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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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