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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 A4AA2C3A5A2 for ; Tue, 3 Sep 2019 20:53:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 797B6208E4 for ; Tue, 3 Sep 2019 20:53:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="q6PKtm2q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726810AbfICUxQ (ORCPT ); Tue, 3 Sep 2019 16:53:16 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:39632 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726005AbfICUxQ (ORCPT ); Tue, 3 Sep 2019 16:53:16 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=9j9Ys3SKrunuUdWnpddWrlF3hlzVX+dYskTpGsMVRdg=; b=q6PKtm2qHXC4ZxDd1oWAesGqt mkef31ksS0DE/m+V94xxk8mY4E4NK7/D6yceAd4IMOYEtng6UUMmitBiFDXkmyC3VsZShsSIDhDxA spbPZghZh0gaSPUEaq9m2Id0riRmEJzPcniu1pE5CxkkCA32WDRJ3NzR/05hgewKmdlszxQcADztH z19osbBcPHxeseNqIEdEFRXQ1AGIdZ5S6kJBEUtzqgvVeooolY2oxTjjKG+adYErsSQPK+86v+0qP AK7u61q/Rmd8W04N+VU/Ik4OalyMQ207Yu/0eA5EaNXbWRdvGCZGHdJNie5vvkiHaECkD4l0efUVb n2xH0iMQA==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1i5Fnc-0005w9-SY; Tue, 03 Sep 2019 20:53:12 +0000 Date: Tue, 3 Sep 2019 13:53:12 -0700 From: Matthew Wilcox To: Christopher Lameter Cc: Michal Hocko , Vlastimil Babka , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pekka Enberg , David Rientjes , Ming Lei , Dave Chinner , "Darrick J . Wong" , Christoph Hellwig , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, James Bottomley , linux-btrfs@vger.kernel.org Subject: Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two) Message-ID: <20190903205312.GK29434@bombadil.infradead.org> References: <20190826111627.7505-1-vbabka@suse.cz> <20190826111627.7505-3-vbabka@suse.cz> <0100016cd98bb2c1-a2af7539-706f-47ba-a68e-5f6a91f2f495-000000@email.amazonses.com> <20190828194607.GB6590@bombadil.infradead.org> <20190829073921.GA21880@dhcp22.suse.cz> <0100016ce39e6bb9-ad20e033-f3f4-4e6d-85d6-87e7d07823ae-000000@email.amazonses.com> <20190901005205.GA2431@bombadil.infradead.org> <0100016cf8c3033d-bbcc9ba3-2d59-4654-a7c2-8ba094f8a7de-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0100016cf8c3033d-bbcc9ba3-2d59-4654-a7c2-8ba094f8a7de-000000@email.amazonses.com> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Sep 03, 2019 at 08:13:45PM +0000, Christopher Lameter wrote: > On Sat, 31 Aug 2019, Matthew Wilcox wrote: > > > > The current behavior without special alignment for these caches has been > > > in the wild for over a decade. And this is now coming up? > > > > In the wild ... and rarely enabled. When it is enabled, it may or may > > not be noticed as data corruption, or tripping other debugging asserts. > > Users then turn off the rare debugging option. > > Its enabled in all full debug session as far as I know. Fedora for > example has been running this for ages to find breakage in device drivers > etc etc. Are you telling me nobody uses the ramdisk driver on fedora? Because that's one of the affected drivers. > > > If there is an exceptional alignment requirement then that needs to be > > > communicated to the allocator. A special flag or create a special > > > kmem_cache or something. > > > > The only way I'd agree to that is if we deliberately misalign every > > allocation that doesn't have this special flag set. Because right now, > > breakage happens everywhere when these debug options are enabled, and > > the very people who need to be helped are being hurt by the debugging. > > That is customarily occurring for testing by adding "slub_debug" to the > kernel commandline (or adding debug kernel options) and since my > information is that this is done frequently (and has been for over a > decade now) I am having a hard time believing the stories of great > breakage here. These drivers were not tested with debugging on before? > Never ran with a debug kernel? Whatever is being done is clearly not enough to trigger the bug. So how about it? Create an option to slab/slub to always return misaligned memory.