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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 503CBC433FE for ; Fri, 15 Oct 2021 13:19:26 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CD72961151 for ; Fri, 15 Oct 2021 13:19:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org CD72961151 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 4008C6B0071; Fri, 15 Oct 2021 09:19:25 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3B0286B0072; Fri, 15 Oct 2021 09:19:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 251B16B0073; Fri, 15 Oct 2021 09:19:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0253.hostedemail.com [216.40.44.253]) by kanga.kvack.org (Postfix) with ESMTP id 1740C6B0071 for ; Fri, 15 Oct 2021 09:19:25 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id C17C92FDE5 for ; Fri, 15 Oct 2021 13:19:24 +0000 (UTC) X-FDA: 78698728248.16.F0BA2D1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf10.hostedemail.com (Postfix) with ESMTP id EC2446001980 for ; Fri, 15 Oct 2021 13:19:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=xLRSIGsUfzGiK6WuxdgtdmvcVSjUeO6E6oJeq4OnRs0=; b=h2XBkXF8LeeKfvMCtxOY2LWz1O PwtQgKj1fcUO67xpNiI+6qoPqGj81MgQN6fBwGiIf9OXLpvpxtRrL+yrjULODmqnQdoD+u4ksVtTE I+eBkEC7SLHAJ5vnIAVHNBeIFUr8jiqQG0J8a7OYwiqw7qGf66e0ouuEomqkSwOG7kTJYVdk+ox2t w3lQdFrNQWFxCSdGi4I5P02SOkYK4Fs8LjOjNpeymKBvPNomKkU4GwPxD3STaelLb1QA6vjiRe2XN eJLscyae/TmjoTp069tZiQ/rn+MMi0j64iKYP1uPN+69rcH2RobmXuwo38/euYO3cCLNcEhTBtekr 2FJIpibQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mbN7G-007B1X-1j; Fri, 15 Oct 2021 13:19:18 +0000 Date: Fri, 15 Oct 2021 06:19:18 -0700 From: Christoph Hellwig To: Matthew Wilcox Cc: Zqiang , hch@infradead.org, akpm@linux-foundation.org, sunhao.th@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mikulas Patocka , Jens Axboe , Tejun Heo Subject: Re: [PATCH] mm: backing-dev: use kfree_rcu() instead of synchronize_rcu_expedited() Message-ID: References: <20211014082433.30733-1-qiang.zhang1211@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=infradead.org header.s=bombadil.20210309 header.b=h2XBkXF8; dmarc=none; spf=none (imf10.hostedemail.com: domain of BATV+717e4f5ff9d7c10515bf+6627+infradead.org+hch@bombadil.srs.infradead.org has no SPF policy when checking 198.137.202.133) smtp.mailfrom=BATV+717e4f5ff9d7c10515bf+6627+infradead.org+hch@bombadil.srs.infradead.org X-Stat-Signature: 4o9ar8op6bynuzjzhp4ng6sze6j3ed14 X-Rspamd-Queue-Id: EC2446001980 X-Rspamd-Server: rspam01 X-HE-Tag: 1634303961-588952 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Oct 15, 2021 at 01:35:56PM +0100, Matthew Wilcox wrote: > struct backing_dev_info { > u64 id; > - struct rb_node rb_node; /* keyed by ->id */ > + union { > + struct rb_node rb_node; /* keyed by ->id */ > + struct rcu_head rcu; > + }; > struct list_head bdi_list; > unsigned long ra_pages; /* max readahead in PAGE_SIZE units */ > unsigned long io_pages; /* max allowed IO size */ > > > Christoph, independent of the inode lifetime problem, this actually seems > like a good approach to take. I don't see why we should synchronize_rcu() > here? Adding Jens (original introducer of the synchronize_rcu()), Mikulas > (converted it to use _expedited) and Tejun (worked around a problem when > using _expedited). The kfree+rcu + your suggestion does seem like a good idea in general to me. But I'd still like to fix the actual bug being reported before optimizing the area in a way that papers over the bug.