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

Josh Poimboeuf
2017-01-10T17:28:53Z

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