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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 C5C3BC10F14 for ; Tue, 23 Apr 2019 13:48:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 99A0A217D9 for ; Tue, 23 Apr 2019 13:48:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727857AbfDWNsE (ORCPT ); Tue, 23 Apr 2019 09:48:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:34648 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726659AbfDWNsE (ORCPT ); Tue, 23 Apr 2019 09:48:04 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0630D21773; Tue, 23 Apr 2019 13:48:02 +0000 (UTC) Date: Tue, 23 Apr 2019 09:48:01 -0400 From: Steven Rostedt To: Sergey Senozhatsky Cc: 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: <20190423094801.377b8059@gandalf.local.home> In-Reply-To: <20190423062511.1118-1-sergey.senozhatsky@gmail.com> References: <20190423062511.1118-1-sergey.senozhatsky@gmail.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 23 Apr 2019 15:25:09 +0900 Sergey Senozhatsky wrote: > Petr, Steven, > > 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. -- Steve > > Sergey Senozhatsky (2): > printk: lock console_sem before we unregister boot consoles > printk: take console_sem when accessing console drivers list > > kernel/printk/printk.c | 117 ++++++++++++++++++++++++----------------- > 1 file changed, 69 insertions(+), 48 deletions(-) >