From 4e717f5c1083995c334ced639cc77a75e9972567 Mon Sep 17 00:00:00 2001 From: Glauber Costa Date: Wed, 28 Aug 2013 10:18:03 +1000 Subject: list_lru: remove special case function list_lru_dispose_all. The list_lru implementation has one function, list_lru_dispose_all, with only one user (the dentry code). At first, such function appears to make sense because we are really not interested in the result of isolating each dentry separately - all of them are going away anyway. However, it's implementation is buggy in the following way: When we call list_lru_dispose_all in fs/dcache.c, we scan all dentries marking them with DCACHE_SHRINK_LIST. However, this is done without the nlru->lock taken. The imediate result of that is that someone else may add or remove the dentry from the LRU at the same time. When list_lru_del happens in that scenario we will see an element that is not yet marked with DCACHE_SHRINK_LIST (even though it will be in the future) and obviously remove it from an lru where the element no longer is. Since list_lru_dispose_all will in effect count down nlru's nr_items and list_lru_del will do the same, this will lead to an imbalance. The solution for this would not be so simple: we can obviously just keep the lru_lock taken, but then we have no guarantees that we will be able to acquire the dentry lock (dentry->d_lock). To properly solve this, we need a communication mechanism between the lru and dentry code, so they can coordinate this with each other. Such mechanism already exists in the form of the list_lru_walk_cb callback. So it is possible to construct a dcache-side prune function that does the right thing only by calling list_lru_walk in a loop until no more dentries are available. With only one user, plus the fact that a sane solution for the problem would involve boucing between dcache and list_lru anyway, I see little justification to keep the special case list_lru_dispose_all in tree. Signed-off-by: Glauber Costa Cc: Michal Hocko Acked-by: Dave Chinner Signed-off-by: Andrew Morton Signed-off-by: Al Viro --- include/linux/list_lru.h | 17 ----------------- 1 file changed, 17 deletions(-) (limited to 'include/linux/list_lru.h') diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h index 2fe13e1a809a..4d02ad3badab 100644 --- a/include/linux/list_lru.h +++ b/include/linux/list_lru.h @@ -137,21 +137,4 @@ list_lru_walk(struct list_lru *lru, list_lru_walk_cb isolate, } return isolated; } - -typedef void (*list_lru_dispose_cb)(struct list_head *dispose_list); -/** - * list_lru_dispose_all: forceably flush all elements in an @lru - * @lru: the lru pointer - * @dispose: callback function to be called for each lru list. - * - * This function will forceably isolate all elements into the dispose list, and - * call the @dispose callback to flush the list. Please note that the callback - * should expect items in any state, clean or dirty, and be able to flush all of - * them. - * - * Return value: how many objects were freed. It should be equal to all objects - * in the list_lru. - */ -unsigned long -list_lru_dispose_all(struct list_lru *lru, list_lru_dispose_cb dispose); #endif /* _LRU_LIST_H */ -- cgit v1.2.1