From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 998D582963 for ; Thu, 21 Jul 2016 06:29:15 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id b65so10165540wmg.0 for ; Thu, 21 Jul 2016 03:29:15 -0700 (PDT) Received: from mail-wm0-f67.google.com (mail-wm0-f67.google.com. [74.125.82.67]) by mx.google.com with ESMTPS id y135si2627818wmc.71.2016.07.21.03.29.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 21 Jul 2016 03:29:13 -0700 (PDT) Received: by mail-wm0-f67.google.com with SMTP id q128so2020695wma.1 for ; Thu, 21 Jul 2016 03:29:13 -0700 (PDT) Date: Thu, 21 Jul 2016 12:29:11 +0200 From: Michal Hocko Subject: Re: + mm-hugetlb-fix-race-when-migrate-pages.patch added to -mm tree Message-ID: <20160721102911.GF26379@dhcp22.suse.cz> References: <578eb28b.YbRUDGz5RloTVlrE%akpm@linux-foundation.org> <20160721074340.GA26398@dhcp22.suse.cz> <20160721081355.GB25398@hori1.linux.bs1.fc.nec.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160721081355.GB25398@hori1.linux.bs1.fc.nec.co.jp> Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: "akpm@linux-foundation.org" , "zhongjiang@huawei.com" , "qiuxishi@huawei.com" , "vbabka@suse.cz" , "mm-commits@vger.kernel.org" , Mike Kravetz , Mel Gorman , "linux-mm@kvack.org" On Thu 21-07-16 08:13:55, Naoya Horiguchi wrote: > On Thu, Jul 21, 2016 at 09:43:40AM +0200, Michal Hocko wrote: > > We have further discussed the patch and I believe it is not correct. See [1]. > > I am proposing the following alternative. > > > > [1] http://lkml.kernel.org/r/20160720132431.GM11249@dhcp22.suse.cz > > --- > > From b1e9b3214f1859fdf7d134cdcb56f5871933539c Mon Sep 17 00:00:00 2001 > > From: Michal Hocko > > Date: Thu, 21 Jul 2016 09:28:13 +0200 > > Subject: [PATCH] mm, hugetlb: fix huge_pte_alloc BUG_ON > > > > Zhong Jiang has reported a BUG_ON from huge_pte_alloc hitting when he > > runs his database load with memory online and offline running in > > parallel. The reason is that huge_pmd_share might detect a shared pmd > > which is currently migrated and so it has migration pte which is > > !pte_huge. > > > > There doesn't seem to be any easy way to prevent from the race and in > > fact seeing the migration swap entry is not harmful. Both callers of > > huge_pte_alloc are prepared to handle them. copy_hugetlb_page_range > > will copy the swap entry and make it COW if needed. hugetlb_fault will > > back off and so the page fault is retries if the page is still under > > migration and waits for its completion in hugetlb_fault. > > > > That means that the BUG_ON is wrong and we should update it. Let's > > simply check that all present ptes are pte_huge instead. > > > > Reported-by: zhongjiang > > Signed-off-by: Michal Hocko > > In the early days of hugetlb, we had an assumption that !pte_none is > equivalent to pmd_present() because there was no valid non-present entry > on huge_pte. Situation has changed by hugepage migration and/or hwpoison, > so we have to care about the separation of these two, and make sure that > pte_present is true before checking pte_huge. > > So I think this change is right. Thank you Zhong, Michal. > > Acked-by: Naoya Horiguchi Thank you for double checking Naoya! IIUC Fixes: 290408d4a250 ("hugetlb: hugepage migration core") should help. Maybe we should even tag that for stable? -- Michal Hocko SUSE Labs -- 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