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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 3B659C10F11 for ; Wed, 24 Apr 2019 05:43:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0265820878 for ; Wed, 24 Apr 2019 05:43:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="sejCTUVD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729591AbfDXFnL (ORCPT ); Wed, 24 Apr 2019 01:43:11 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:44316 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726232AbfDXFnL (ORCPT ); Wed, 24 Apr 2019 01:43:11 -0400 Received: by mail-pg1-f196.google.com with SMTP id z16so4179762pgv.11 for ; Tue, 23 Apr 2019 22:43:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=6HIZTkS3Ox8iXaeKIsvQHo6rr7RP7xjOKxUXvZEMDZs=; b=sejCTUVDzsykocveLP8Mc5h43M3uPsL9O44qSiQMFXvM968FB8pYrzHMWyBCh5sDaC a9RLZdcP5r+AOXiUpj8aVmM68s/YyMQxPTWrKGOqrqx2jmN3zC/nhpIQ25wt6PrF8rRY pdWZ5dL7CZ3FolB01yeN1ztrShz7Aii+Qw5hjFTXDkSWpODVCfIkJyROySyuWOe3i0DB qkppFzhpksQMDo7fgqElDx4ITIXJ79UwNdP5jFboHCSYofxb/rTT134K58+NOYdV37An Xs2zP3ZlC429HGXP2zu7e1XcOI5LqqZ3qRJtKcDqSG+wjQyEMvTz877kmqQPhPtGZXtk 4mZg== 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:user-agent; bh=6HIZTkS3Ox8iXaeKIsvQHo6rr7RP7xjOKxUXvZEMDZs=; b=AFTnBZRDyP7C6/iI4dGlme2OgXk72tiQfL9qB9gcFsH0dYl7GP5TOuuo7AKOD0jRiP n6dugP7EX9fag6UsRKlzJvrvAB6wADGkWS0c8JtXYrx1J3+cnpb4R+lPJ5OYiBOxsHKJ AzjvevhTuDdXOdZj/4GfV8l5UPSqs7Rgg0FWCOkEvWEhs0nioaamQwf4TPulqHyf2Wr4 Am1SHpxZz6aeb/junDzZRqvgrXzeguuVsF2YTvWrznDCU2KCG5rQ3y43pinWSalYYgok DEM8UZOiszSZWWF15KQvRXE1UlspE7bC2kvJ7enuwTshRjf4nOoW7LdGhWeW1OpkMgLe ujHw== X-Gm-Message-State: APjAAAVoFOj7wBKKHATSc9gKt2i+4hmUy8rbcwzx7vAdlTFLi5vC0nbr 4I6YkRgUBjQH1F6k+3axk8wx2MnE X-Google-Smtp-Source: APXvYqwgCjmYB5yhAIxByFNRFJF47oQpEnJKaCoxklRrv9REVXh0fdRvyFoCwEU5Kb4orZWT+D6rLQ== X-Received: by 2002:a65:6656:: with SMTP id z22mr11164388pgv.333.1556084590568; Tue, 23 Apr 2019 22:43:10 -0700 (PDT) Received: from localhost ([175.223.32.169]) by smtp.gmail.com with ESMTPSA id f27sm6407193pfk.111.2019.04.23.22.43.08 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 23 Apr 2019 22:43:09 -0700 (PDT) Date: Wed, 24 Apr 2019 14:43:05 +0900 From: Sergey Senozhatsky To: Steven Rostedt Cc: Sergey Senozhatsky , Petr Mladek , Andrew Morton , linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: Re: [RFC][PATCH 0/2] Access console drivers list under console_sem Message-ID: <20190424054305.GA28894@jagdpanzerIV> References: <20190423062511.1118-1-sergey.senozhatsky@gmail.com> <20190423094801.377b8059@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190423094801.377b8059@gandalf.local.home> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (04/23/19 09:48), Steven Rostedt wrote: > > RFC > > > > Normally, we grab console_sem lock before we iterate consoles > > list, which is necessary if we want to be race free. The only exception > > to this rule is console_flush_on_panic(). However, it seems that we are > > not fully race free - register_console() iterates console drivers list > > in unsafe manner in several places. E.g. the following scenarion: > > > > CPU0 CPU1 > > register_console() unregister_console() > > console_lock() > > for_each_console() // modify console_drivers > > con->foo kfree(con) > > > > So I have two quick-n-dirty patches, which remove unsafe console list > > access. > > > > What do you think? > > I just skimmed the patches and haven't done a thorough review, but the > concept seems sane to me. Thank you Steven. Let me know if anything doesn't work for you. I have vague memories of a kernel Oops at con->foo dereferencing (saw a message on linux-rt-users list a while ago, if I'm not mistaken). And it seems that we have some races in printk code. -ss