lightnvm: pblk: prevent premature sync point resets

Unless we protect flush pointer updates with a lock, we risk
resetting new flush points before we've synced all sectors
up to that point.

This patch protects new flush points with the same spin lock
that is being held when advancing the sync pointer and
resetting completed flush points.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk-rb.c

@@ -367,17 +367,17 @@ static int pblk_rb_flush_point_set(struct pblk_rb *rb, struct bio *bio,
 	flush_point = (pos == 0) ? (rb->nr_entries - 1) : (pos - 1);
 	entry = &rb->entries[flush_point];
 
+	pblk_rb_sync_init(rb, NULL);
+
 	/* Protect flush points */
 	smp_store_release(&rb->flush_point, flush_point);
 
-	if (!bio)
-		return 0;
+	if (bio)
+		bio_list_add(&entry->w_ctx.bios, bio);
 
-	spin_lock_irq(&rb->s_lock);
-	bio_list_add(&entry->w_ctx.bios, bio);
-	spin_unlock_irq(&rb->s_lock);
+	pblk_rb_sync_end(rb, NULL);
 
-	return 1;
+	return bio ? 1 : 0;
 }
 
 static int __pblk_rb_may_write(struct pblk_rb *rb, unsigned int nr_entries,