[PATCH 2/4] drbd: Fix variable dereference before check

The struct is 'req' is checked for NULL after resource was assigned from
a member from it.

Check 'req' for NULL before assigning resource.

Detected by Smatch:
drivers/block/drbd/drbd_req.c:1996 drbd_unplug() warn:
variable dereferenced before check 'req' (see line 1993)

Fixes: 71d075200b462 ("drbd: rework request processing for DRBD 9 multi-peer IO")
Signed-off-by: Ethan Tidmore <[email protected]>
---
 drivers/block/drbd/drbd_req.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index e88b5da15c1e..4cbd9ec15157 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -1990,12 +1990,14 @@ static void drbd_unplug(struct blk_plug_cb *cb, bool from_schedule)
 {
 	struct drbd_plug_cb *plug = container_of(cb, struct drbd_plug_cb, cb);
 	struct drbd_request *req = plug->most_recent_req;
-	struct drbd_resource *resource = req->device->resource;
+	struct drbd_resource *resource;
 
 	kfree(cb);
 	if (!req)
 		return;
 
+	resource = req->device->resource;
+
 	read_lock_irq(&resource->state_rwlock);
 	/* In case the sender did not process it yet, raise the flag to
 	 * have it followed with P_UNPLUG_REMOTE just after. */
-- 
2.53.0