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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 90EEAFA3728 for ; Wed, 16 Oct 2019 13:49:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6CAF62168B for ; Wed, 16 Oct 2019 13:49:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405518AbfJPNtv (ORCPT ); Wed, 16 Oct 2019 09:49:51 -0400 Received: from mx2.suse.de ([195.135.220.15]:47290 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726689AbfJPNtu (ORCPT ); Wed, 16 Oct 2019 09:49:50 -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 06EF3BC0E; Wed, 16 Oct 2019 13:49:49 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 3DBDD1E4360; Wed, 16 Oct 2019 15:49:45 +0200 (CEST) Date: Wed, 16 Oct 2019 15:49:45 +0200 From: Jan Kara To: Eric Sandeen Cc: Jan Kara , Eric Sandeen , fsdevel , Al Viro Subject: Re: [PATCH V2] fs: avoid softlockups in s_inodes iterators Message-ID: <20191016134945.GD7198@quack2.suse.cz> References: <20191015073740.GA21550@quack2.suse.cz> <20191016094237.GE30337@quack2.suse.cz> <3a175c93-d7b2-5afb-fc2c-69951eb17838@sandeen.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3a175c93-d7b2-5afb-fc2c-69951eb17838@sandeen.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed 16-10-19 08:23:51, Eric Sandeen wrote: > On 10/16/19 4:42 AM, Jan Kara wrote: > > On Tue 15-10-19 21:36:08, Eric Sandeen wrote: > >> On 10/15/19 2:37 AM, Jan Kara wrote: > >>> On Mon 14-10-19 16:30:24, Eric Sandeen wrote: > >>>> Anything that walks all inodes on sb->s_inodes list without rescheduling > >>>> risks softlockups. > >>>> > >>>> Previous efforts were made in 2 functions, see: > >>>> > >>>> c27d82f fs/drop_caches.c: avoid softlockups in drop_pagecache_sb() > >>>> ac05fbb inode: don't softlockup when evicting inodes > >>>> > >>>> but there hasn't been an audit of all walkers, so do that now. This > >>>> also consistently moves the cond_resched() calls to the bottom of each > >>>> loop in cases where it already exists. > >>>> > >>>> One loop remains: remove_dquot_ref(), because I'm not quite sure how > >>>> to deal with that one w/o taking the i_lock. > >>>> > >>>> Signed-off-by: Eric Sandeen > >>> > >>> Thanks Eric. The patch looks good to me. You can add: > >>> > >>> Reviewed-by: Jan Kara > >> > >> thanks > >> > >>> BTW, I suppose you need to add Al to pickup the patch? > >> > >> Yeah (cc'd now) > >> > >> But it was just pointed out to me that if/when the majority of inodes > >> at umount time have i_count == 0, we'll never hit the resched in > >> fsnotify_unmount_inodes() and may still have an issue ... > > > > Yeah, that's a good point. So that loop will need some further tweaking > > (like doing iget-iput dance in need_resched() case like in some other > > places). > > Well, it's already got an iget/iput for anything with i_count > 0. But > as the comment says (and I think it's right...) doing an iget/iput > on i_count == 0 inodes at this point would be without SB_ACTIVE and the final > iput here would actually start evicting inodes in /this/ loop, right? Yes, it would but since this is just before calling evict_inodes(), I have currently hard time remembering why evicting inodes like that would be an issue. > I think we could (ab)use the lru list to construct a "dispose" list for > fsnotify processing as was done in evict_inodes... > > or maybe the two should be merged, and fsnotify watches could be handled > directly in evict_inodes. But that doesn't feel quite right. Merging the two would be possible (and faster!) as well but I agree it feels a bit dirty :) Honza -- Jan Kara SUSE Labs, CR