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authorGlauber Costa <glommer@gmail.com>2013-08-28 04:18:03 +0400
committerAl Viro <viro@zeniv.linux.org.uk>2013-09-11 02:56:31 +0400
commit4e717f5c1083995c334ced639cc77a75e9972567 (patch)
treef236061b46b4401913652b167798210132d611ad /fs/drop_caches.c
parent6a4f496fd2fc74fa036732ae52c184952d6e3e37 (diff)
downloadlinux-4e717f5c1083995c334ced639cc77a75e9972567.tar.xz
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 <glommer@openvz.org> Cc: Michal Hocko <mhocko@suse.cz> Acked-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/drop_caches.c')
0 files changed, 0 insertions, 0 deletions