bcachefs: Fix deadlock on -ENOSPC w.r.t. partial open buckets

Open buckets on the partial list should not count as allocated when
we're trying to allocate from the partial list.

Signed-off-by: Kent Overstreet <[email protected]>

Author: Kent Overstreet

fs/bcachefs/alloc_foreground.c

@@ -162,6 +162,10 @@ static void open_bucket_free_unused(struct bch_fs *c, struct open_bucket *ob)
 	       ARRAY_SIZE(c->open_buckets_partial));
 
 	spin_lock(&c->freelist_lock);
+	rcu_read_lock();
+	bch2_dev_rcu(c, ob->dev)->nr_partial_buckets++;
+	rcu_read_unlock();
+
 	ob->on_partial_list = true;
 	c->open_buckets_partial[c->open_buckets_partial_nr++] =
 		ob - c->open_buckets;
@@ -972,7 +976,7 @@ static int bucket_alloc_set_partial(struct bch_fs *c,
 			u64 avail;
 
 			bch2_dev_usage_read_fast(ca, &usage);
-			avail = dev_buckets_free(ca, usage, watermark);
+			avail = dev_buckets_free(ca, usage, watermark) + ca->nr_partial_buckets;
 			if (!avail)
 				continue;
 
@@ -981,6 +985,10 @@ static int bucket_alloc_set_partial(struct bch_fs *c,
 					  i);
 			ob->on_partial_list = false;
 
+			rcu_read_lock();
+			bch2_dev_rcu(c, ob->dev)->nr_partial_buckets--;
+			rcu_read_unlock();
+
 			ret = add_new_bucket(c, ptrs, devs_may_alloc,
 					     nr_replicas, nr_effective,
 					     have_cache, ob);
@@ -1191,7 +1199,13 @@ void bch2_open_buckets_stop(struct bch_fs *c, struct bch_dev *ca,
 			--c->open_buckets_partial_nr;
 			swap(c->open_buckets_partial[i],
 			     c->open_buckets_partial[c->open_buckets_partial_nr]);
+
 			ob->on_partial_list = false;
+
+			rcu_read_lock();
+			bch2_dev_rcu(c, ob->dev)->nr_partial_buckets--;
+			rcu_read_unlock();
+
 			spin_unlock(&c->freelist_lock);
 			bch2_open_bucket_put(c, ob);
 			spin_lock(&c->freelist_lock);

fs/bcachefs/bcachefs.h

@@ -555,6 +555,7 @@ struct bch_dev {
 	u64			alloc_cursor[3];
 
 	unsigned		nr_open_buckets;
+	unsigned		nr_partial_buckets;
 	unsigned		nr_btree_reserve;
 
 	size_t			inc_gen_needs_gc;