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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 97CE4C3A5A7 for ; Wed, 4 Sep 2019 10:20:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7294A20449 for ; Wed, 4 Sep 2019 10:20:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729559AbfIDKUC (ORCPT ); Wed, 4 Sep 2019 06:20:02 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:56439 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725966AbfIDKUB (ORCPT ); Wed, 4 Sep 2019 06:20:01 -0400 Received: from fsav305.sakura.ne.jp (fsav305.sakura.ne.jp [153.120.85.136]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x84AJlJ4065553; Wed, 4 Sep 2019 19:19:47 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav305.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav305.sakura.ne.jp); Wed, 04 Sep 2019 19:19:47 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav305.sakura.ne.jp) Received: from [192.168.1.8] (softbank126227201116.bbtec.net [126.227.201.116]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x84AJlAg065549 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Wed, 4 Sep 2019 19:19:47 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH v3] /dev/mem: Bail out upon SIGKILL. From: Tetsuo Handa To: Greg Kroah-Hartman Cc: Arnd Bergmann , linux-kernel@vger.kernel.org, Linus Torvalds , syzbot References: <1566825205-10703-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20190826132916.GB12281@kroah.com> <87bb0adb-1d36-6481-6845-a93e5a3e5d17@i-love.sakura.ne.jp> Message-ID: <5ea28431-c677-0552-41aa-1c67779e2248@i-love.sakura.ne.jp> Date: Wed, 4 Sep 2019 19:19:47 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <87bb0adb-1d36-6481-6845-a93e5a3e5d17@i-love.sakura.ne.jp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ping? Syzbot is still reporting this problem. On 2019/08/26 22:44, Tetsuo Handa wrote: > On 2019/08/26 22:29, Greg Kroah-Hartman wrote: >> On Mon, Aug 26, 2019 at 10:13:25PM +0900, Tetsuo Handa wrote: >>> syzbot found that a thread can stall for minutes inside read_mem() or >>> write_mem() after that thread was killed by SIGKILL [1]. Reading from >>> iomem areas of /dev/mem can be slow, depending on the hardware. >>> While reading 2GB at one read() is legal, delaying termination of killed >>> thread for minutes is bad. Thus, allow reading/writing /dev/mem and >>> /dev/kmem to be preemptible and killable. >>> >>> [ 1335.912419][T20577] read_mem: sz=4096 count=2134565632 >>> [ 1335.943194][T20577] read_mem: sz=4096 count=2134561536 >>> [ 1335.978280][T20577] read_mem: sz=4096 count=2134557440 >>> [ 1336.011147][T20577] read_mem: sz=4096 count=2134553344 >>> [ 1336.041897][T20577] read_mem: sz=4096 count=2134549248 >>> >>> Theoretically, reading/writing /dev/mem and /dev/kmem can become >>> "interruptible". But this patch chose "killable". Future patch will make >>> them "interruptible" so that we can revert to "killable" if some program >>> regressed. >>> >>> [1] https://syzkaller.appspot.com/bug?id=a0e3436829698d5824231251fad9d8e998f94f5e >>> >>> Signed-off-by: Tetsuo Handa >>> Reported-by: syzbot >>> --- >>> drivers/char/mem.c | 21 +++++++++++++++++++++ >>> 1 file changed, 21 insertions(+) >> >> What changed from previous versions? >> >> That goes below the --- line at the very least. > > (1) Moved fatal_signal_pending() test to end of iteration. > (2) Added need_resched() test before cond_resched(). > (3) Removed -EINTR assignment because end of iteration means > that at least one byte was processed (sz > 0). > >> >> thanks, >> >> greg k-h >> >