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,URIBL_BLOCKED, 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 71C25C3A59F for ; Mon, 26 Aug 2019 13:44:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4E169206B7 for ; Mon, 26 Aug 2019 13:44:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732022AbfHZNoq (ORCPT ); Mon, 26 Aug 2019 09:44:46 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:62781 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731954AbfHZNop (ORCPT ); Mon, 26 Aug 2019 09:44:45 -0400 Received: from fsav106.sakura.ne.jp (fsav106.sakura.ne.jp [27.133.134.233]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x7QDiXgm019577; Mon, 26 Aug 2019 22:44:33 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav106.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav106.sakura.ne.jp); Mon, 26 Aug 2019 22:44:33 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav106.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 x7QDiXGe019573 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Mon, 26 Aug 2019 22:44:33 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH v3] /dev/mem: Bail out upon SIGKILL. 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> From: Tetsuo Handa Message-ID: <87bb0adb-1d36-6481-6845-a93e5a3e5d17@i-love.sakura.ne.jp> Date: Mon, 26 Aug 2019 22:44:29 +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: <20190826132916.GB12281@kroah.com> 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 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 >