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authorHuang Ying <ying.huang@intel.com>2018-04-05 16:23:20 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2018-04-05 21:36:25 -0700
commite92bb4dd9673945179b1fc738c9817dd91bfb629 (patch)
tree618a868ab40bcd5e2f5c2830341b47f6cffa6afe /mm/vmscan.c
parent5ad3509364a86461188184e2ae7ca517dca6f389 (diff)
downloadlinux-e92bb4dd9673945179b1fc738c9817dd91bfb629.tar.bz2
mm: fix races between address_space dereference and free in page_evicatable
When page_mapping() is called and the mapping is dereferenced in page_evicatable() through shrink_active_list(), it is possible for the inode to be truncated and the embedded address space to be freed at the same time. This may lead to the following race. CPU1 CPU2 truncate(inode) shrink_active_list() ... page_evictable(page) truncate_inode_page(mapping, page); delete_from_page_cache(page) spin_lock_irqsave(&mapping->tree_lock, flags); __delete_from_page_cache(page, NULL) page_cache_tree_delete(..) ... mapping = page_mapping(page); page->mapping = NULL; ... spin_unlock_irqrestore(&mapping->tree_lock, flags); page_cache_free_page(mapping, page) put_page(page) if (put_page_testzero(page)) -> false - inode now has no pages and can be freed including embedded address_space mapping_unevictable(mapping) test_bit(AS_UNEVICTABLE, &mapping->flags); - we've dereferenced mapping which is potentially already free. Similar race exists between swap cache freeing and page_evicatable() too. The address_space in inode and swap cache will be freed after a RCU grace period. So the races are fixed via enclosing the page_mapping() and address_space usage in rcu_read_lock/unlock(). Some comments are added in code to make it clear what is protected by the RCU read lock. Link: http://lkml.kernel.org/r/20180212081227.1940-1-ying.huang@intel.com Signed-off-by: "Huang, Ying" <ying.huang@intel.com> Reviewed-by: Jan Kara <jack@suse.cz> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Minchan Kim <minchan@kernel.org> Cc: "Huang, Ying" <ying.huang@intel.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/vmscan.c')
-rw-r--r--mm/vmscan.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index cd5dc3faaa57..ca566640c448 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3877,7 +3877,13 @@ int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
*/
int page_evictable(struct page *page)
{
- return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
+ int ret;
+
+ /* Prevent address_space of inode and swap cache from being freed */
+ rcu_read_lock();
+ ret = !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
+ rcu_read_unlock();
+ return ret;
}
#ifdef CONFIG_SHMEM