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 --- arch/parisc/kernel/cache.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'arch/parisc') diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c index e3b45546d589..a99da95fc9fd 100644 --- a/arch/parisc/kernel/cache.c +++ b/arch/parisc/kernel/cache.c @@ -88,7 +88,8 @@ update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *ptep) return; page = pfn_to_page(pfn); - if (page_mapping(page) && test_bit(PG_dcache_dirty, &page->flags)) { + if (page_mapping_file(page) && + test_bit(PG_dcache_dirty, &page->flags)) { flush_kernel_dcache_page_addr(pfn_va(pfn)); clear_bit(PG_dcache_dirty, &page->flags); } else if (parisc_requires_coherency()) @@ -304,7 +305,7 @@ __flush_cache_page(struct vm_area_struct *vma, unsigned long vmaddr, void flush_dcache_page(struct page *page) { - struct address_space *mapping = page_mapping(page); + struct address_space *mapping = page_mapping_file(page); struct vm_area_struct *mpnt; unsigned long offset; unsigned long addr, old_addr = 0; -- cgit v1.2.1