4.4-stable review patch. If anyone has any objections, please let me know.
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From: Huang Ying ying.huang@intel.com
[ Upstream commit e92bb4dd9673945179b1fc738c9817dd91bfb629 ]
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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/vmscan.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
--- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3841,7 +3841,13 @@ int zone_reclaim(struct zone *zone, gfp_ */ 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