linux-kernel - Re: [PATCH 3/4] x86/unwind: include _

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Date:   Tue, 10 Jan 2017 21:02:01 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
cc:     x86@...nel.org, Dave Jones <davej@...emonkey.org.uk>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andy Lutomirski <luto@...capital.net>,
        Brian Gerst <brgerst@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] x86/unwind: include __schedule() in stack traces

On Tue, 10 Jan 2017, Josh Poimboeuf wrote:

> On Tue, Jan 10, 2017 at 11:14:51AM +0100, Miroslav Benes wrote:
> > On Mon, 9 Jan 2017, Josh Poimboeuf wrote:
> > > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > > ---
> > >  arch/x86/include/asm/stacktrace.h |  5 +----
> > >  arch/x86/include/asm/switch_to.h  | 10 +++++++++-
> > >  2 files changed, 10 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
> > > index 20ce3db..2e41c50 100644
> > > --- a/arch/x86/include/asm/stacktrace.h
> > > +++ b/arch/x86/include/asm/stacktrace.h
> > > @@ -52,16 +52,13 @@ static inline bool on_stack(struct stack_info *info, void *addr, size_t len)
> > >  static inline unsigned long *
> > >  get_frame_pointer(struct task_struct *task, struct pt_regs *regs)
> > >  {
> > > -	struct inactive_task_frame *frame;
> > > -
> > >  	if (regs)
> > >  		return (unsigned long *)regs->bp;
> > >  
> > >  	if (task == current)
> > >  		return __builtin_frame_address(0);
> > >  
> > > -	frame = (struct inactive_task_frame *)task->thread.sp;
> > > -	return (unsigned long *)READ_ONCE_NOCHECK(frame->bp);
> > > +	return &((struct inactive_task_frame *)task->thread.sp)->bp;
> > 
> > You effectively remove one of the changes from the previous patch - 
> > READ_ONCE_NOCHECK. Is it intentional?
> 
> Yes, notice that it's no longer reading the value of bp on the stack.
> It's instead getting a pointer to it.  Since there's no longer a stack
> access, READ_ONCE_NOCHECK is no longer needed.

Oh, of course. Sorry for the noise.

Miroslav