From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f72.google.com (mail-pa0-f72.google.com [209.85.220.72]) by kanga.kvack.org (Postfix) with ESMTP id 2FB5C6B007E for ; Mon, 2 May 2016 12:33:57 -0400 (EDT) Received: by mail-pa0-f72.google.com with SMTP id zy2so301501376pac.1 for ; Mon, 02 May 2016 09:33:57 -0700 (PDT) Received: from out4435.biz.mail.alibaba.com (out4435.biz.mail.alibaba.com. [47.88.44.35]) by mx.google.com with ESMTP id lx17si38218915pab.66.2016.05.02.09.33.55 for ; Mon, 02 May 2016 09:33:56 -0700 (PDT) Message-ID: <57278294.3060006@emindsoft.com.cn> Date: Tue, 03 May 2016 00:38:44 +0800 From: Chen Gang MIME-Version: 1.0 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: owner-linux-mm@kvack.org List-ID: To: Alexander Potapenko Cc: Dmitry Vyukov , Andrew Morton , Andrey Ryabinin , kasan-dev , LKML , "linux-mm@kvack.org" , Chen Gang 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 (e??a??) Managing Natural Environments is the Duty of Human Beings. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org