pktdvd: stop using bdi congestion framework.

The bdi congestion framework isn't widely used and should be
deprecated.

pktdvd makes use of it to track congestion, but this can be done
entirely internally to pktdvd, so it doesn't need to use the framework.

So introduce a "congested" flag.  When waiting for bio_queue_size to
drop, set this flag and a var_waitqueue() to wait for it.  When
bio_queue_size does drop and this flag is set, clear the flag and call
wake_up_var().

We don't use a wait_var_event macro for the waiting as we need to set
the flag and drop the spinlock before calling schedule() and while that
is possible with __wait_var_event(), result is not easy to read.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: NeilBrown <neilb@suse.de>
Link: https://lore.kernel.org/r/163910843527.9928.857338663717630212@noble.neil.brown.name
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/pktcdvd.c

@@ -1107,7 +1107,6 @@ static int pkt_handle_queue(struct pktcdvd_device *pd)
 	sector_t zone = 0; /* Suppress gcc warning */
 	struct pkt_rb_node *node, *first_node;
 	struct rb_node *n;
-	int wakeup;
 
 	atomic_set(&pd->scan_queue, 0);
 
@@ -1179,12 +1178,14 @@ try_next_bio:
 		spin_unlock(&pkt->lock);
 	}
 	/* check write congestion marks, and if bio_queue_size is
-	   below, wake up any waiters */
+	 * below, wake up any waiters
-	wakeup = (pd->write_congestion_on > 0
+	 */
-	 		&& pd->bio_queue_size <= pd->write_congestion_off);
+	if (pd->congested &&
+	    pd->bio_queue_size <= pd->write_congestion_off) {
+		pd->congested = false;
+		wake_up_var(&pd->congested);
+	}
 	spin_unlock(&pd->lock);
-	if (wakeup)
-		clear_bdi_congested(pd->disk->bdi, BLK_RW_ASYNC);
 
 	pkt->sleep_time = max(PACKET_WAIT_TIME, 1);
 	pkt_set_state(pkt, PACKET_WAITING_STATE);
@@ -2364,12 +2365,20 @@ static void pkt_make_request_write(struct request_queue *q, struct bio *bio)
 	spin_lock(&pd->lock);
 	if (pd->write_congestion_on > 0
 	    && pd->bio_queue_size >= pd->write_congestion_on) {
-		set_bdi_congested(bio->bi_bdev->bd_disk->bdi, BLK_RW_ASYNC);
+		struct wait_bit_queue_entry wqe;
-		do {
+
+		init_wait_var_entry(&wqe, &pd->congested, 0);
+		for (;;) {
+			prepare_to_wait_event(__var_waitqueue(&pd->congested),
+					      &wqe.wq_entry,
+					      TASK_UNINTERRUPTIBLE);
+			if (pd->bio_queue_size <= pd->write_congestion_off)
+				break;
+			pd->congested = true;
 			spin_unlock(&pd->lock);
-			congestion_wait(BLK_RW_ASYNC, HZ);
+			schedule();
 			spin_lock(&pd->lock);
-		} while(pd->bio_queue_size > pd->write_congestion_off);
+		}
 	}
 	spin_unlock(&pd->lock);
 

include/linux/pktcdvd.h

@@ -183,6 +183,8 @@ struct pktcdvd_device
 	spinlock_t		lock;		/* Serialize access to bio_queue */
 	struct rb_root		bio_queue;	/* Work queue of bios we need to handle */
 	int			bio_queue_size;	/* Number of nodes in bio_queue */
+	bool			congested;	/* Someone is waiting for bio_queue_size
+						 * to drop. */
 	sector_t		current_sector;	/* Keep track of where the elevator is */
 	atomic_t		scan_queue;	/* Set to non-zero when pkt_handle_queue */
 						/* needs to be run. */