, host, CLONE_KERNEL) < 0)
@@ -190,6 +194,7 @@ reclaimer(void *ptr)
 	struct nlm_host	  *host = (struct nlm_host *) ptr;
 	struct nlm_wait	  *block;
 	struct file_lock *fl, *next;
+	u32 nsmstate;
 
 	daemonize("%s-reclaim", host->h_name);
 	allow_signal(SIGKILL);
@@ -199,19 +204,25 @@ reclaimer(void *ptr)
 	lock_kernel();
 	lockd_up();
 
+	nlmclnt_prepare_reclaim(host);
 	/* First, reclaim all locks that have been marked. */
 restart:
+	nsmstate = host->h_nsmstate;
 	list_for_each_entry_safe(fl, next, &host->h_reclaim, fl_u.nfs_fl.list) {
 		list_del_init(&fl->fl_u.nfs_fl.list);
 
 		if (signalled())
 			continue;
-		if (nlmclnt_reclaim(host, fl) == 0)
-			list_add_tail(&fl->fl_u.nfs_fl.list, &host->h_granted);
-		goto restart;
+		if (nlmclnt_reclaim(host, fl) != 0)
+			continue;
+		list_add_tail(&fl->fl_u.nfs_fl.list, &host->h_granted);
+		if (host->h_nsmstate != nsmstate) {
+			/* Argh! The server rebooted again! */
+			list_splice_init(&host->h_granted, &host->h_reclaim);
+			goto restart;
+		}
 	}
-
-	host->h_reclaiming = 0;
+	nlmclnt_finish_reclaim(host);
 
 	/* Now, wake up all processes that sleep on a blocked lock */
 	list_for_each_entry(block, &nlm_blocked, b_list) {

fs/lockd/clntproc.c

@@ -508,7 +508,10 @@ nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
 	}
 
 	block = nlmclnt_prepare_block(host, fl);
+again:
 	for(;;) {
+		/* Reboot protection */
+		fl->fl_u.nfs_fl.state = host->h_state;
 		status = nlmclnt_call(req, NLMPROC_LOCK);
 		if (status < 0)
 			goto out_unblock;
@@ -531,10 +534,16 @@ nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
 	}
 
 	if (resp->status == NLM_LCK_GRANTED) {
-		fl->fl_u.nfs_fl.state = host->h_state;
+		down_read(&host->h_rwsem);
+		/* Check whether or not the server has rebooted */
+		if (fl->fl_u.nfs_fl.state != host->h_state) {
+			up_read(&host->h_rwsem);
+			goto again;
+		}
 		fl->fl_flags |= FL_SLEEP;
 		/* Ensure the resulting lock will get added to granted list */
 		do_vfs_lock(fl);
+		up_read(&host->h_rwsem);
 	}
 	status = nlm_stat_to_errno(resp->status);
 out_unblock:
@@ -596,6 +605,7 @@ nlmclnt_reclaim(struct nlm_host *host, struct file_lock *fl)
 static int
 nlmclnt_unlock(struct nlm_rqst *req, struct file_lock *fl)
 {
+	struct nlm_host	*host = req->a_host;
 	struct nlm_res	*resp = &req->a_res;
 	int		status;
 
@@ -604,7 +614,9 @@ nlmclnt_unlock(struct nlm_rqst *req, struct file_lock *fl)
 	 * request, or to deny it with NLM_LCK_DENIED_GRACE_PERIOD. In either
 	 * case, we want to unlock.
 	 */
+	down_read(&host->h_rwsem);
 	do_vfs_lock(fl);
+	up_read(&host->h_rwsem);
 
 	if (req->a_flags & RPC_TASK_ASYNC)
 		return nlm_async_call(req, NLMPROC_UNLOCK, &nlmclnt_unlock_ops);

fs/lockd/host.c

@@ -117,6 +117,7 @@ nlm_lookup_host(int server, struct sockaddr_in *sin,
 	host->h_expires    = jiffies + NLM_HOST_EXPIRE;
 	atomic_set(&host->h_count, 1);
 	init_waitqueue_head(&host->h_gracewait);
+	init_rwsem(&host->h_rwsem);
 	host->h_state      = 0;			/* pseudo NSM state */
 	host->h_nsmstate   = 0;			/* real NSM state */
 	host->h_server	   = server;

include/linux/lockd/lockd.h

@@ -50,6 +50,7 @@ struct nlm_host {
 				h_killed     : 1,
 				h_monitored  : 1;
 	wait_queue_head_t	h_gracewait;	/* wait while reclaiming */
+	struct rw_semaphore	h_rwsem;	/* Reboot recovery lock */
 	u32			h_state;	/* pseudo-state counter */
 	u32			h_nsmstate;	/* true remote NSM state */
 	u32			h_pidcount;	/* Pseudopids */