linux-kernel - Re: [PATCH v2 7/7] bug: Move WARN_ON() "cut here" into exception handler

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Message-ID: <201909100157.CEE99802C@keescook>
Date:   Tue, 10 Sep 2019 01:59:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     20190819234111.9019-8-keescook@...omium.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        Peter Zijlstra <peterz@...radead.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 v2 7/7] bug: Move WARN_ON() "cut here" into exception
 handler

On Tue, Sep 10, 2019 at 01:05:39AM +0900, Sergey Senozhatsky wrote:
> On (08/20/19 09:47), Kees Cook wrote:
> [..]
> > @@ -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_NO_CUT_HERE) == 0)
> > +		printk(KERN_DEFAULT CUT_HERE);
> 
> Shouldn't this be pr_warn() or pr_crit()?

The pr_* helpers here would (potentially) add unwanted prefixes, so
those aren't used. KERN_DEFAULT is used here because that's how it's
always been printed. I didn't want to change that for this refactoring
work. I'm not opposed to it, generally speaking, though. :)

-- 
Kees Cook