libceph: Partially revert changes to support MSG_SPLICE_PAGES

Fix the mishandling of MSG_DONTWAIT and also reinstates the per-page
checking of the source pages (which might have come from a DIO write by
userspace) by partially reverting the changes to support MSG_SPLICE_PAGES
and doing things a little differently. In messenger_v1:

(1) The ceph_tcp_sendpage() is resurrected and the callers reverted to use
that.

(2) The callers now pass MSG_MORE unconditionally. Previously, they were
passing in MSG_MORE|MSG_SENDPAGE_NOTLAST and then degrading that to
just MSG_MORE on the last call to ->sendpage().

(3) Make ceph_tcp_sendpage() a wrapper around sendmsg() rather than
sendpage(), setting MSG_SPLICE_PAGES if sendpage_ok() returns true on
the page.

In messenger_v2:

(4) Bring back do_try_sendpage() and make the callers use that.

(5) Make do_try_sendpage() use sendmsg() for both cases and set
MSG_SPLICE_PAGES if sendpage_ok() is set.

Fixes: 40a8c17aa770 ("ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage")
Fixes: fa094ccae1e7 ("ceph: Use sendmsg(MSG_SPLICE_PAGES) rather than sendpage()")
Reported-by: Ilya Dryomov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]/
Link: https://lore.kernel.org/r/[e-mail]/
Signed-off-by: David Howells <[e-mail]>
cc: Xiubo Li <[e-mail]>
cc: Jeff Layton <[e-mail]>
cc: Jens Axboe <[e-mail]>
cc: Matthew Wilcox <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]/ # v1
Link: https://lore.kernel.org/r/[e-mail]/ # v2
Reviewed-by: Ilya Dryomov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

net/ceph/messenger_v1.c

···
 	return r;
 }
 
+/*
+ * @more: MSG_MORE or 0.
+ */
+static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
+			     int offset, size_t size, int more)
+{
+	struct msghdr msg = {
+		.msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL | more,
+	};
+	struct bio_vec bvec;
+	int ret;
+
+	/*
+	 * MSG_SPLICE_PAGES cannot properly handle pages with page_count == 0,
+	 * we need to fall back to sendmsg if that's the case.
+	 *
+	 * Same goes for slab pages: skb_can_coalesce() allows
+	 * coalescing neighboring slab objects into a single frag which
+	 * triggers one of hardened usercopy checks.
+	 */
+	if (sendpage_ok(page))
+		msg.msg_flags |= MSG_SPLICE_PAGES;
+
+	bvec_set_page(&bvec, page, size, offset);
+	iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bvec, 1, size);
+
+	ret = sock_sendmsg(sock, &msg);
+	if (ret == -EAGAIN)
+		ret = 0;
+
+	return ret;
+}
+
 static void con_out_kvec_reset(struct ceph_connection *con)
 {
 	BUG_ON(con->v1.out_skip);
···
 	 */
 	crc = do_datacrc ? le32_to_cpu(msg->footer.data_crc) : 0;
 	while (cursor->total_resid) {
-		struct bio_vec bvec;
-		struct msghdr msghdr = {
-			.msg_flags = MSG_SPLICE_PAGES,
-		};
 		struct page *page;
 		size_t page_offset;
 		size_t length;
···
 		}
 
 		page = ceph_msg_data_next(cursor, &page_offset, &length);
-		if (length != cursor->total_resid)
-			msghdr.msg_flags |= MSG_MORE;
-
-		bvec_set_page(&bvec, page, length, page_offset);
-		iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, length);
-
-		ret = sock_sendmsg(con->sock, &msghdr);
+		ret = ceph_tcp_sendpage(con->sock, page, page_offset, length,
+					MSG_MORE);
 		if (ret <= 0) {
 			if (do_datacrc)
 				msg->footer.data_crc = cpu_to_le32(crc);
···
  */
 static int write_partial_skip(struct ceph_connection *con)
 {
-	struct bio_vec bvec;
-	struct msghdr msghdr = {
-		.msg_flags = MSG_SPLICE_PAGES | MSG_MORE,
-	};
 	int ret;
 
 	dout("%s %p %d left\n", __func__, con, con->v1.out_skip);
 	while (con->v1.out_skip > 0) {
 		size_t size = min(con->v1.out_skip, (int)PAGE_SIZE);
 
-		if (size == con->v1.out_skip)
-			msghdr.msg_flags &= ~MSG_MORE;
-		bvec_set_page(&bvec, ZERO_PAGE(0), size, 0);
-		iov_iter_bvec(&msghdr.msg_iter, ITER_SOURCE, &bvec, 1, size);
-
-		ret = sock_sendmsg(con->sock, &msghdr);
+		ret = ceph_tcp_sendpage(con->sock, ceph_zero_page, 0, size,
+					MSG_MORE);
 		if (ret <= 0)
 			goto out;
 		con->v1.out_skip -= ret;

net/ceph/messenger_v2.c

···
 	return ret;
 }
 
+static int do_sendmsg(struct socket *sock, struct iov_iter *it)
+{
+	struct msghdr msg = { .msg_flags = CEPH_MSG_FLAGS };
+	int ret;
+
+	msg.msg_iter = *it;
+	while (iov_iter_count(it)) {
+		ret = sock_sendmsg(sock, &msg);
+		if (ret <= 0) {
+			if (ret == -EAGAIN)
+				ret = 0;
+			return ret;
+		}
+
+		iov_iter_advance(it, ret);
+	}
+
+	WARN_ON(msg_data_left(&msg));
+	return 1;
+}
+
+static int do_try_sendpage(struct socket *sock, struct iov_iter *it)
+{
+	struct msghdr msg = { .msg_flags = CEPH_MSG_FLAGS };
+	struct bio_vec bv;
+	int ret;
+
+	if (WARN_ON(!iov_iter_is_bvec(it)))
+		return -EINVAL;
+
+	while (iov_iter_count(it)) {
+		/* iov_iter_iovec() for ITER_BVEC */
+		bvec_set_page(&bv, it->bvec->bv_page,
+			      min(iov_iter_count(it),
+				  it->bvec->bv_len - it->iov_offset),
+			      it->bvec->bv_offset + it->iov_offset);
+
+		/*
+		 * MSG_SPLICE_PAGES cannot properly handle pages with
+		 * page_count == 0, we need to fall back to sendmsg if
+		 * that's the case.
+		 *
+		 * Same goes for slab pages: skb_can_coalesce() allows
+		 * coalescing neighboring slab objects into a single frag
+		 * which triggers one of hardened usercopy checks.
+		 */
+		if (sendpage_ok(bv.bv_page))
+			msg.msg_flags |= MSG_SPLICE_PAGES;
+		else
+			msg.msg_flags &= ~MSG_SPLICE_PAGES;
+
+		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE, &bv, 1, bv.bv_len);
+		ret = sock_sendmsg(sock, &msg);
+		if (ret <= 0) {
+			if (ret == -EAGAIN)
+				ret = 0;
+			return ret;
+		}
+
+		iov_iter_advance(it, ret);
+	}
+
+	return 1;
+}
+
 /*
  * Write as much as possible.  The socket is expected to be corked,
  * so we don't bother with MSG_MORE here.
  *
  * Return:
- *  >0 - done, nothing (else) to write
+ *   1 - done, nothing (else) to write
  *   0 - socket is full, need to wait
  *  <0 - error
  */
 static int ceph_tcp_send(struct ceph_connection *con)
 {
-	struct msghdr msg = {
-		.msg_iter	= con->v2.out_iter,
-		.msg_flags	= CEPH_MSG_FLAGS,
-	};
 	int ret;
-
-	if (WARN_ON(!iov_iter_is_bvec(&con->v2.out_iter)))
-		return -EINVAL;
-
-	if (con->v2.out_iter_sendpage)
-		msg.msg_flags |= MSG_SPLICE_PAGES;
 
 	dout("%s con %p have %zu try_sendpage %d\n", __func__, con,
 	     iov_iter_count(&con->v2.out_iter), con->v2.out_iter_sendpage);
-
-	ret = sock_sendmsg(con->sock, &msg);
-	if (ret > 0)
-		iov_iter_advance(&con->v2.out_iter, ret);
-	else if (ret == -EAGAIN)
-		ret = 0;
-
+	if (con->v2.out_iter_sendpage)
+		ret = do_try_sendpage(con->sock, &con->v2.out_iter);
+	else
+		ret = do_sendmsg(con->sock, &con->v2.out_iter);
 	dout("%s con %p ret %d left %zu\n", __func__, con, ret,
 	     iov_iter_count(&con->v2.out_iter));
 	return ret;