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=-2.4 required=3.0 tests=DKIM_SIGNED, MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID,USER_AGENT_MUTT 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 30242C433F4 for ; Sat, 1 Sep 2018 00:32:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BB9D72083A for ; Sat, 1 Sep 2018 00:32:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="HIwL1EDO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BB9D72083A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727601AbeIAEmB (ORCPT ); Sat, 1 Sep 2018 00:42:01 -0400 Received: from mail-pg1-f194.google.com ([209.85.215.194]:37229 "EHLO mail-pg1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725988AbeIAEmB (ORCPT ); Sat, 1 Sep 2018 00:42:01 -0400 Received: by mail-pg1-f194.google.com with SMTP id 2-v6so5608556pgo.4; Fri, 31 Aug 2018 17:32:03 -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=ojr44WcL9JloHkAG32yJd+JB5DekUlgrznnwrkKSSJ0=; b=HIwL1EDOpifB9LPjiuImCUovu6gdxbO+p9an9ARPJNqoGshbDu0kLq7M1U5nbtI+jM xw97Wx1fUqg4ppq0gda9FqNeJzrRi0cIjxWkEALuD1qqbl+CXSKAQN4KIjBYmASn7KtZ V2lm2+Ss+4PSFaBRMN3hOv6T+ne3B5Bijyt3toTvkiFE5T5Ljgdqw51An4x+QU3S2k2X vy30jqTcUtXCL9HomopiwKxASpmjEQds29er0ICLgrSDMUoSWEHyZwoHLgiUoEsP+OJh X/WM9GJQmP6o4SsKqn/7YAJuzsTi7onTF5bdA9tWDVaWkyn3bWdEI182l/DOFBl2tdXx 2Wfw== 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=ojr44WcL9JloHkAG32yJd+JB5DekUlgrznnwrkKSSJ0=; b=IFqrTuZMj4UftpAtIZn6NesVNjb4dJx8lms4t+8733rDuBmxEFx8q9uHxUnqC7Rmwj De1Tcfy0ymwgQGGvHdrM3quMZSGCRX4sSH7lUBMWrKXRSuJEgZiyDWdDEs395Fnbm2X4 K1nFcCH8MLLnWtjuGnoaAM5OG26Gjf7qQ+rTAEezmIZn76ohnGX+/Jp+/ul8zBG8KTWR vRs2WBwS6ccErlMIA4dJwnPn8H+iIGPoz3ptUlSKcIJMuFZlhnBcfRH3WIqWERwQhjpF Adwr3CoHEp1GerK9H77wrPZMq16EZ/0Wae1jZP3CguZuVhHitzuE/DApb9h8nUqiILmC expw== X-Gm-Message-State: APzg51BNsXgf9GbEX2tj5zoy0FolFGaQkFcdeD+7Nj7Zn1jbNezWuboz uB1CszhcPzxuME/oQQYKvZ4= X-Google-Smtp-Source: ANB0VdYfujJyHBj4xG8JnXgZZ13Rc3owAURYwZpyxukyJd0Fe95nSJsVF01VLLwnhHyyuG2mtYSeyg== X-Received: by 2002:a63:cc04:: with SMTP id x4-v6mr16314811pgf.33.1535761923047; Fri, 31 Aug 2018 17:32:03 -0700 (PDT) Received: from localhost ([2620:10d:c090:180::1:a245]) by smtp.gmail.com with ESMTPSA id s85-v6sm19047754pfa.116.2018.08.31.17.32.01 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 31 Aug 2018 17:32:02 -0700 (PDT) Date: Fri, 31 Aug 2018 17:31:59 -0700 From: Tejun Heo To: Dennis Zhou Cc: Jens Axboe , Johannes Weiner , Josef Bacik , kernel-team@fb.com, linux-block@vger.kernel.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 13/15] blkcg: change blkg reference counting to use percpu_ref Message-ID: <20180901003159.GK1488037@devbig004.ftw2.facebook.com> References: <20180831015356.69796-1-dennisszhou@gmail.com> <20180831015356.69796-14-dennisszhou@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180831015356.69796-14-dennisszhou@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, Aug 30, 2018 at 09:53:54PM -0400, Dennis Zhou wrote: > @@ -217,6 +240,10 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, > blkg_get(blkg->parent); > } > > + ret = percpu_ref_init(&blkg->refcnt, __blkg_release, 0, GFP_KERNEL); So, while this would work in some configs, you can't depend on RCU grace period inside percpu_ref. blkg is now percpu-reference counted and rcu protected object - it has to explicitly go through a rcu grace period before release. Thanks. -- tejun