From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751978AbcBKSWb (ORCPT ); Thu, 11 Feb 2016 13:22:31 -0500 Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:38881 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751050AbcBKSWa (ORCPT ); Thu, 11 Feb 2016 13:22:30 -0500 X-IBM-Helo: d06dlp01.portsmouth.uk.ibm.com X-IBM-MailFrom: gerald.schaefer@de.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org;linux-s390@vger.kernel.org Date: Thu, 11 Feb 2016 19:22:23 +0100 From: Gerald Schaefer To: "Kirill A. Shutemov" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Aneesh Kumar K.V" , Andrew Morton , Linus Torvalds , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, Martin Schwidefsky , Heiko Carstens , linux-s390@vger.kernel.org, Sebastian Ott Subject: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) Message-ID: <20160211192223.4b517057@thinkpad> Organization: IBM Deutschland Research & Development GmbH / Vorsitzende des Aufsichtsrats: Martina Koederitz / Geschaeftsfuehrung: Dirk Wittkopp / Sitz der Gesellschaft: Boeblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294 X-Mailer: Claws Mail 3.9.0 (GTK+ 2.24.23; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16021118-0041-0000-0000-0000073D7DE5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Sebastian Ott reported random kernel crashes beginning with v4.5-rc1 and he also bisected this to commit 61f5d698 "mm: re-enable THP". Further review of the THP rework patches, which cannot be bisected, revealed commit fecffad "s390, thp: remove infrastructure for handling splitting PMDs" (and also similar commits for other archs). This commit removes the THP splitting bit and also the architecture implementation of pmdp_splitting_flush(), which took care of the IPI for fast_gup serialization. The commit message says pmdp_splitting_flush() is not needed too: on splitting PMD we will do pmdp_clear_flush() + set_pte_at(). pmdp_clear_flush() will do IPI as needed for fast_gup The assumption that a TLB flush will also produce an IPI is wrong on s390, and maybe also on other architectures, and I thought that this was actually the main reason for having an arch-specific pmdp_splitting_flush(). At least PowerPC and ARM also had an individual implementation of pmdp_splitting_flush() that used kick_all_cpus_sync() instead of a TLB flush to send the IPI, and those were also removed. Putting the arch maintainers and mailing lists on cc to verify. On s390 this will break the IPI serialization against fast_gup, which would certainly explain the random kernel crashes, please revert or fix the pmdp_splitting_flush() removal. Regards, Gerald