NFSv4: Avoid unnecessary scans of filesystems for delayed delegations

The amount of looping through the list of delegations is occasionally
leading to soft lockups. If the state manager was asked to manage the
delayed return of delegations, then only scan those filesystems
containing delegations that were marked as being delayed.

Fixes: be20037 ("NFSv4: Fix delegation return in cases where we have to retry")
Signed-off-by: Trond Myklebust <[email protected]>

Author: Trond Myklebust

fs/nfs/delegation.c

@@ -331,14 +331,16 @@ nfs_start_delegation_return(struct nfs_inode *nfsi)
 }
 
 static void nfs_abort_delegation_return(struct nfs_delegation *delegation,
-					struct nfs_client *clp, int err)
+					struct nfs_server *server, int err)
 {
-
 	spin_lock(&delegation->lock);
 	clear_bit(NFS_DELEGATION_RETURNING, &delegation->flags);
 	if (err == -EAGAIN) {
 		set_bit(NFS_DELEGATION_RETURN_DELAYED, &delegation->flags);
-		set_bit(NFS4CLNT_DELEGRETURN_DELAYED, &clp->cl_state);
+		set_bit(NFS4SERV_DELEGRETURN_DELAYED,
+			&server->delegation_flags);
+		set_bit(NFS4CLNT_DELEGRETURN_DELAYED,
+			&server->nfs_client->cl_state);
 	}
 	spin_unlock(&delegation->lock);
 }
@@ -548,7 +550,7 @@ int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,
  */
 static int nfs_end_delegation_return(struct inode *inode, struct nfs_delegation *delegation, int issync)
 {
-	struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
+	struct nfs_server *server = NFS_SERVER(inode);
 	unsigned int mode = O_WRONLY | O_RDWR;
 	int err = 0;
 
@@ -570,11 +572,11 @@ static int nfs_end_delegation_return(struct inode *inode, struct nfs_delegation
 		/*
 		 * Guard against state recovery
 		 */
-		err = nfs4_wait_clnt_recover(clp);
+		err = nfs4_wait_clnt_recover(server->nfs_client);
 	}
 
 	if (err) {
-		nfs_abort_delegation_return(delegation, clp, err);
+		nfs_abort_delegation_return(delegation, server, err);
 		goto out;
 	}
 
@@ -678,13 +680,17 @@ static bool nfs_server_clear_delayed_delegations(struct nfs_server *server)
 	struct nfs_delegation *d;
 	bool ret = false;
 
+	if (!test_and_clear_bit(NFS4SERV_DELEGRETURN_DELAYED,
+				&server->delegation_flags))
+		goto out;
 	list_for_each_entry_rcu (d, &server->delegations, super_list) {
 		if (!test_bit(NFS_DELEGATION_RETURN_DELAYED, &d->flags))
 			continue;
 		nfs_mark_return_delegation(server, d);
 		clear_bit(NFS_DELEGATION_RETURN_DELAYED, &d->flags);
 		ret = true;
 	}
+out:
 	return ret;
 }
 

include/linux/nfs_fs_sb.h

@@ -253,6 +253,7 @@ struct nfs_server {
 	unsigned long		delegation_flags;
 #define NFS4SERV_DELEGRETURN		(1)
 #define NFS4SERV_DELEGATION_EXPIRED	(2)
+#define NFS4SERV_DELEGRETURN_DELAYED	(3)
 	unsigned long		delegation_gen;
 	unsigned long		mig_gen;
 	unsigned long		mig_status;