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=-2.3 required=3.0 tests=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 CE1A1C3A5A3 for ; Thu, 22 Aug 2019 12:19:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4F2A2089E for ; Thu, 22 Aug 2019 12:19:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731977AbfHVMTG (ORCPT ); Thu, 22 Aug 2019 08:19:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:33234 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727874AbfHVMTG (ORCPT ); Thu, 22 Aug 2019 08:19:06 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 39D9CAFBE; Thu, 22 Aug 2019 12:19:05 +0000 (UTC) Subject: Re: [PATCH 2/3] xfs: add kmem_alloc_io() To: Dave Chinner Cc: Peter Zijlstra , Christoph Hellwig , linux-xfs@vger.kernel.org, Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, penguin-kernel@I-love.SAKURA.ne.jp References: <20190821083820.11725-1-david@fromorbit.com> <20190821083820.11725-3-david@fromorbit.com> <20190821232440.GB24904@infradead.org> <20190822003131.GR1119@dread.disaster.area> <20190822075948.GA31346@infradead.org> <20190822085130.GI2349@hirez.programming.kicks-ass.net> <20190822091057.GK2386@hirez.programming.kicks-ass.net> <20190822101441.GY1119@dread.disaster.area> <20190822120725.GA1119@dread.disaster.area> From: Vlastimil Babka Message-ID: Date: Thu, 22 Aug 2019 14:19:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190822120725.GA1119@dread.disaster.area> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/22/19 2:07 PM, Dave Chinner wrote: > On Thu, Aug 22, 2019 at 01:14:30PM +0200, Vlastimil Babka wrote: > > No, the problem is this (using kmalloc as a general term for > allocation, whether it be kmalloc, kmem_cache_alloc, alloc_page, etc) > > some random kernel code > kmalloc(GFP_KERNEL) > reclaim > PF_MEMALLOC > shrink_slab > xfs_inode_shrink > XFS_ILOCK > xfs_buf_allocate_memory() > kmalloc(GFP_KERNEL) > > And so locks on inodes in reclaim are seen below reclaim. Then > somewhere else we have: > > some high level read-only xfs code like readdir > XFS_ILOCK > xfs_buf_allocate_memory() > kmalloc(GFP_KERNEL) > reclaim > > And this one throws false positive lockdep warnings because we > called into reclaim with XFS_ILOCK held and GFP_KERNEL alloc OK, and what exactly makes this positive a false one? Why can't it continue like the first example where reclaim leads to another XFS_ILOCK, thus deadlock? > context. So the only solution we had at the tiem to shut it up was: > > some high level read-only xfs code like readdir > XFS_ILOCK > xfs_buf_allocate_memory() > kmalloc(GFP_NOFS) > > So that lockdep sees it's not going to recurse into reclaim and > doesn't throw a warning... AFAICS that GFP_NOFS would fix not only a warning but also a real deadlock (depending on the answer to my previous question). > Cheers, > > Dave. >