From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 7A28C6B007E for ; Mon, 2 May 2016 11:35:04 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id w143so80227539wmw.3 for ; Mon, 02 May 2016 08:35:04 -0700 (PDT) Received: from mail-lf0-x22e.google.com (mail-lf0-x22e.google.com. [2a00:1450:4010:c07::22e]) by mx.google.com with ESMTPS id dw7si5080011lbc.96.2016.05.02.08.35.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 May 2016 08:35:03 -0700 (PDT) Received: by mail-lf0-x22e.google.com with SMTP id y84so191940047lfc.0 for ; Mon, 02 May 2016 08:35:03 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <57276E95.1030201@emindsoft.com.cn> 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> Date: Mon, 2 May 2016 17:35:02 +0200 Message-ID: Subject: Re: [PATCH] mm/kasan/kasan.h: Fix boolean checking issue for kasan_report_enabled() From: Alexander Potapenko Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Chen Gang Cc: Dmitry Vyukov , Andrew Morton , Andrey Ryabinin , kasan-dev , LKML , "linux-mm@kvack.org" , Chen Gang On Mon, May 2, 2016 at 5:13 PM, Chen Gang wrote= : > On 5/2/16 22:23, Alexander Potapenko wrote: >> On Mon, May 2, 2016 at 3:51 PM, Chen Gang wr= ote: >>> >>> OK, thanks. >>> >>> And for "kasan_depth =3D=3D 1", I guess, its meaning is related with >>> kasan_depth[++|--] in kasan_[en|dis]able_current(): >> Assuming you are talking about the assignment of 1 to kasan_depth in >> /include/linux/init_task.h, >> it's somewhat counterintuitive. I think we just need to replace it >> with kasan_disable_current(), and add a corresponding >> kasan_enable_current() to the end of kasan_init. >> > > 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 =3D=3D 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. >>> >>> I guess, we are agree with each other: "We can both issue a WARNING and >>> prevent the actual overflow/underflow.". >> No, I am not sure think that we need to prevent the overflow. >> As I showed before, this may result in kasan_depth being off even in >> the case kasan_enable_current()/kasan_disable_current() are used >> consistently. > > 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=3D0 (which is the default case for every task except for the init, which also gets kasan_depth=3D0 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. > - If we don't prevent the overflow, 2nd enable will cause disable > effect, which will destroy the caller's original work. The subsequent call to kasan_enable_current() will > - Enable/disable mismatch is caused by caller, we can issue warnings, > and skip it (since it is not caused by us). But we can not generate > new issues to the system only because of the caller's issue. > > > Thanks. > -- > Chen Gang (=E9=99=88=E5=88=9A) > > Managing Natural Environments is the Duty of Human Beings. --=20 Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Stra=C3=9Fe, 33 80636 M=C3=BCnchen Gesch=C3=A4ftsf=C3=BChrer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg -- 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