[PATCH] NFS: fix an infinite request retry in an off-by-one last page read

[Dan Aloni <dan.aloni@vastdata.com>]

Due to change 8cfb9015280d ("NFS: Always provide aligned buffers to the
RPC read layers"), a read of 0xfff is aligned up to server rsize of
0x1000.

As a result, in a test where the server has a file of size
0x7fffffffffffffff, and the client tries to read from the offset
0x7ffffffffffff000, the read causes loff_t overflow in the server and it
returns an NFS code of EINVAL to the client. The client as a result
indefinitely retries the request.

This fixes the issue by cancelling the alignment for that case.

Fixes: 8cfb9015280d ("NFS: Always provide aligned buffers to the RPC read layers")
Signed-off-by: Dan Aloni <dan.aloni@vastdata.com>
---
 fs/nfs/read.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index 08d6cc57cbc3..d6fac5e4d3f4 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -296,16 +296,19 @@ readpage_async_filler(void *data, struct page *page)
 	struct inode *inode = page_file_mapping(page)->host;
 	unsigned int rsize = NFS_SERVER(inode)->rsize;
 	struct nfs_page *new;
-	unsigned int len, aligned_len;
+	unsigned int len, request_len;
 	int error;
 
 	len = nfs_page_length(page);
 	if (len == 0)
 		return nfs_return_empty_page(page);
 
-	aligned_len = min_t(unsigned int, ALIGN(len, rsize), PAGE_SIZE);
+	if (likely(page_index(page) != (LLONG_MAX >> PAGE_SHIFT)))
+		request_len = min_t(unsigned int, ALIGN(len, rsize), PAGE_SIZE);
+	else
+		request_len = len;
 
-	new = nfs_create_request(desc->ctx, page, 0, aligned_len);
+	new = nfs_create_request(desc->ctx, page, 0, request_len);
 	if (IS_ERR(new))
 		goto out_error;
 
-- 
2.23.0