"Huang, Ying" <[email protected]> writes: > From: Huang Ying <[email protected]> > > From commit 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB > trunks") on, 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().
Sorry, I just found I forgot replacing __page_mapping() to page_mapping_file() in the above paragraph. Could you help me to change it in place? Or I should resend the patch with the updated description? Best Regards, Huang, Ying [snip]
