linux-kernel - Re: [PATCH 3/6] x86/dumpstack: make printk_stack

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Date:   Wed, 24 Aug 2016 13:43:27 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH 3/6] x86/dumpstack: make printk_stack_address() more
 generally useful

On Wed, Aug 24, 2016 at 10:28:38AM -0700, Joe Perches wrote:
> On Wed, 2016-08-24 at 11:50 -0500, Josh Poimboeuf wrote:
> > Change printk_stack_address() to be useful when called by an unwinder
> > outside the context of dump_trace().
> > 
> > Specifically:
> > 
> > - printk_stack_address()'s 'data' argument is always used as the log
> >   level string.  Make that explicit.
> 
> If this is true, and I'm not sure it is as I believe
> there are static strings emitted like EOE and IRQ,
> shouldn't this bubble up through the calling tree?
>
> > - Call touch_nmi_watchdog().
> []
> > diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> []
> > @@ -26,10 +26,11 @@ int kstack_depth_to_print = 3 * STACKSLOTS_PER_LINE;
> >  static int die_counter;
> >  
> >  static void printk_stack_address(unsigned long address, int reliable,
> > -		void *data)
> > +				 char *log_lvl)
> >  {
> > +	touch_nmi_watchdog();
> >  	printk("%s [<%p>] %s%pB\n",
> > -		(char *)data, (void *)address, reliable ? "" : "? ",
> > +		log_lvl, (void *)address, reliable ? "" : "? ",
> >  		(void *)address);
> >  }
> >  
> > @@ -148,7 +149,6 @@ static int print_trace_stack(void *data, char *name)
> >   */
> >  static int print_trace_address(void *data, unsigned long addr, int reliable)
> >  {
> > -	touch_nmi_watchdog();
> >  	printk_stack_address(addr, reliable, data);
> >  	return 0;
> >  }
> 
> like for data here?

This function needs to keep its 'void *data' argument because it's a
callback for stacktrace_ops, so it has to conform to the callback
interface.  'data' is used for passing a pointer to an opaque data
structure to the callback.

Also this is the only caller of printk_stack_address(), so there's
nowhere else to bubble it up to.

-- 
Josh