From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752301AbdESQ7V (ORCPT ); Fri, 19 May 2017 12:59:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43450 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750831AbdESQ7T (ORCPT ); Fri, 19 May 2017 12:59:19 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com DD7E2C0467C5 Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jglisse@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com DD7E2C0467C5 From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= To: , linux-mm@kvack.org Cc: =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , "Kirill A. Shutemov" , Andrew Morton , Ingo Molnar , Michal Hocko , Mel Gorman Subject: [PATCH] x86/mm: pgds getting out of sync after memory hot remove Date: Fri, 19 May 2017 14:01:26 -0400 Message-Id: <1495216887-3175-1-git-send-email-jglisse@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Fri, 19 May 2017 16:58:30 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org After memory hot remove it seems we do not synchronize pgds for kernel virtual memory range (on vmemmap_free()). This seems bogus to me as it means we are left with stall entry for process with mm != mm_init Yet i am puzzle by the fact that i am only now hitting this issue. It never was an issue with 4.12 or before ie HMM never triggered following BUG_ON inside sync_global_pgds(): if (!p4d_none(*p4d_ref) && !p4d_none(*p4d)) BUG_ON(p4d_page_vaddr(*p4d) != p4d_page_vaddr(*p4d_ref)); It seems that Kirill 5 level page table changes play a role in this behavior change. I could not bisect because HMM is painfull to rebase for each bisection step so that is just my best guess. Am i missing something here ? Am i wrong in assuming that should sync pgd on vmemmap_free() ? If so anyone have a good guess on why i am now seeing the above BUG_ON ? Cc: Kirill A. Shutemov Cc: Andrew Morton Cc: Ingo Molnar Cc: Michal Hocko Cc: Mel Gorman Jérôme Glisse (1): x86/mm: synchronize pgd in vmemmap_free() arch/x86/mm/init_64.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) -- 2.4.11