From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 999CBC6778F for ; Wed, 25 Jul 2018 10:32:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4F3CA2088E for ; Wed, 25 Jul 2018 10:32:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F3CA2088E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728775AbeGYLnL (ORCPT ); Wed, 25 Jul 2018 07:43:11 -0400 Received: from mx2.suse.de ([195.135.220.15]:40044 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728651AbeGYLnL (ORCPT ); Wed, 25 Jul 2018 07:43:11 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 4948FAEB6; Wed, 25 Jul 2018 10:32:06 +0000 (UTC) Date: Wed, 25 Jul 2018 12:32:04 +0200 From: Michal Hocko To: "zhaowuyun@wingtech.com" Cc: mgorman , akpm , minchan , vinmenon , hannes , "hillf.zj" , linux-mm , linux-kernel , Hugh Dickins Subject: Re: Re: [PATCH] [PATCH] mm: disable preemption before swapcache_free Message-ID: <20180725103204.GY28386@dhcp22.suse.cz> References: <2018072514375722198958@wingtech.com> <20180725074009.GU28386@dhcp22.suse.cz> <2018072515575576668668@wingtech.com> <20180725082100.GV28386@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180725082100.GV28386@dhcp22.suse.cz> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 25-07-18 10:21:00, Michal Hocko wrote: > [Please do not top post - thank you] > [CC Hugh - the original patch was http://lkml.kernel.org/r/2018072514375722198958@wingtech.com] now for real > On Wed 25-07-18 15:57:55, zhaowuyun@wingtech.com wrote: > > That is a BUG we found in mm/vmscan.c at KERNEL VERSION 4.9.82 > > The code is quite similar in the current tree as well. > > > Sumary is TASK A (normal priority) doing __remove_mapping page preempted by TASK B (RT priority) doing __read_swap_cache_async, > > the TASK A preempted before swapcache_free, left SWAP_HAS_CACHE flag in the swap cache, > > the TASK B which doing __read_swap_cache_async, will not success at swapcache_prepare(entry) because the swap cache was exist, then it will loop forever because it is a RT thread... > > the spin lock unlocked before swapcache_free, so disable preemption until swapcache_free executed ... > > OK, I see your point now. I have missed the lock is dropped before > swapcache_free. How can preemption disabling prevent this race to happen > while the code is preempted by an IRQ? -- Michal Hocko SUSE Labs