drbd: swap bvec_set_page len and offset

bvec_set_page has the following signature:

static inline void bvec_set_page(struct bio_vec *bv, struct page *page,
		unsigned int len, unsigned int offset)

However, the usage in DRBD swaps the len and offset parameters. This
leads to a bvec with length=0 instead of the intended length=4096, which
causes sock_sendmsg to return -EIO.

This leaves DRBD unable to transmit any pages and thus completely
broken.

Swapping the parameters fixes the regression.

Fixes: eeac740 ("drbd: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()")
Reported-by: Serguei Ivantsov <[email protected]>
Link: https://lore.kernel.org/regressions/CAKH+VT3YLmAn0Y8=q37UTDShqxDLsqPcQ4hBMzY7HPn7zNx+RQ@mail.gmail.com/
Cc: [email protected]
Signed-off-by: Christoph Böhmwalder <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: chrboe

drivers/block/drbd/drbd_main.c

@@ -1557,7 +1557,7 @@ static int _drbd_send_page(struct drbd_peer_device *peer_device, struct page *pa
 	do {
 		int sent;
 
-		bvec_set_page(&bvec, page, offset, len);
+		bvec_set_page(&bvec, page, len, offset);
 		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, len);
 
 		sent = sock_sendmsg(socket, &msg);