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SubjectRe: [PATCH 1/3] stop_machine: kill __stop_machine()
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On Thu, 2011-06-16 at 10:37 -0700, Suresh Siddha wrote:
> On Thu, 2011-06-16 at 05:12 -0700, Peter Zijlstra wrote:
> > On Tue, 2011-06-14 at 19:06 +0200, Tejun Heo wrote:
> > Please have a look at:
> >
> > ---
> > commit d91309f69b7bdb64aeb30106fde8d18c5dd354b5
> > Author: Peter Zijlstra <peterz@infradead.org>
> > Date: Fri Feb 11 22:07:46 2011 +0100
> >
> > x86: Fix text_poke_smp_batch() deadlock
> >
> > Fix this deadlock - we are already holding the mutex:
> >
> ...
> > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> > index 1236085..7038b95 100644
> > --- a/arch/x86/kernel/alternative.c
> > +++ b/arch/x86/kernel/alternative.c
> > @@ -671,7 +671,7 @@ void __kprobes text_poke_smp_batch(struct text_poke_param *params, int n)
> >
> > atomic_set(&stop_machine_first, 1);
> > wrote_text = 0;
> > - stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
> > + __stop_machine(stop_machine_text_poke, (void *)&tpp, NULL);
> > }
> >
> > #if defined(CONFIG_DYNAMIC_FTRACE) || defined(HAVE_JUMP_LABEL)
> >
>
> Peter, So it looks like we are allowing a new cpu to come online in
> parallel, while we poke the text? Isn't it a problem? What am I missing?

the caller already did get_online_cpus(),

do_optimize_kprobes()
get_online_cpus()
arch_optimize_kprobes()
text_poke_smp_batch()
put_online_cpus()




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