From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754278AbcEBQee (ORCPT ); Mon, 2 May 2016 12:34:34 -0400 Received: from out4439.biz.mail.alibaba.com ([47.88.44.39]:49014 "EHLO out4439.biz.mail.alibaba.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753930AbcEBQe0 (ORCPT ); Mon, 2 May 2016 12:34:26 -0400 X-Greylist: delayed 39141 seconds by postgrey-1.27 at vger.kernel.org; Mon, 02 May 2016 12:34:26 EDT X-Alimail-AntiSpam: AC=CONTINUE;BC=0.07482303|-1;FP=0|0|0|0|0|-1|-1|-1;HT=e02c03277;MF=chengang@emindsoft.com.cn;NM=1;PH=DS;RN=8;RT=8;SR=0;TI=SMTPD_----4lBVG4X_1462206819; Message-ID: <57278294.3060006@emindsoft.com.cn> Date: Tue, 03 May 2016 00:38:44 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Alexander Potapenko CC: Dmitry Vyukov , Andrew Morton , Andrey Ryabinin , kasan-dev , LKML , "linux-mm@kvack.org" , Chen Gang Subject: Re: [PATCH] mm/kasan/kasan.h: Fix boolean checking issue for kasan_report_enabled() References: <1462167374-6321-1-git-send-email-chengang@emindsoft.com.cn> <572735EB.8030300@emindsoft.com.cn> <572747C2.5040009@emindsoft.com.cn> <57275B71.8000907@emindsoft.com.cn> <57276E95.1030201@emindsoft.com.cn> <57277EEA.6070909@emindsoft.com.cn> In-Reply-To: <57277EEA.6070909@emindsoft.com.cn> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/3/16 00:23, Chen Gang wrote: > On 5/2/16 23:35, Alexander Potapenko wrote: >> On Mon, May 2, 2016 at 5:13 PM, Chen Gang wrote: >>> >>> OK. But it does not look quite easy to use kasan_disable_current() for >>> INIT_KASAN which is used in INIT_TASK. >>> >>> If we have to set "kasan_depth == 1", we have to use kasan_depth-- in >>> kasan_enable_current(). >> Agreed, decrementing the counter in kasan_enable_current() is more natural. >> I can fix this together with the comments. > > OK, thanks. And need I also send patch v2 for include/linux/kasan.h? (or > you will fix them together). > >>> >>> If we don't prevent the overflow, it will have negative effect with the >>> caller. When we issue an warning, it means the caller's hope fail, but >>> can not destroy the caller's original work. In our case: >>> >>> - Assume "kasan_depth-- for kasan_enable_current()", the first enable >>> will let kasan_depth be 0. >> Sorry, I'm not sure I follow. >> If we start with kasan_depth=0 (which is the default case for every >> task except for the init, which also gets kasan_depth=0 short after >> the kernel starts), >> then the first call to kasan_disable_current() will make kasan_depth >> nonzero and will disable KASAN. >> The subsequent call to kasan_enable_current() will enable KASAN back. >> >> There indeed is a problem when someone calls kasan_enable_current() >> without previously calling kasan_disable_current(). >> In this case we need to check that kasan_depth was zero and print a >> warning if it was. >> It actually does not matter whether we modify kasan_depth after that >> warning or not, because we are already in inconsistent state. >> But I think we should modify kasan_depth anyway to ease the debugging. >> Oh, sorry, I forgot one of our original discussing content: - If we use signed int kasan_depth, and kasan_depth <= 0 means enable, I guess, we can always modify kasan_depth. - When overflow/underflow (singed int overflow), we can use BUG_ON(), since it should be rarely happen. Thanks. > > For me, BUG_ON() will be better for debugging, but it is really not well > for using. For WARN_ON(), it already print warnings, so I am not quite > sure "always modifying kasan_depth will be ease the debugging". > > When we are in inconsistent state, for me, what we can do is: > > - Still try to do correct things within our control: "when the caller > make a mistake, if kasan_enable_current() notices about it, it need > issue warning, and prevent itself to make mistake (causing disable). > > - "try to let negative effect smaller to user", e.g. let users "loose > hope" (call enable has no effect) instead of destroying users' > original work (call enable, but get disable). > > Thanks. > -- Chen Gang (陈刚) Managing Natural Environments is the Duty of Human Beings.