cifs: drop the incorrect assertion in cifs_swap_rw()

Since commit 2282679 ("mm: submit multipage write for SWP_FS_OPS
swap-space"), we can plug multiple pages then unplug them all together.
That means iov_iter_count(iter) could be way bigger than PAGE_SIZE, it
actually equals the size of iov_iter_npages(iter, INT_MAX).

Note this issue has nothing to do with large folios as we don't support
THP_SWPOUT to non-block devices.

Fixes: 2282679 ("mm: submit multipage write for SWP_FS_OPS swap-space")
Reported-by: Christoph Hellwig <[email protected]>
Closes: https://lore.kernel.org/linux-mm/[email protected]/
Cc: NeilBrown <[email protected]>
Cc: Anna Schumaker <[email protected]>
Cc: Steve French <[email protected]>
Cc: Trond Myklebust <[email protected]>
Cc: Chuanhua Han <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Chris Li <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Jeff Layton <[email protected]>
Cc: Paulo Alcantara <[email protected]>
Cc: Ronnie Sahlberg <[email protected]>
Cc: Shyam Prasad N <[email protected]>
Cc: Tom Talpey <[email protected]>
Cc: Bharath SM <[email protected]>
Cc: <[email protected]>
Signed-off-by: Barry Song <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: Barry Song

fs/smb/client/file.c

@@ -3200,8 +3200,6 @@ static int cifs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
 {
 	ssize_t ret;
 
-	WARN_ON_ONCE(iov_iter_count(iter) != PAGE_SIZE);
-
 	if (iov_iter_rw(iter) == READ)
 		ret = netfs_unbuffered_read_iter_locked(iocb, iter);
 	else