Re: [PATCH 3/4] x86/unwind: include __schedule() in stack traces

From	Josh Poimboeuf <jpoimboe@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/4] x86/unwind: include __schedule() in stack traces
Date	2017-01-10 18:30 +0100
Message-ID	<sY8pc-4aE-1@gated-at.bofh.it> (permalink)
References	<sXMyl-7wx-11@gated-at.bofh.it> <sXMyl-7wx-13@gated-at.bofh.it> <sY1H4-8v8-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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@redhat.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.

-- 
Josh

Thread

[PATCH 3/4] x86/unwind: include __schedule() in stack traces Josh Poimboeuf <jpoimboe@redhat.com> - 2017-01-09 19:10 +0100
  Re: [PATCH 3/4] x86/unwind: include __schedule() in stack traces Miroslav Benes <mbenes@suse.cz> - 2017-01-10 11:20 +0100
    Re: [PATCH 3/4] x86/unwind: include __schedule() in stack traces Josh Poimboeuf <jpoimboe@redhat.com> - 2017-01-10 18:30 +0100
      Re: [PATCH 3/4] x86/unwind: include __schedule() in stack traces Miroslav Benes <mbenes@suse.cz> - 2017-01-10 21:10 +0100
  [tip:x86/urgent] x86/unwind: Include __schedule() in stack traces tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2017-01-12 11:20 +0100

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