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authorColy Li <colyli@suse.de>2019-06-28 19:59:56 +0800
committerJens Axboe <axboe@kernel.dk>2019-06-28 07:39:17 -0600
commit41508bb7d46b74dba631017e5a702a86caf1db8c (patch)
tree72a7cc87407d048751e2ab6e676a3969f3b6caa4 /drivers/md/bcache
parente5ec5f4765ada9c75fb3eee93a6e72f0e50599d5 (diff)
downloadlinux-41508bb7d46b74dba631017e5a702a86caf1db8c.tar.bz2
bcache: add comments for mutex_lock(&b->write_lock)
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>
Diffstat (limited to 'drivers/md/bcache')
-rw-r--r--drivers/md/bcache/btree.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 88e5aa3fbb07..846306c3a887 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -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);