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>

1 files changed, 25 insertions, 14 deletions

diff --git a/fs/lockd/clntlock.c b/fs/lockd/clntlock.c
index bce74446870..52774feab93 100644
--- a/fs/lockd/clntlock.c
+++ b/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);
@@ -164,6 +163,13 @@ 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.
@@ -171,12 +177,10 @@ void nlmclnt_prepare_reclaim(struct nlm_host *host, u32 newstate)
 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) {