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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E2C4DC27C75 for ; Tue, 11 Jun 2024 17:24:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=8SRt+69rZERIMH5luSM3/A2HTfJLQVNOydoDukUqqaw=; b=H46ubQq0EXk5CPC8BGRO7hq7A2 iMx4lgN414dmdD2/6kfv8iEwrrBb+cA8vml6Y4kDrB7SSvg7D0H3HPPhaO4Hk4JmrtZMVklSB+jAf +xmA6BL/3YsQtyKBV5aTun7eKmkOzePBjLoq85BaF5o2rumz3pKbIOhkNHllUpGwofvkGeJEvJKc8 p4wmgF9zHgXSpwqT2ezGgMfQiED8LEWlRlC74rfnXSvM0X8/dMqeygkMhta/K1DbrNMiwHce86HIY KSniPR9o2t0DfvJiZvEyT1wJSwLp0yJ8xL/1XxeuGBEahnFbqU+5vxqlMgDVealMxoYUL5a1hEoDw /FwxOHEw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sH5Ex-00000009fBG-1Fpp; Tue, 11 Jun 2024 17:24:59 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sH5Es-00000009f7f-1Dgp for linux-nvme@lists.infradead.org; Tue, 11 Jun 2024 17:24:57 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id AAAE868BEB; Tue, 11 Jun 2024 19:24:48 +0200 (CEST) Date: Tue, 11 Jun 2024 19:24:48 +0200 From: Christoph Hellwig To: Keith Busch Cc: Christoph Hellwig , Keith Busch , linux-nvme@lists.infradead.org, sagi@grimberg.me, Venkat Rao Bagalkote , "Paul E. McKenney" , rcu@vger.kernel.org Subject: Re: [PATCH] nvme: fix namespace removal list Message-ID: <20240611172448.GA13680@lst.de> References: <20240611152055.2317197-1-kbusch@meta.com> <20240611163955.GA12787@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240611_102454_549057_B0324BFD X-CRM114-Status: GOOD ( 22.50 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Tue, Jun 11, 2024 at 11:22:04AM -0600, Keith Busch wrote: > > Is this actually valid for a (S)RCU protected list? If the entry gets > > added to the new list before the grace period has completed, we could > > trick a concurrent traversal into following the new list unless I'm > > mistaken (although chances I'm mistaken on RCU corner cases aren't that > > low..). > > Good call, you are absolutely right that a sync should happen between > the del and the add for readers to consistently iterate this list. > > I might be able to weasel out of this though: our namespace list is > sorted, and this function wants to append everything from this element > all the way to the end to the "rm_list": a reader should get the same > result either way, whether if it was torn at this element or the move > happened without the reader seeing it. > > Now if there was a way to rcu split the list so we don't have to do it > element by element... Isn't that exactly what the list_splice helpers do? We'd just need to do that exactly once at the cutoff point and not once per namespace.