linux-kernel - Re: [PATCH v4 01/15] stacktrace/x86: add function for detecting reliable stack traces

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Message-ID: <20170127171346.o7wuvycriajdpixc@treble>
Date:   Fri, 27 Jan 2017 11:13:46 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Jessica Yu <jeyu@...hat.com>, Jiri Kosina <jikos@...nel.org>,
        Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org,
        live-patching@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <heiko.carstens@...ibm.com>, x86@...nel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        Vojtech Pavlik <vojtech@...e.com>, Jiri Slaby <jslaby@...e.cz>,
        Chris J Arges <chris.j.arges@...onical.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>
Subject: Re: [PATCH v4 01/15] stacktrace/x86: add function for detecting
 reliable stack traces

On Fri, Jan 27, 2017 at 09:47:08AM +0100, Miroslav Benes wrote:
> 
> > diff --git a/include/linux/stacktrace.h b/include/linux/stacktrace.h
> > index 0a34489..8e8b67b 100644
> > --- a/include/linux/stacktrace.h
> > +++ b/include/linux/stacktrace.h
> > @@ -18,6 +18,8 @@ extern void save_stack_trace_regs(struct pt_regs *regs,
> >  				  struct stack_trace *trace);
> >  extern void save_stack_trace_tsk(struct task_struct *tsk,
> >  				struct stack_trace *trace);
> > +extern int save_stack_trace_tsk_reliable(struct task_struct *tsk,
> > +					 struct stack_trace *trace);
> >  
> >  extern void print_stack_trace(struct stack_trace *trace, int spaces);
> >  extern int snprint_stack_trace(char *buf, size_t size,
> > @@ -29,12 +31,12 @@ extern void save_stack_trace_user(struct stack_trace *trace);
> >  # define save_stack_trace_user(trace)              do { } while (0)
> >  #endif
> >  
> > -#else
> > +#else /* !CONFIG_STACKTRACE */
> >  # define save_stack_trace(trace)			do { } while (0)
> >  # define save_stack_trace_tsk(tsk, trace)		do { } while (0)
> >  # define save_stack_trace_user(trace)			do { } while (0)
> >  # define print_stack_trace(trace, spaces)		do { } while (0)
> >  # define snprint_stack_trace(buf, size, trace, spaces)	do { } while (0)
> 
> Is there a reason you did not define empty save_stack_trace_tsk_reliable() 
> here? Right, it should not be needed now as livepatching is the only user, 
> but still.

Agreed, thanks.  I'll make the stub return an error, since an empty
stack trace isn't very reliable.

-- 
Josh