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=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 E532AC2BA80 for ; Wed, 8 Apr 2020 23:14:32 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B42BC20857 for ; Wed, 8 Apr 2020 23:14:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B42BC20857 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kerneltoast.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 37E948E000D; Wed, 8 Apr 2020 19:14:32 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 32F938E0006; Wed, 8 Apr 2020 19:14:32 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 246288E000D; Wed, 8 Apr 2020 19:14:32 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0240.hostedemail.com [216.40.44.240]) by kanga.kvack.org (Postfix) with ESMTP id 09AA08E0006 for ; Wed, 8 Apr 2020 19:14:32 -0400 (EDT) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id BC4DF181AEF3C for ; Wed, 8 Apr 2020 23:14:31 +0000 (UTC) X-FDA: 76686243942.26.frogs01_61b27673daf2a X-HE-Tag: frogs01_61b27673daf2a X-Filterd-Recvd-Size: 3807 Received: from mail-pl1-f194.google.com (mail-pl1-f194.google.com [209.85.214.194]) by imf45.hostedemail.com (Postfix) with ESMTP for ; Wed, 8 Apr 2020 23:14:31 +0000 (UTC) Received: by mail-pl1-f194.google.com with SMTP id w3so3113034plz.5 for ; Wed, 08 Apr 2020 16:14:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=2dDJWh79T+QwbSORYSdxSbFbZJ+4Kb781kLYzxisEwA=; b=R1OwN6G+UV1af1W4cnPqkXGnNwcy1PWrTi9ffg7/G/LfYoJASTqd7zU6ZGnVZ9zB8j iDtb0xlwsLQcQ4WZdRDc5rBZD3vRWMG2jD9XVgRmuZ5gK+87brtXUWxr8QbZhn6if1yg VcN+XYoHtKCsZWGqYwA9L7T1pc9z/ELDzdq3lqxn7yYJ+tjCKZ/4ikdMBUj2hiJyDeW7 rf9rfBrpEfozecNSJwgCJtb4Cme1+RtG6Y4o6i8jTd3nHQr6GGfOGAj9vfT2yytwnkS/ GA0M1woOiCzhHAFH3WPOMm2UaRhQae046KVnxmrdoYer023s4aDn6nB/CucuM5ijOCAE sIRA== X-Gm-Message-State: AGi0PuYzEqwYK6f9LtfxIal5fH2PDdNdpH3uOZezLaiI1EDOC2KkewfW 1IcMb6j4kufoBedprEI1z8U= X-Google-Smtp-Source: APiQypLmMSFDOCiE+OBRFqHbxk1A6IV4TgC7GWmKe4/0VrM1zb4TXxe/3ulSYAVo/codF9ue37a8eg== X-Received: by 2002:a17:90a:8a08:: with SMTP id w8mr8213311pjn.119.1586387670316; Wed, 08 Apr 2020 16:14:30 -0700 (PDT) Received: from sultan-box.localdomain (static-198-54-129-52.cust.tzulo.com. [198.54.129.52]) by smtp.gmail.com with ESMTPSA id j5sm530256pjb.36.2020.04.08.16.14.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 16:14:29 -0700 (PDT) Date: Wed, 8 Apr 2020 16:14:25 -0700 From: Sultan Alsawaf To: Linus Torvalds Cc: "Paul E. McKenney" , Andrew Morton , Chris Wilson , David Laight , Marco Elver , Linux-MM , Mark Rutland , mm-commits@vger.kernel.org, Randy Dunlap , stable Subject: Re: [patch 125/166] lib/list: prevent compiler reloads inside 'safe' list iteration Message-ID: <20200408231425.GA2641@sultan-box.localdomain> References: <20200406200254.a69ebd9e08c4074e41ddebaf@linux-foundation.org> <20200407031042.8o-fYMox-%akpm@linux-foundation.org> <20200408202630.GA1666@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Wed, Apr 08, 2020 at 02:14:38PM -0700, Linus Torvalds wrote: > (a) what the i915 driver does is at a minimum questionable, and quite > likely actively buggy By the way, this doesn't even seem like the only place in i915 where locking and object lifetime semantics are... special. I found a combined deadlock and use-after-free last week, inside of interwoven recursive call chains, and posted a patch here [1]. Unfortunately, it's been ignored thus far. But the interesting thing is how the bizarre object lifetime semantics there required even more weird things to enact a proper fix. That patch really should be merged (Chris?), but moreover, it'd be nice to see a whole release cycle devoted to just cleaning some of this stuff up. Showstopper bugs and hangs in i915 have really multiplied in recent times. Sultan [1] https://lore.kernel.org/lkml/20200407064007.7599-1-sultan@kerneltoast.com