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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 D035EC2BB1D for ; Thu, 12 Mar 2020 00:59:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D694E20737 for ; Thu, 12 Mar 2020 00:59:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583974762; bh=JABgZCHmEBb3tn/P9d99r9kBtaxONATZlzJZzI6/7h4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=qp2fpSh5hztmJe+pVQ4rB3ugH+PlZY923l2g78N+scXT5MWfpSa12c6Fj1mj2T/8x Sp7lLqxA6zaNhiZGBoNtF5KLUklkyIhlqUzlZfhMK9Z+sosWP3cVnyUwEGti199R79 N/JFfwOSKkljB+gcYzAwJFNcmB3hs9yPF3Q87QqE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387603AbgCLA7V (ORCPT ); Wed, 11 Mar 2020 20:59:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:39002 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387518AbgCLA7V (ORCPT ); Wed, 11 Mar 2020 20:59:21 -0400 Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7B0D520734; Thu, 12 Mar 2020 00:59:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1583974760; bh=JABgZCHmEBb3tn/P9d99r9kBtaxONATZlzJZzI6/7h4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=dljkngR2apT/UPuwBHxo/d8Tb+tarA2I5DfIGV5mm0seMImzOdeOOyzU3ZheyPq4B mzK2fcyoCMlaF9y1ccJ5JxNstj7+bz3gA4xqrc7sVXAMGPrELUUNEIf9hLVaW+Ocer SJ0ooQgN9AgmmZ6r2ObKEfsiuWWZ2xP5MyamOCmI= Date: Wed, 11 Mar 2020 17:59:19 -0700 From: Andrew Morton To: Jules Irenge Cc: boqun.feng@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] backing-dev: refactor wb_congested_put() Message-Id: <20200311175919.30523d55b2e5307ba22bbdc0@linux-foundation.org> In-Reply-To: <20200312002156.49023-2-jbi.octave@gmail.com> References: <20200312002156.49023-1-jbi.octave@gmail.com> <20200312002156.49023-2-jbi.octave@gmail.com> X-Mailer: Sylpheed 3.5.1 (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 Thu, 12 Mar 2020 00:21:56 +0000 Jules Irenge wrote: > wb_congested_put() was written in such a way that made it difficult > for Sparse tool not to complain > Expanding the function locking block in the if statement improves on > the readability of the code. Rewritting it comes with one add-on: > > It fixes a warning reported by Sparse tool at wb_congested_put() > > warning: context imbalance in wb_congested_put() - unexpected unlock > > Refactor the function wb_congested_put() > > ... > > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -464,18 +464,21 @@ void wb_congested_put(struct bdi_writeback_congested *congested) > { > unsigned long flags; > > - if (!refcount_dec_and_lock_irqsave(&congested->refcnt, &cgwb_lock, &flags)) > - return; > - > + if (!refcount_dec_not_one(&congested->refcnt)) { > + spin_lock_irqsave(&cgwb_lock, flags); > + if (!refcount_dec_and_test(&congested->refcnt)) { > + spin_unlock_irqrestore(&cgwb_lock, flags); > + return; > + } > /* bdi might already have been destroyed leaving @congested unlinked */ > - if (congested->__bdi) { > - rb_erase(&congested->rb_node, > - &congested->__bdi->cgwb_congested_tree); > - congested->__bdi = NULL; > + if (congested->__bdi) { > + rb_erase(&congested->rb_node, > + &congested->__bdi->cgwb_congested_tree); > + congested->__bdi = NULL; > + } > + spin_unlock_irqrestore(&cgwb_lock, flags); > + kfree(congested); > } > - > - spin_unlock_irqrestore(&cgwb_lock, flags); > - kfree(congested); > } hm, it's hard to get excited over this. Open-coding the refcount_dec_and_lock_irqsave() internals at a callsite in order to make sparse happy. Is there some other way, using __acquires (for example)?