bcache: add comments for mutex_lock(&b->write_lock) (41508bb7) · Commits · 戴 / test

When accessing or modifying BTREE_NODE_dirty bit, it is not always necessary to acquire b->write_lock. In bch_btree_cache_free() and mca_reap() acquiring b->write_lock is necessary, and this patch adds comments to explain why mutex_lock(&b->write_lock) is necessary for checking or clearing BTREE_NODE_dirty bit there. Signed-off-by:

Coly Li <colyli@suse.de> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

drivers/md/bcache/btree.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -659,6 +659,11 @@ static int mca_reap(struct btree *b, unsigned int min_order, bool flush)
		up(&b->io_mutex);
		}

		/*
		* BTREE_NODE_dirty might be cleared in btree_flush_btree() by
		* __bch_btree_node_write(). To avoid an extra flush, acquire
		* b->write_lock before checking BTREE_NODE_dirty bit.
		*/
		mutex_lock(&b->write_lock);
		if (btree_node_dirty(b))
		__bch_btree_node_write(b, &cl);
		@@ -782,6 +787,11 @@ void bch_btree_cache_free(struct cache_set *c)
		while (!list_empty(&c->btree_cache)) {
		b = list_first_entry(&c->btree_cache, struct btree, list);

		/*
		* This function is called by cache_set_free(), no I/O
		* request on cache now, it is unnecessary to acquire
		* b->write_lock before clearing BTREE_NODE_dirty anymore.
		*/
		if (btree_node_dirty(b)) {
		btree_complete_write(b, btree_current_write(b));
		clear_bit(BTREE_NODE_dirty, &b->flags);

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