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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 6719DC433E0 for ; Thu, 4 Feb 2021 15:29:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 33FC364F43 for ; Thu, 4 Feb 2021 15:29:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237084AbhBDP3A (ORCPT ); Thu, 4 Feb 2021 10:29:00 -0500 Received: from mx2.suse.de ([195.135.220.15]:54288 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237301AbhBDP2o (ORCPT ); Thu, 4 Feb 2021 10:28:44 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 35C54ACBA; Thu, 4 Feb 2021 15:28:00 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id F1FB3DA849; Thu, 4 Feb 2021 16:26:08 +0100 (CET) Date: Thu, 4 Feb 2021 16:26:08 +0100 From: David Sterba To: ira.weiny@intel.com, clm@fb.com, josef@toxicpanda.com, dsterba@suse.com, Miao Xie , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] fs/btrfs: Fix raid6 qstripe kmap'ing Message-ID: <20210204152608.GF1993@suse.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, ira.weiny@intel.com, clm@fb.com, josef@toxicpanda.com, dsterba@suse.com, Miao Xie , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org References: <20210128061503.1496847-1-ira.weiny@intel.com> <20210203155648.GE1993@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210203155648.GE1993@suse.cz> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Feb 03, 2021 at 04:56:48PM +0100, David Sterba wrote: > On Wed, Jan 27, 2021 at 10:15:03PM -0800, ira.weiny@intel.com wrote: > > From: Ira Weiny > > > > When a qstripe is required an extra page is allocated and mapped. There > > were 3 problems. > > > > 1) There is no reason to map the qstripe page more than 1 time if the > > number of bits set in rbio->dbitmap is greater than one. > > 2) There is no reason to map the parity page and unmap it each time > > through the loop. > > 3) There is no corresponding call of kunmap() for the qstripe page. > > > > The page memory can continue to be reused with a single mapping on each > > iteration by raid6_call.gen_syndrome() without remapping. So map the > > page for the duration of the loop. > > > > Similarly, improve the algorithm by mapping the parity page just 1 time. > > > > Fixes: 5a6ac9eacb49 ("Btrfs, raid56: support parity scrub on raid56") > > To: Chris Mason > > To: Josef Bacik > > To: David Sterba > > Cc: Miao Xie > > Signed-off-by: Ira Weiny > > > > --- > > This was found while replacing kmap() with kmap_local_page(). After > > this patch unwinding all the mappings becomes pretty straight forward. > > > > I'm not exactly sure I've worded this commit message intelligently. > > Please forgive me if there is a better way to word it. > > Changelog is good, thanks. I've added stable tags as the missing unmap > is a potential problem. There are lots of tests faling, stack traces like below. I haven't seen anything obvious in the patch so that needs a closer look and for the time being I can't add the patch to for-next. BUG: kernel NULL pointer dereference, address:0000000000000000 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] PREEMPT SMP CPU: 2 PID: 17173 Comm: kworker/u8:5 Not tainted5.11.0-rc6-default+ #1422 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014 Workqueue: btrfs-rmw btrfs_work_helper [btrfs] RIP: 0010:raid6_avx22_gen_syndrome+0x103/0x140 [raid6_pq] RSP: 0018:ffffa090042cfcf8 EFLAGS: 00010246 RAX: ffff9e98e1848e80 RBX: ffff9e98d5849000 RCX:0000000000000020 RDX: ffff9e98e32be000 RSI: 0000000000000000 RDI:ffff9e98e1848e80 RBP: 0000000000000000 R08: 0000000000000000 R09:0000000000000001 R10: ffff9e98e1848e90 R11: ffff9e98e1848e98 R12:0000000000001000 R13: ffff9e98e1848e88 R14: 0000000000000005 R15:0000000000000002 FS: 0000000000000000(0000) GS:ffff9e993da00000(0000)knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 0000000023143003 CR4:0000000000170ea0 Call Trace: finish_parity_scrub+0x47b/0x7a0 [btrfs] raid56_parity_scrub_stripe+0x24e/0x260 [btrfs] btrfs_work_helper+0xd5/0x1d0 [btrfs] process_one_work+0x262/0x5f0 worker_thread+0x4e/0x300 ? process_one_work+0x5f0/0x5f0 kthread+0x151/0x170 ? __kthread_bind_mask+0x60/0x60