Commit 05335cff authored by Kent Overstreet's avatar Kent Overstreet
Browse files

bcache: Fix a race when freeing btree nodes 



This isn't a bulletproof fix; btree_node_free() -> bch_bucket_free() puts the
bucket on the unused freelist, where it can be reused right away without any
ordering requirements. It would be better to wait on at least a journal write to
go down before reusing the bucket. bch_btree_set_root() does this, and inserting
into non leaf nodes is completely synchronous so we should be ok, but future
patches are just going to get rid of the unused freelist - it was needed in the
past for various reasons but shouldn't be anymore.

Signed-off-by: default avatarKent Overstreet <kmo@daterainc.com>
parent 4fe6a816

drivers/md/bcache/btree.c

+20 −33
Original line number Diff line number Diff line
@@ -1006,8 +1006,6 @@ static void btree_node_prefetch(struct cache_set *c, struct bkey *k, int level) 


static void btree_node_free(struct btree *b)

{

	unsigned i;



	trace_bcache_btree_node_free(b);



	BUG_ON(b == b->c->root);
@@ -1019,14 +1017,6 @@ static void btree_node_free(struct btree *b) 
	cancel_delayed_work(&b->work);



	mutex_lock(&b->c->bucket_lock);



	for (i = 0; i < KEY_PTRS(&b->key); i++) {

		BUG_ON(atomic_read(&PTR_BUCKET(b->c, &b->key, i)->pin));



		bch_inc_gen(PTR_CACHE(b->c, &b->key, i),

			    PTR_BUCKET(b->c, &b->key, i));

	}



	bch_bucket_free(b->c, &b->key);

	mca_bucket_free(b);

	mutex_unlock(&b->c->bucket_lock);
@@ -1086,16 +1076,19 @@ static void make_btree_freeing_key(struct btree *b, struct bkey *k) 
{

	unsigned i;



	mutex_lock(&b->c->bucket_lock);



	atomic_inc(&b->c->prio_blocked);



	bkey_copy(k, &b->key);

	bkey_copy_key(k, &ZERO_KEY);



	for (i = 0; i < KEY_PTRS(k); i++) {

		uint8_t g = PTR_BUCKET(b->c, k, i)->gen + 1;



		SET_PTR_GEN(k, i, g);

	}

	for (i = 0; i < KEY_PTRS(k); i++)

		SET_PTR_GEN(k, i,

			    bch_inc_gen(PTR_CACHE(b->c, &b->key, i),

					PTR_BUCKET(b->c, &b->key, i)));



	atomic_inc(&b->c->prio_blocked);

	mutex_unlock(&b->c->bucket_lock);

}



static int btree_check_reserve(struct btree *b, struct btree_op *op)
@@ -1342,6 +1335,13 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op, 
		bch_keylist_add(keylist, &new_nodes[i]->key);

	}



	closure_sync(&cl);



	/* We emptied out this node */

	BUG_ON(btree_bset_first(new_nodes[0])->keys);

	btree_node_free(new_nodes[0]);

	rw_unlock(true, new_nodes[0]);



	for (i = 0; i < nodes; i++) {

		if (__bch_keylist_realloc(keylist, bkey_u64s(&r[i].b->key)))

			goto out_nocoalesce;
@@ -1350,12 +1350,8 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op, 
		bch_keylist_push(keylist);

	}



	/* We emptied out this node */

	BUG_ON(btree_bset_first(new_nodes[0])->keys);

	btree_node_free(new_nodes[0]);

	rw_unlock(true, new_nodes[0]);



	closure_sync(&cl);

	bch_btree_insert_node(b, op, keylist, NULL, NULL);

	BUG_ON(!bch_keylist_empty(keylist));



	for (i = 0; i < nodes; i++) {

		btree_node_free(r[i].b);
@@ -1364,9 +1360,6 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op, 
		r[i].b = new_nodes[i];

	}



	bch_btree_insert_node(b, op, keylist, NULL, NULL);

	BUG_ON(!bch_keylist_empty(keylist));



	memmove(r, r + 1, sizeof(r[0]) * (nodes - 1));

	r[nodes - 1].b = ERR_PTR(-EINTR);
@@ -1456,12 +1449,11 @@ static int btree_gc_recurse(struct btree *b, struct btree_op *op, 
							       keys.top);

					bch_keylist_push(&keys);



					btree_node_free(last->b);



					bch_btree_insert_node(b, op, &keys,

							      NULL, NULL);

					BUG_ON(!bch_keylist_empty(&keys));



					btree_node_free(last->b);

					rw_unlock(true, last->b);

					last->b = n;
@@ -1924,26 +1916,21 @@ static int btree_split(struct btree *b, struct btree_op *op, 
		closure_sync(&cl);

		bch_btree_set_root(n3);

		rw_unlock(true, n3);



		btree_node_free(b);

	} else if (!b->parent) {

		/* Root filled up but didn't need to be split */

		closure_sync(&cl);

		bch_btree_set_root(n1);



		btree_node_free(b);

	} else {

		/* Split a non root node */

		closure_sync(&cl);

		make_btree_freeing_key(b, parent_keys.top);

		bch_keylist_push(&parent_keys);



		btree_node_free(b);



		bch_btree_insert_node(b->parent, op, &parent_keys, NULL, NULL);

		BUG_ON(!bch_keylist_empty(&parent_keys));

	}



	btree_node_free(b);

	rw_unlock(true, n1);



	bch_time_stats_update(&b->c->btree_split_time, start_time);

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