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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 4B625ECDFB3 for ; Mon, 16 Jul 2018 22:57:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F2F0220862 for ; Mon, 16 Jul 2018 22:57:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F2F0220862 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.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 S1729808AbeGPX0v (ORCPT ); Mon, 16 Jul 2018 19:26:51 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:41122 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728947AbeGPX0v (ORCPT ); Mon, 16 Jul 2018 19:26:51 -0400 Received: from akpm3.svl.corp.google.com (unknown [104.133.9.92]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id C1532BE1; Mon, 16 Jul 2018 22:57:17 +0000 (UTC) Date: Mon, 16 Jul 2018 15:57:16 -0700 From: Andrew Morton To: Sebastian Andrzej Siewior Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, Peter Zijlstra , Ingo Molnar , linux-mm@kvack.org, Jens Axboe Subject: Re: [PATCH 3/6] bdi: Use refcount_t for reference counting instead atomic_t Message-Id: <20180716155716.1f7ac43d211133a8cb476637@linux-foundation.org> In-Reply-To: <20180703200141.28415-4-bigeasy@linutronix.de> References: <20180703200141.28415-1-bigeasy@linutronix.de> <20180703200141.28415-4-bigeasy@linutronix.de> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 3 Jul 2018 22:01:38 +0200 Sebastian Andrzej Siewior wrote: > refcount_t type and corresponding API should be used instead of atomic_t when > the variable is used as a reference counter. This allows to avoid accidental > refcounter overflows that might lead to use-after-free situations. > > ... > > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -438,10 +438,10 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp) > if (new_congested) { > /* !found and storage for new one already allocated, insert */ > congested = new_congested; > - new_congested = NULL; > rb_link_node(&congested->rb_node, parent, node); > rb_insert_color(&congested->rb_node, &bdi->cgwb_congested_tree); > - goto found; > + spin_unlock_irqrestore(&cgwb_lock, flags); > + return congested; > } > > spin_unlock_irqrestore(&cgwb_lock, flags); > @@ -451,13 +451,13 @@ wb_congested_get_create(struct backing_dev_info *bdi, int blkcg_id, gfp_t gfp) > if (!new_congested) > return NULL; > > - atomic_set(&new_congested->refcnt, 0); > + refcount_set(&new_congested->refcnt, 1); > new_congested->__bdi = bdi; > new_congested->blkcg_id = blkcg_id; > goto retry; > > found: > - atomic_inc(&congested->refcnt); > + refcount_inc(&congested->refcnt); > spin_unlock_irqrestore(&cgwb_lock, flags); > kfree(new_congested); > return congested; > > ... > I'm not sure that the restructuring of wb_congested_get_create() was desirable and it does make the patch harder to review. But it looks OK to me.