From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 91FAC6B0005 for ; Mon, 5 Mar 2018 19:47:43 -0500 (EST) Received: by mail-pf0-f197.google.com with SMTP id h193so10585858pfe.14 for ; Mon, 05 Mar 2018 16:47:43 -0800 (PST) Received: from mga09.intel.com (mga09.intel.com. [134.134.136.24]) by mx.google.com with ESMTPS id y7si8079481pgy.161.2018.03.05.16.47.41 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Mar 2018 16:47:42 -0800 (PST) From: "Huang\, Ying" Subject: Re: [PATCH -V2 -mm] mm: Fix races between swapoff and flush dcache References: <20180305083634.15174-1-ying.huang@intel.com> Date: Tue, 06 Mar 2018 08:47:37 +0800 In-Reply-To: <20180305083634.15174-1-ying.huang@intel.com> (Ying Huang's message of "Mon, 5 Mar 2018 16:36:34 +0800") Message-ID: <871sgy2fo6.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Minchan Kim , Michal Hocko , Johannes Weiner , Mel Gorman , Dave Hansen , Chen Liqin , Russell King , Yoshinori Sato , "James E.J. Bottomley" , Guan Xuetao , "David S. Miller" , Chris Zankel , Vineet Gupta , Ley Foon Tan , Ralf Baechle , Andi Kleen "Huang, Ying" writes: > From: Huang Ying > > 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] -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org