[PATCH v5 2/3] nvme-tcp: check page by sendpage_ok() before calling kernel_sendpage()

[Coly Li]

Currently nvme_tcp_try_send_data() doesn't use kernel_sendpage() to
send slab pages. But for pages allocated by __get_free_pages() without
__GFP_COMP, which also have refcount as 0, they are still sent by
kernel_sendpage() to remote end, this is problematic.

The new introduced helper sendpage_ok() checks both PageSlab tag and
page_count counter, and returns true if the checking page is OK to be
sent by kernel_sendpage().

This patch fixes the page checking issue of nvme_tcp_try_send_data()
with sendpage_ok(). If sendpage_ok() returns true, send this page by
kernel_sendpage(), otherwise use sock_no_sendpage to handle this page.

Signed-off-by: Coly Li <colyli@xxxxxxx>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Mikhail Skorzhinskii <mskorzhinskiy@xxxxxxxxxxxxxx>
Cc: Philipp Reisner <philipp.reisner@xxxxxxxxxx>
Cc: Sagi Grimberg <sagi@xxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
Changelog:
v4, change sendpage_ok() as an inline helper, and post it as
    separate patch.
v3, introduce a more common sendpage_ok()
v2, fix typo in patch subject
v1, the initial version.
 drivers/nvme/host/tcp.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 62fbaecdc960..902fe742762b 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -912,12 +912,11 @@ static int nvme_tcp_try_send_data(struct nvme_tcp_request *req)
 		else
 			flags |= MSG_MORE | MSG_SENDPAGE_NOTLAST;
 
-		/* can't zcopy slab pages */
-		if (unlikely(PageSlab(page))) {
-			ret = sock_no_sendpage(queue->sock, page, offset, len,
+		if (sendpage_ok(page)) {
+			ret = kernel_sendpage(queue->sock, page, offset, len,
 					flags);
 		} else {
-			ret = kernel_sendpage(queue->sock, page, offset, len,
+			ret = sock_no_sendpage(queue->sock, page, offset, len,
 					flags);
 		}
 		if (ret <= 0)
-- 
2.26.2