[PATCH 2/2] iov: Fix netfs_extract_user_to_sg()

[David Howells <dhowells@redhat.com>]

Fix the loop check in netfs_extract_user_to_sg() for extraction from
user-backed iterators to do the body if npages > 0, not if npages < 0
(which it can never be).

This isn't currently used by cifs, which only ever extracts data from BVEC,
KVEC and XARRAY iterators at this level, user-backed iterators having being
decanted into BVEC iterators at a higher level to accommodate the work
being done in a kernel thread.

Found by smatch:
	fs/netfs/iterator.c:139 netfs_extract_user_to_sg() warn: unsigned 'npages' is never less than zero.

Fixes: 018584697533 ("netfs: Add a function to extract an iterator into a scatterlist")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: linux-cachefs@redhat.com
Link: https://lore.kernel.org/oe-kbuild-all/202302261115.P3TQi1ZO-lkp@intel.com/
---
 fs/netfs/iterator.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/netfs/iterator.c b/fs/netfs/iterator.c
index f00d43b8ac0a..e9a45dea748a 100644
--- a/fs/netfs/iterator.c
+++ b/fs/netfs/iterator.c
@@ -134,7 +134,7 @@ static ssize_t netfs_extract_user_to_sg(struct iov_iter *iter,
 		npages = DIV_ROUND_UP(off + len, PAGE_SIZE);
 		sg_max -= npages;
 
-		for (; npages < 0; npages--) {
+		for (; npages > 0; npages--) {
 			struct page *page = *pages;
 			size_t seg = min_t(size_t, PAGE_SIZE - off, len);