From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f69.google.com (mail-lf0-f69.google.com [209.85.215.69]) by kanga.kvack.org (Postfix) with ESMTP id 698516B007E for ; Mon, 2 May 2016 08:42:09 -0400 (EDT) Received: by mail-lf0-f69.google.com with SMTP id m64so36847757lfd.1 for ; Mon, 02 May 2016 05:42:09 -0700 (PDT) Received: from mail-lf0-x22d.google.com (mail-lf0-x22d.google.com. [2a00:1450:4010:c07::22d]) by mx.google.com with ESMTPS id dw7si4719509lbc.96.2016.05.02.05.42.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 02 May 2016 05:42:07 -0700 (PDT) Received: by mail-lf0-x22d.google.com with SMTP id j8so53985411lfd.2 for ; Mon, 02 May 2016 05:42:07 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <572747C2.5040009@emindsoft.com.cn> References: <1462167374-6321-1-git-send-email-chengang@emindsoft.com.cn> <572735EB.8030300@emindsoft.com.cn> <572747C2.5040009@emindsoft.com.cn> Date: Mon, 2 May 2016 14:42:07 +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 2:27 PM, Chen Gang wrote= : > On 5/2/16 19:21, Dmitry Vyukov wrote: >> On Mon, May 2, 2016 at 1:11 PM, Chen Gang wr= ote: >>> On 5/2/16 16:26, Dmitry Vyukov wrote: >>>> If you want to improve kasan_depth handling, then please fix the >>>> comments and make disable increment and enable decrement (potentially >>>> with WARNING on overflow/underflow). It's better to produce a WARNING >>>> rather than silently ignore the error. We've ate enough unmatched >>>> annotations in user space (e.g. enable is skipped on an error path). >>>> These unmatched annotations are hard to notice (they suppress >>>> reports). So in user space we bark loudly on overflows/underflows and >>>> also check that a thread does not exit with enabled suppressions. >>>> >>> >>> For me, when WARNING on something, it will dummy the related feature >>> which should be used (may let user's hope fail), but should not get the >>> negative result (hurt user's original work). So in our case: >>> >>> - When caller calls kasan_report_enabled(), kasan_depth-- to 0, >>> >>> - When a caller calls kasan_report_enabled() again, the caller will ge= t >>> a warning, and notice about this calling is failed, but it is still >>> in enable state, should not change to disable state automatically. >>> >>> - If we report an warning, but still kasan_depth--, it will let things >>> much complex. >>> >>> And for me, another improvements can be done: >>> >>> - signed int kasan_depth may be a little better. When kasan_depth > 0, >>> it is in disable state, else in enable state. It will be much harder >>> to generate overflow than unsigned int kasan_depth. >>> >>> - Let kasan_[en|dis]able_current() return Boolean value to notify the >>> caller whether the calling succeeds or fails. >> >> Signed counter looks good to me. > > Oh, sorry, it seems a little mess (originally, I need let the 2 patches > in one patch set). > > If what Alexander's idea is OK (if I did not misunderstand), I guess, > unsigned counter is still necessary. I don't think it's critical for us to use an unsigned counter. If we increment the counter in kasan_disable_current() and decrement it in kasan_enable_current(), as Dmitry suggested, we'll be naturally using only positive integers for the counter. If the counter drops below zero, or exceeds a certain number (say, 20), we can immediately issue a warning. >> We can both issue a WARNING and prevent the actual overflow/underflow. >> But I don't think that there is any sane way to handle the bug (other >> than just fixing the unmatched disable/enable). If we ignore an >> excessive disable, then we can end up with ignores enabled >> permanently. If we ignore an excessive enable, then we can end up with >> ignores enabled when they should not be enabled. The main point here >> is to bark loudly, so that the unmatched annotations are noticed and >> fixed. >> > > How about BUG_ON()? As noted by Dmitry in an offline discussion, we shouldn't bail out as long as it's possible to proceed, otherwise the kernel may become very hard to debug. A mismatching annotation isn't a case in which we can't proceed with the execution. > > 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