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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 80FB5C4332F for ; Mon, 12 Dec 2022 06:23:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231311AbiLLGXz (ORCPT ); Mon, 12 Dec 2022 01:23:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37758 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229726AbiLLGXw (ORCPT ); Mon, 12 Dec 2022 01:23:52 -0500 Received: from mail-pj1-x1030.google.com (mail-pj1-x1030.google.com [IPv6:2607:f8b0:4864:20::1030]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE0A3B845 for ; Sun, 11 Dec 2022 22:23:51 -0800 (PST) Received: by mail-pj1-x1030.google.com with SMTP id js9so9917245pjb.2 for ; Sun, 11 Dec 2022 22:23:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:from:to:cc:subject:date:message-id :reply-to; bh=16qjFjVCSByPSmaTuD6/Rn3kPnlB8HVnWQrOiENDUnQ=; b=i9Z0r6NITq9TRj+RUGURJbxiHaklMCriP5vPoXMX1iq0ZiQUewgeuwqnS+moJb1Pxb aKaM5fiqklCwGLtJoqWAlSKTPQML5vV18ez36qWb/FJQKXNlr3ooSmnYxRL3I7sQz2Q5 Mqa5Sy5ZB3x5aFnQBy2UL9Kwby2+bmzGxQpf6heIA3AizBdIwqNzh3aN6KQk4dtJthN7 0sxax/K5xH3wOkQ7b7o7pFlUCXBBgxiuBBY7bwgx6+fqHSnkoRZxiP+uuF2s1bFu0/9p 0FbW4W5JUODSa5Hz2fuorIC/M5sHPmcUHhIRaoc75q1SnTe6rAMeROBlUC6pYlujVNUI ewyw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=16qjFjVCSByPSmaTuD6/Rn3kPnlB8HVnWQrOiENDUnQ=; b=iqvEtOPIjZCkML/3neujdi6+1kp7GWybjQnaF63fw4xmI+8CCvfpTudNr8Enr8r9Jb M8/EvTAU1vdfMGnsHC4qkAv9CSLxUfqhfQ8jDcCB3Jw4NY6sB/+v54Kd5T+YCVxLKVE6 A87Gjmks++gPXAZl0fwg2mne0jCSAQWmakvus7Yv6dVC8e91vQQ+VSHlccdt8/eupzq4 8TTk1vWpHBko5x/QUPZnBd+EEu+m1kUP8mZx7e/f+deAWhR55zVdwM6kox9QwwByEYZv R/Gk71OpdSrlMfy2iy4K0Muj+e6Nyb1V+jr3P/abA92Lty2W/J2Ipqs6UNd/zVpUR4V2 JaOA== X-Gm-Message-State: ANoB5plJZeMpyPLRALp/h5c0rxirA2QXnXeU9WQNUX7+qktQtduVPsET WgxB1wYg51Ua8xgCKH7cSVV++VzqzxMizQ== X-Google-Smtp-Source: AA0mqf7BcvB/V0ijOniyMqhsVQqV3Fi4laAk2txZkZMuFZcjghgl6Ff663EKYGi92pEfcajCcOwbwA== X-Received: by 2002:a17:902:930a:b0:188:da5c:152b with SMTP id bc10-20020a170902930a00b00188da5c152bmr14515056plb.9.1670826231221; Sun, 11 Dec 2022 22:23:51 -0800 (PST) Received: from localhost ([2620:10d:c090:400::5:9159]) by smtp.gmail.com with ESMTPSA id s17-20020a170902ea1100b00189c26719cdsm5375734plg.272.2022.12.11.22.23.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 11 Dec 2022 22:23:50 -0800 (PST) Sender: Tejun Heo Date: Sun, 11 Dec 2022 20:23:49 -1000 From: Tejun Heo To: Richard Clark Cc: jiangshanlai@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] workqueue: Prevent a new work item from queueing into a destruction wq Message-ID: References: <20221212061836.3620-1-richard.xnu.clark@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221212061836.3620-1-richard.xnu.clark@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 12, 2022 at 02:18:36PM +0800, Richard Clark wrote: > Currently the __WQ_DRAINING is used to prevent a new work item from queueing > to a draining workqueue, but this flag will be cleared before the end of a > RCU grace period. Because the workqueue instance is actually freed after > the RCU grace period, this fact results in an opening window in which a new > work item can be queued into a destorying workqueue and be scheduled > consequently, for instance, the below code snippet demos this accident: I mean, this is just use-after-free. The same scenario can happen with non-RCU frees or if there happens to be an RCU grace period inbetween. I'm not sure what's being protected here. Thanks. -- tejun