[PATCH 4/4] NFSv4: Avoid unnecessary scans of filesystems for delayed delegations

[trondmy@xxxxxxxxxx]

From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>

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: be20037725d1 ("NFSv4: Fix delegation return in cases where we have to retry")
Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
---
 fs/nfs/delegation.c       | 18 ++++++++++++------
 include/linux/nfs_fs_sb.h |  1 +
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index abd952cc47e4..325ba0663a6d 100644
--- a/fs/nfs/delegation.c
+++ b/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;
 	}
 
@@ -678,6 +680,9 @@ 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;
@@ -685,6 +690,7 @@ static bool nfs_server_clear_delayed_delegations(struct nfs_server *server)
 		clear_bit(NFS_DELEGATION_RETURN_DELAYED, &d->flags);
 		ret = true;
 	}
+out:
 	return ret;
 }
 
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 7d6f164036fa..108862d81b57 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/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;
-- 
2.48.1