[RFC PATCH 06/37] copy_page_to_iter(): fix ITER_DISCARD case

[Al Viro]

we need to advance the iterator...

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
 lib/iov_iter.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 12fb04b23143..c8877cffb7bc 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -965,9 +965,12 @@ static size_t __copy_page_to_iter(struct page *page, size_t offset, size_t bytes
 		size_t wanted = copy_to_iter(kaddr + offset, bytes, i);
 		kunmap_atomic(kaddr);
 		return wanted;
-	} else if (unlikely(iov_iter_is_discard(i)))
+	} else if (unlikely(iov_iter_is_discard(i))) {
+		if (unlikely(i->count < bytes))
+			bytes = i->count;
+		i->count -= bytes;
 		return bytes;
-	else if (likely(!iov_iter_is_pipe(i)))
+	} else if (likely(!iov_iter_is_pipe(i)))
 		return copy_page_to_iter_iovec(page, offset, bytes, i);
 	else
 		return copy_page_to_iter_pipe(page, offset, bytes, i);
-- 
2.11.0