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SubjectRe: [PATCH v6 2/8] x86: allow to call text_poke_bp during boot
On Tue, 10 Dec 2013 16:46:12 +0100
Borislav Petkov <bp@alien8.de> wrote:

> On Tue, Dec 10, 2013 at 04:42:14PM +0100, Petr Mladek wrote:
> > We would like to use text_poke_bp in ftrace. It might be called also during
> > boot when there is only one CPU and we do not need to sync the others.
> >
> > The check is must to have because there are also disabled interrupts during
> > the boot. Then the call would cause a deadlock, see the warning in
> > "smp_call_function_many", kernel/smp.c:371.
> >
> > The change is inspired by the code in arch/x86/kernel/ftrace.c.
> >
> > Signed-off-by: Petr Mladek <pmladek@suse.cz>
> > Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> > ---
> > arch/x86/kernel/alternative.c | 17 ++++++++++++++---
> > 1 file changed, 14 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> > index eabed9326d2a..6436beec7b0c 100644
> > --- a/arch/x86/kernel/alternative.c
> > +++ b/arch/x86/kernel/alternative.c
> > @@ -599,6 +599,17 @@ static void do_sync_core(void *info)
> > sync_core();
> > }
> >
> > +static void run_sync(void)
>
> Can we call this sync_cores()?
>
> It is what it does. :)

That can be changed in a later patch if needed. It's a static function
so the visibility is limited. Not to mention, it was just moved from
ftrace.c which calls it run_sync(). We need to keep the same name for
the move to not confuse the history of where it came from.

-- Steve

>
> > +{
> > + /*
> > + * We do not need to sync other cores during boot when there is only one
> > + * CPU enabled. In fact, we must not because there are also disabled
> > + * interrupts. The call would fail because of a potential deadlock.
> > + */
> > + if (num_online_cpus() != 1)
> > + on_each_cpu(do_sync_core, NULL, 1);
> > +}
>



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