lightnvm: pblk: fix race condition on metadata I/O

In pblk, when a new line is allocated, metadata for the previously
written line is scheduled. This is done through a fixed memory region
that is shared through time and contexts across different lines and
therefore protected by a lock. Unfortunately, this lock is not properly
covering all the metadata used for sharing this memory regions,
resulting in a race condition.

This patch fixes this race condition by protecting this metadata
properly.

Fixes: dd2a434 ("lightnvm: pblk: sched. metadata on write thread")
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk-write.c

@@ -417,12 +417,11 @@ int pblk_submit_meta_io(struct pblk *pblk, struct pblk_line *meta_line)
 			rqd->ppa_list[i] = addr_to_gen_ppa(pblk, paddr, id);
 	}
 
+	spin_lock(&l_mg->close_lock);
 	emeta->mem += rq_len;
-	if (emeta->mem >= lm->emeta_len[0]) {
-		spin_lock(&l_mg->close_lock);
+	if (emeta->mem >= lm->emeta_len[0])
 		list_del(&meta_line->list);
-		spin_unlock(&l_mg->close_lock);
-	}
+	spin_unlock(&l_mg->close_lock);
 
 	pblk_down_page(pblk, rqd->ppa_list, rqd->nr_ppas);
 
@@ -491,14 +490,15 @@ static struct pblk_line *pblk_should_submit_meta_io(struct pblk *pblk,
 	struct pblk_line *meta_line;
 
 	spin_lock(&l_mg->close_lock);
-retry:
 	if (list_empty(&l_mg->emeta_list)) {
 		spin_unlock(&l_mg->close_lock);
 		return NULL;
 	}
 	meta_line = list_first_entry(&l_mg->emeta_list, struct pblk_line, list);
-	if (meta_line->emeta->mem >= lm->emeta_len[0])
-		goto retry;
+	if (meta_line->emeta->mem >= lm->emeta_len[0]) {
+		spin_unlock(&l_mg->close_lock);
+		return NULL;
+	}
 	spin_unlock(&l_mg->close_lock);
 
 	if (!pblk_valid_meta_ppa(pblk, meta_line, data_rqd))