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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 643F4C3A589 for ; Thu, 15 Aug 2019 16:12:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3921C2083B for ; Thu, 15 Aug 2019 16:12:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565885540; bh=Kb2LiuIF1S/oXcqeHW1qMfCRG37dm3QbSZje55wpusU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=M+s9zHPTA6Ve0A+SJjTCd6uhPTPpaMFae6F7UCbsQw9gyNXL4JjglwSVYF8ibE83c 9OsS7ODtxvpWBANjD6eWpK3dZVTdffkGe8D1+o+Q9Cpn5rG0g/23GM5A/e84iTCnv6 0EVc6titMXCX+mR37iRzHVPMkdDC1CLL+fXmw980= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729565AbfHOQMP (ORCPT ); Thu, 15 Aug 2019 12:12:15 -0400 Received: from mail-qt1-f194.google.com ([209.85.160.194]:42095 "EHLO mail-qt1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729151AbfHOQMP (ORCPT ); Thu, 15 Aug 2019 12:12:15 -0400 Received: by mail-qt1-f194.google.com with SMTP id t12so2870936qtp.9; Thu, 15 Aug 2019 09:12:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=iTIKIuhQjFmLzffUqNs0d7EM6m2UJCFz471NWYlW/kA=; b=QXjkEAHzvaI4d+a1jTu1uuBdBcwkiUcidF6xSV/xQKF2N7ucXBCF5Hej38FIPF0Lm3 9fWE+N6hf68OLIhzBONo5J5LQOEGzbqPKECQp+aEdwFdT+opMpMJ1qGxqzQD9gdQCPEz IecizOukDzYwhTyD2KWejogmiAgKaK1vXPLIaF4L9biBH+TFPKprcr2WQ/6fGoTrK2rx p6Un0uytpeqSTUTd8k+dvepjTTMJOAFXt4wObsUiZTFbAJFHR3q+4a3Y/b8ZvK/foXDm wpA60ZcOdP6GWCrYCNX13gHb4P/T2mGkfQelkmBGCL+lGa6+8NnbqBd7hYAfkgZPkPEV CS9w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=iTIKIuhQjFmLzffUqNs0d7EM6m2UJCFz471NWYlW/kA=; b=DshGSZyBDDUsy6n0MdXUVPNma+jMuvlxlFrUV5h7A9AeJz9Nevh/ZRjX1hRnWsoQqH IVWDB/OOyqs4n6nDeuPap1i8UtdE2uYP+dLnKlQ1Xr441meYWrUunrkQWVpAfLuCRCik ysGyKelbR2Np/zJErNvm+FlR+Hcmd4XHpR/TRH42oSODMXVfblXvsi9HB5bSndgKjmha 50lydEXjH0Z0psxIc2rcs4qwha8eQN0v0sbzHigXyDe0dP8FCz3VHOpUwSMtcJ+F8Uh3 QU7OzYGkmU63aNRi2LO7hsLy4uEvEqp8R6koRceXbbZjFCYSk2rkt8Abf13ht5NHCfbZ hQUQ== X-Gm-Message-State: APjAAAVjqL2yviom4OtbQgwb1fO41o+JVXMkiLziG0MbPcXRrU1+WCEW n4uFlrdt8aMdJhR77Ppp2DI= X-Google-Smtp-Source: APXvYqyI+etnk5089VErOMk8XqgTxfwAkSptHHANrHUw1yrHJeZLiH5w0UkWbcFYiSOmm16KjfaZlA== X-Received: by 2002:ac8:6b8f:: with SMTP id z15mr4797796qts.62.1565885534276; Thu, 15 Aug 2019 09:12:14 -0700 (PDT) Received: from localhost ([2620:10d:c091:500::1:25cd]) by smtp.gmail.com with ESMTPSA id a21sm1430581qtj.5.2019.08.15.09.12.13 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 15 Aug 2019 09:12:13 -0700 (PDT) Date: Thu, 15 Aug 2019 09:12:11 -0700 From: Tejun Heo To: Jan Kara Cc: axboe@kernel.dk, hannes@cmpxchg.org, mhocko@kernel.org, vdavydov.dev@gmail.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, guro@fb.com, akpm@linux-foundation.org Subject: Re: [PATCH 3/4] writeback, memcg: Implement cgroup_writeback_by_id() Message-ID: <20190815161211.GC588936@devbig004.ftw2.facebook.com> References: <20190803140155.181190-1-tj@kernel.org> <20190803140155.181190-4-tj@kernel.org> <20190815145421.GN14313@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190815145421.GN14313@quack2.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Aug 15, 2019 at 04:54:21PM +0200, Jan Kara wrote: > > + /* and find the associated wb */ > > + wb = wb_get_create(bdi, memcg_css, GFP_NOWAIT | __GFP_NOWARN); > > + if (!wb) { > > + ret = -ENOMEM; > > + goto out_css_put; > > + } > > One more thought: You don't want the "_create" part here, do you? If > there's any point in writing back using this wb, it must be attached to > some inode and thus it must exist. In the normal case wb_get_create() will > just fetch the reference and be done with it but when you feed garbage into > this function due to id going stale or frn structures getting corrupted due > to concurrent access, you can be creating bogus wb structures in bdi... Yeah, it can create wbs unnecessarily which isn't critical but also is easy to fix. Will update. Thanks. -- tejun