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, 13 insertions, 1 deletions

diff --git a/fs/lockd/clntproc.c b/fs/lockd/clntproc.c
index f96e381..4db6209 100644
--- a/fs/lockd/clntproc.c
+++ b/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);