FAILED: patch "[PATCH] NFS: nfs_delegation_find_inode_server must first reference" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 113aac6d567bda783af36d08f73bfda47d8e9a40 Mon Sep 17 00:00:00 2001
From: Trond Myklebust <trond.myklebust@hammerspace.com>
Date: Sun, 10 Jan 2021 15:46:06 -0500
Subject: [PATCH] NFS: nfs_delegation_find_inode_server must first reference
 the superblock

Before referencing the inode, we must ensure that the superblock can be
referenced. Otherwise, we can end up with iput() calling superblock
operations that are no longer valid or accessible.

Fixes: e39d8a186ed0 ("NFSv4: Fix an Oops during delegation callbacks")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 816e1427f17e..04bf8066980c 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -1011,22 +1011,24 @@ nfs_delegation_find_inode_server(struct nfs_server *server,
 				 const struct nfs_fh *fhandle)
 {
 	struct nfs_delegation *delegation;
-	struct inode *freeme, *res = NULL;
+	struct super_block *freeme = NULL;
+	struct inode *res = NULL;
 
 	list_for_each_entry_rcu(delegation, &server->delegations, super_list) {
 		spin_lock(&delegation->lock);
 		if (delegation->inode != NULL &&
 		    !test_bit(NFS_DELEGATION_REVOKED, &delegation->flags) &&
 		    nfs_compare_fh(fhandle, &NFS_I(delegation->inode)->fh) == 0) {
-			freeme = igrab(delegation->inode);
-			if (freeme && nfs_sb_active(freeme->i_sb))
-				res = freeme;
+			if (nfs_sb_active(server->super)) {
+				freeme = server->super;
+				res = igrab(delegation->inode);
+			}
 			spin_unlock(&delegation->lock);
 			if (res != NULL)
 				return res;
 			if (freeme) {
 				rcu_read_unlock();
-				iput(freeme);
+				nfs_sb_deactive(freeme);
 				rcu_read_lock();
 			}
 			return ERR_PTR(-EAGAIN);