linux-kernel - Re: [PATCH 7/7] bug: Move WARN_ON() "cut here" into exception handler

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Message-ID: <06ba33fd-27cc-3816-1cdf-70616b1782dd@c-s.fr>
Date:   Tue, 20 Aug 2019 12:58:49 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Drew Davenport <ddavenport@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Feng Tang <feng.tang@...el.com>,
        Petr Mladek <pmladek@...e.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        YueHaibing <yuehaibing@...wei.com>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] bug: Move WARN_ON() "cut here" into exception handler



Le 20/08/2019 à 12:06, Peter Zijlstra a écrit :
> On Mon, Aug 19, 2019 at 04:41:11PM -0700, Kees Cook wrote:
> 
>> diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
>> index 588dd59a5b72..da471fcc5487 100644
>> --- a/include/asm-generic/bug.h
>> +++ b/include/asm-generic/bug.h
>> @@ -10,6 +10,7 @@
>>   #define BUGFLAG_WARNING		(1 << 0)
>>   #define BUGFLAG_ONCE		(1 << 1)
>>   #define BUGFLAG_DONE		(1 << 2)
>> +#define BUGFLAG_PRINTK		(1 << 3)
>>   #define BUGFLAG_TAINT(taint)	((taint) << 8)
>>   #define BUG_GET_TAINT(bug)	((bug)->flags >> 8)
>>   #endif
> 
>> diff --git a/lib/bug.c b/lib/bug.c
>> index 1077366f496b..6c22e8a6f9de 100644
>> --- a/lib/bug.c
>> +++ b/lib/bug.c
>> @@ -181,6 +181,15 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
>>   		}
>>   	}
>>   
>> +	/*
>> +	 * BUG() and WARN_ON() families don't print a custom debug message
>> +	 * before triggering the exception handler, so we must add the
>> +	 * "cut here" line now. WARN() issues its own "cut here" before the
>> +	 * extra debugging message it writes before triggering the handler.
>> +	 */
>> +	if ((bug->flags & BUGFLAG_PRINTK) == 0)
>> +		printk(KERN_DEFAULT CUT_HERE);
> 
> I'm not loving that BUGFLAG_PRINTK name, BUGFLAG_CUT_HERE makes more
> sense to me.
> 

Actually it would be BUGFLAG_NO_CUT_HERE then, otherwise all arches not 
using the generic macros will have to add the flag to get the "cut here" 
line.

Christophe