FAILED: patch "[PATCH] NFS: Fix an Oopsable condition in __nfs_pageio_add_request()" failed to apply to 4.14-stable tree

The patch below does not apply to the 4.14-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 <[email protected]>.

thanks,

greg k-h

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

From 56517ab958b7c11030e626250c00b9b1a24b41eb Mon Sep 17 00:00:00 2001
From: Trond Myklebust <[email protected]>
Date: Tue, 25 May 2021 10:23:05 -0400
Subject: [PATCH] NFS: Fix an Oopsable condition in __nfs_pageio_add_request()

Ensure that nfs_pageio_error_cleanup() resets the mirror array contents, so that the structure reflects the fact that it is now empty. Also change the test in nfs_pageio_do_add_request() to be more robust by checking whether or not the list is empty rather than relying on the value of pg_count.

index 6c20b28d9d7c..d35c84af44e0 100644
@@ -1094,15 +1094,16 @@ nfs_pageio_do_add_request(struct nfs_pageio_descriptor *desc,
 	struct nfs_page *prev = NULL;
 	unsigned int size;
 
-	if (mirror->pg_count != 0) {
-		prev = nfs_list_entry(mirror->pg_list.prev);
-	} else {
+	if (list_empty(&mirror->pg_list)) {
 		if (desc->pg_ops->pg_init)
 			desc->pg_ops->pg_init(desc, req);
 		if (desc->pg_error < 0)
 			return 0;
 		mirror->pg_base = req->wb_pgbase;
-	}
+		mirror->pg_count = 0;
+		mirror->pg_recoalesce = 0;
+	} else
+		prev = nfs_list_entry(mirror->pg_list.prev);
 
 	if (desc->pg_maxretrans && req->wb_nio > desc->pg_maxretrans) {
 		if (NFS_SERVER(desc->pg_inode)->flags & NFS_MOUNT_SOFTERR)