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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 34F48C7619F for ; Mon, 17 Feb 2020 10:31:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1607420801 for ; Mon, 17 Feb 2020 10:31:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729313AbgBQKbh (ORCPT ); Mon, 17 Feb 2020 05:31:37 -0500 Received: from mx2.suse.de ([195.135.220.15]:55424 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729219AbgBQKbh (ORCPT ); Mon, 17 Feb 2020 05:31:37 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id E3D56B03E; Mon, 17 Feb 2020 10:31:35 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 3F02C1E0D47; Mon, 17 Feb 2020 11:31:35 +0100 (CET) Date: Mon, 17 Feb 2020 11:31:35 +0100 From: Jan Kara To: Shijie Luo Cc: linux-ext4@vger.kernel.org, tytso@mit.edu, jack@suse.cz, lutianxiong@huawei.com Subject: Re: [PATCH] ext4: add cond_resched() to __ext4_find_entry() Message-ID: <20200217103135.GD12032@quack2.suse.cz> References: <20200215080206.13293-1-luoshijie1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200215080206.13293-1-luoshijie1@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Sat 15-02-20 03:02:06, Shijie Luo wrote: > We tested a soft lockup problem in linux 4.19 which could also > be found in linux 5.x. > > When dir inode takes up a large number of blocks, and if the > directory is growing when we are searching, it's possible the > restart branch could be called many times, and the do while loop > could hold cpu a long time. > > Here is the call trace in linux 4.19. > > [ 473.756186] Call trace: > [ 473.756196] dump_backtrace+0x0/0x198 > [ 473.756199] show_stack+0x24/0x30 > [ 473.756205] dump_stack+0xa4/0xcc > [ 473.756210] watchdog_timer_fn+0x300/0x3e8 > [ 473.756215] __hrtimer_run_queues+0x114/0x358 > [ 473.756217] hrtimer_interrupt+0x104/0x2d8 > [ 473.756222] arch_timer_handler_virt+0x38/0x58 > [ 473.756226] handle_percpu_devid_irq+0x90/0x248 > [ 473.756231] generic_handle_irq+0x34/0x50 > [ 473.756234] __handle_domain_irq+0x68/0xc0 > [ 473.756236] gic_handle_irq+0x6c/0x150 > [ 473.756238] el1_irq+0xb8/0x140 > [ 473.756286] ext4_es_lookup_extent+0xdc/0x258 [ext4] > [ 473.756310] ext4_map_blocks+0x64/0x5c0 [ext4] > [ 473.756333] ext4_getblk+0x6c/0x1d0 [ext4] > [ 473.756356] ext4_bread_batch+0x7c/0x1f8 [ext4] > [ 473.756379] ext4_find_entry+0x124/0x3f8 [ext4] > [ 473.756402] ext4_lookup+0x8c/0x258 [ext4] > [ 473.756407] __lookup_hash+0x8c/0xe8 > [ 473.756411] filename_create+0xa0/0x170 > [ 473.756413] do_mkdirat+0x6c/0x140 > [ 473.756415] __arm64_sys_mkdirat+0x28/0x38 > [ 473.756419] el0_svc_common+0x78/0x130 > [ 473.756421] el0_svc_handler+0x38/0x78 > [ 473.756423] el0_svc+0x8/0xc > [ 485.755156] watchdog: BUG: soft lockup - CPU#2 stuck for 22s! [tmp:5149] > > Add cond_resched() to avoid soft lockup and to provide a better > system responding. > > Signed-off-by: Shijie Luo Thanks for the patch! It looks good. You can add: Reviewed-by: Jan Kara I was just wondering how come we didn't hit other scheduling points (e.g. when reading directory blocks from the disk) but likely the directory including new blocks was staying in cache... Honza > --- > fs/ext4/namei.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c > index 129d2ebae00d..9a1836632f51 100644 > --- a/fs/ext4/namei.c > +++ b/fs/ext4/namei.c > @@ -1511,6 +1511,7 @@ static struct buffer_head *__ext4_find_entry(struct inode *dir, > /* > * We deal with the read-ahead logic here. > */ > + cond_resched(); > if (ra_ptr >= ra_max) { > /* Refill the readahead buffer */ > ra_ptr = 0; > -- > 2.19.1 > -- Jan Kara SUSE Labs, CR