From cb9f753a3731f7fe16447bea45cb6f8e8bb432fb Mon Sep 17 00:00:00 2001 From: Huang Ying Date: Thu, 5 Apr 2018 16:24:39 -0700 Subject: mm: fix races between swapoff and flush dcache Thanks to commit 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB trunks"), after swapoff the address_space associated with the swap device will be freed. So page_mapping() users which may touch the address_space need some kind of mechanism to prevent the address_space from being freed during accessing. The dcache flushing functions (flush_dcache_page(), etc) in architecture specific code may access the address_space of swap device for anonymous pages in swap cache via page_mapping() function. But in some cases there are no mechanisms to prevent the swap device from being swapoff, for example, CPU1 CPU2 __get_user_pages() swapoff() flush_dcache_page() mapping = page_mapping() ... exit_swap_address_space() ... kvfree(spaces) mapping_mapped(mapping) The address space may be accessed after being freed. But from cachetlb.txt and Russell King, flush_dcache_page() only care about file cache pages, for anonymous pages, flush_anon_page() should be used. The implementation of flush_dcache_page() in all architectures follows this too. They will check whether page_mapping() is NULL and whether mapping_mapped() is true to determine whether to flush the dcache immediately. And they will use interval tree (mapping->i_mmap) to find all user space mappings. While mapping_mapped() and mapping->i_mmap isn't used by anonymous pages in swap cache at all. So, to fix the race between swapoff and flush dcache, __page_mapping() is add to return the address_space for file cache pages and NULL otherwise. All page_mapping() invoking in flush dcache functions are replaced with page_mapping_file(). [akpm@linux-foundation.org: simplify page_mapping_file(), per Mike] Link: http://lkml.kernel.org/r/20180305083634.15174-1-ying.huang@intel.com Signed-off-by: "Huang, Ying" Reviewed-by: Andrew Morton Cc: Minchan Kim Cc: Michal Hocko Cc: Johannes Weiner Cc: Mel Gorman Cc: Dave Hansen Cc: Chen Liqin Cc: Russell King Cc: Yoshinori Sato Cc: "James E.J. Bottomley" Cc: Guan Xuetao Cc: "David S. Miller" Cc: Chris Zankel Cc: Vineet Gupta Cc: Ley Foon Tan Cc: Ralf Baechle Cc: Andi Kleen Cc: Mike Rapoport Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/util.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'mm/util.c') diff --git a/mm/util.c b/mm/util.c index c1250501364f..029fc2f3b395 100644 --- a/mm/util.c +++ b/mm/util.c @@ -515,6 +515,16 @@ struct address_space *page_mapping(struct page *page) } EXPORT_SYMBOL(page_mapping); +/* + * For file cache pages, return the address_space, otherwise return NULL + */ +struct address_space *page_mapping_file(struct page *page) +{ + if (unlikely(PageSwapCache(page))) + return NULL; + return page_mapping(page); +} + /* Slow path of page_mapcount() for compound pages */ int __page_mapcount(struct page *page) { -- cgit v1.2.3