From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-x22a.google.com (mail-wm0-x22a.google.com [IPv6:2a00:1450:400c:c09::22a]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id BD0031A0045 for ; Fri, 12 Feb 2016 06:09:47 +1100 (AEDT) Received: by mail-wm0-x22a.google.com with SMTP id c200so87726601wme.0 for ; Thu, 11 Feb 2016 11:09:47 -0800 (PST) Date: Thu, 11 Feb 2016 21:09:42 +0200 From: "Kirill A. Shutemov" To: Gerald Schaefer Cc: "Kirill A. Shutemov" , 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: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) Message-ID: <20160211190942.GA10244@node.shutemov.name> References: <20160211192223.4b517057@thinkpad> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20160211192223.4b517057@thinkpad> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, Feb 11, 2016 at 07:22:23PM +0100, Gerald Schaefer wrote: > 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. Sorry for that. I believe, the problem was already addressed for PowerPC: http://lkml.kernel.org/g/454980831-16631-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com I think kick_all_cpus_sync() in arch-specific pmdp_invalidate() would do the trick, right? If yes, I'll prepare patch tomorrow (some sleep required). -- Kirill A. Shutemov