drbd: fix potential deadlock during "restart" of conflicting writes

w_restart_write(), run from worker context, calls __drbd_make_request()
and further drbd_al_begin_io(, delegate=true), which then
potentially deadlocks.  The previous patch moved a BUG_ON to expose
such call paths, which would now be triggered.

Also, if we call __drbd_make_request() from resource worker context,
like w_restart_write() did, and that should block for whatever reason
(!drbd_state_is_stable(), resource suspended, ...),
we potentially deadlock the whole resource, as the worker
is needed for state changes and other things.

Create a dedicated retry workqueue for this instead.

Also make sure that inc_ap_bio()/dec_ap_bio() are properly paired,
even if do_retry() needs to retry itself,
in case __drbd_make_request() returns != 0.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

1 files changed, 3 insertions, 29 deletions

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 8a7f61ba74a8..b159ad15abe5 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -1748,30 +1748,6 @@ static int receive_RSDataReply(struct drbd_tconn *tconn, struct packet_info *pi)
 	return err;
 }
 
-static int w_restart_write(struct drbd_work *w, int cancel)
-{
-	struct drbd_request *req = container_of(w, struct drbd_request, w);
-	struct drbd_conf *mdev = w->mdev;
-	struct bio *bio;
-	unsigned long start_time;
-	unsigned long flags;
-
-	spin_lock_irqsave(&mdev->tconn->req_lock, flags);
-	if (!expect(req->rq_state & RQ_POSTPONED)) {
-		spin_unlock_irqrestore(&mdev->tconn->req_lock, flags);
-		return -EIO;
-	}
-	bio = req->master_bio;
-	start_time = req->start_time;
-	/* Postponed requests will not have their master_bio completed!  */
-	__req_mod(req, DISCARD_WRITE, NULL);
-	spin_unlock_irqrestore(&mdev->tconn->req_lock, flags);
-
-	while (__drbd_make_request(mdev, bio, start_time))
-		/* retry */ ;
-	return 0;
-}
-
 static void restart_conflicting_writes(struct drbd_conf *mdev,
 				       sector_t sector, int size)
 {
@@ -1785,11 +1761,9 @@ static void restart_conflicting_writes(struct drbd_conf *mdev,
 		if (req->rq_state & RQ_LOCAL_PENDING ||
 		    !(req->rq_state & RQ_POSTPONED))
 			continue;
-		if (expect(list_empty(&req->w.list))) {
-			req->w.mdev = mdev;
-			req->w.cb = w_restart_write;
-			drbd_queue_work(&mdev->tconn->data.work, &req->w);
-		}
+		/* as it is RQ_POSTPONED, this will cause it to
+		 * be queued on the retry workqueue. */
+		__req_mod(req, DISCARD_WRITE, NULL);
 	}
 }