[PATCH] drbd: correctly submit flush bio on barrier

[Christoph Böhmwalder]

When we receive a flush command (or "barrier" in DRBD), we currently use
a REQ_OP_FLUSH with the REQ_PREFLUSH flag set.

The correct way to submit a flush bio is by using a REQ_OP_WRITE without
any data, and set the REQ_PREFLUSH flag.

Since commit b4a6bb3a67aa ("block: add a sanity check for non-write
flush/fua bios"), this triggers a warning in the block layer, but this
has been broken for quite some time before that.

So use the correct set of flags to actually make the flush happen.

Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: f9ff0da56437 ("drbd: allow parallel flushes for multi-volume resources")
Reported-by: Thomas Voegtle <tv@xxxxxxxx>
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@xxxxxxxxxx>
---
Previous, incorrect version of this patch:
https://lore.kernel.org/all/20230502092922.175857-1-christoph.boehmwalder@xxxxxxxxxx/

 drivers/block/drbd/drbd_receiver.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index e54404c632e7..34b112752ab1 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -1283,7 +1283,7 @@ static void one_flush_endio(struct bio *bio)
 static void submit_one_flush(struct drbd_device *device, struct issue_flush_context *ctx)
 {
 	struct bio *bio = bio_alloc(device->ldev->backing_bdev, 0,
-				    REQ_OP_FLUSH | REQ_PREFLUSH, GFP_NOIO);
+				    REQ_OP_WRITE | REQ_PREFLUSH, GFP_NOIO);
 	struct one_flush_context *octx = kmalloc(sizeof(*octx), GFP_NOIO);
 
 	if (!octx) {
-- 
2.39.2