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 stable@vger.kernel.org.

thanks,

greg k-h

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

From 56517ab958b7c11030e626250c00b9b1a24b41eb Mon Sep 17 00:00:00 2001

From: Trond Myklebust trond.myklebust@hammerspace.com 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.

Fixes: a7d42ddb3099 ("nfs: add mirroring support to pgio layer") Signed-off-by: Trond Myklebust trond.myklebust@hammerspace.com

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c index 6c20b28d9d7c..d35c84af44e0 100644 --- a/fs/nfs/pagelist.c +++ b/fs/nfs/pagelist.c @@ -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)