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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 63050C4332F for ; Fri, 8 Apr 2022 04:10:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BD34A6B0071; Fri, 8 Apr 2022 00:10:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B832B6B0072; Fri, 8 Apr 2022 00:10:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A4A186B0074; Fri, 8 Apr 2022 00:10:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (relay.a.hostedemail.com [64.99.140.24]) by kanga.kvack.org (Postfix) with ESMTP id 958AF6B0071 for ; Fri, 8 Apr 2022 00:10:21 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 65178213A5 for ; Fri, 8 Apr 2022 04:10:21 +0000 (UTC) X-FDA: 79332384642.10.97F863F Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf17.hostedemail.com (Postfix) with ESMTP id D057640002 for ; Fri, 8 Apr 2022 04:10:20 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 2259B61E1E; Fri, 8 Apr 2022 04:10:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3FB25C385A1; Fri, 8 Apr 2022 04:10:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1649391019; bh=a5MW3Y7fTlcWfiSqExChn/gvYPyz15/eSD1A/kNQLm0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=jnPukCRDuNYENUubVhda6jWGi7qBKt0mxnQsXPSIMC+ZMY06KlwQ589fj7QryLIqK ATQuvXlavifEXziVeRPHpx4/0N4I4TXp3iamCj8HM+zjmRP8crl90cZyPC4s0RSFW9 OmkHz4Z/CkX5ZT64tB/BJb7ngw5LfOcXxP4wpTcU= Date: Thu, 7 Apr 2022 21:10:18 -0700 From: Andrew Morton To: Qi Zheng Cc: Muchun Song , dennis@kernel.org, tj@kernel.org, cl@linux.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, zhouchengming@bytedance.com Subject: Re: [PATCH] percpu_ref: call wake_up_all() after percpu_ref_put() completes Message-Id: <20220407211018.875696691e4411a7b5c8f63f@linux-foundation.org> In-Reply-To: <35195a61-d531-aeb2-5565-146e345f8bf6@bytedance.com> References: <20220407103335.36885-1-zhengqi.arch@bytedance.com> <20220407205419.f656419a8f4665a2dc781133@linux-foundation.org> <35195a61-d531-aeb2-5565-146e345f8bf6@bytedance.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 4rxj6hgaagtm1rfswwp71f7718sx9sg8 Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=jnPukCRD; spf=pass (imf17.hostedemail.com: domain of akpm@linux-foundation.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: D057640002 X-HE-Tag: 1649391020-225514 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000060, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, 8 Apr 2022 12:06:20 +0800 Qi Zheng wrote: > > > >>>> Signed-off-by: Qi Zheng > >>> > >>> Are any users affected by this? If so, I think a Fixes tag > >>> is necessary. > >> > >> Looks all current users(blk_pre_runtime_suspend() and set_in_sync()) are > >> affected by this. > >> > >> I see that this patch has been merged into the mm tree, can Andrew help > >> me add the following Fixes tag? > > > > Andrew is helpful ;) > > > > Do you see reasons why we should backport this into -stable trees? > > It's 8 years old, so my uninformed guess is "no"? > > Hmm, although the commit 490c79a65708 add wake_up_all(), it is no > problem for the usage at that time, maybe the correct Fixes tag is the > following: > > Fixes: 210f7cdcf088 ("percpu-refcount: support synchronous switch to > atomic mode.") > > But in fact, there is no problem with it, but all current users expect > the refcount is stable after percpu_ref_switch_to_atomic_sync() returns. > > I have no idea as which Fixes tag to add. Well the solution to that problem is to add cc:stable and let Greg figure it out ;) The more serious question is "should we backport this". What is the end-user-visible impact of the bug? Do our users need the fix or not?