Re: [PATCH] ppc64: Fix cpu_up race

From: Joel Schopp (jschopp_at_austin.ibm.com)
Date: 07/30/04

  • Next message: Giuliano Pochini: "Re: [PATCH][PPC32] Makefile cleanups and gcc-3.4+binutils-2.14 c" 
    Date:	Fri, 30 Jul 2004 14:03:31 -0500
To: vatsa@in.ibm.com

    I've tested this patch extensively and it does fix the race.

    In more detail the race is that the cpu can be running before it is
    marked in the cpu_online_map. While running it can go idle and the idle
    loop checks cpu_online_map, sees that it is not set, and assumes that a
    hotplug remove is in progress and that it should stop itself. By the
    time the cpu is marked online it is stopped.

    Srivatsa Vaddagiri wrote:

    > On Thu, Jul 29, 2004 at 03:30:11PM +1000, Anton Blanchard wrote:
    >
    >>
    >>
    >>>I think Anton pushed this to ameslab. I presume there should be some mechanism
    >>>for ameslab stuff to be included mainline. If there is such mechanism, then
    >>>I dont want to push the patch myself.
    >>
    >>It looks good, could you send it directly to akpm, ccing me?
    >
    >
    > Andrew,
    > Patch below fixes a cpu_up race in PPC64. Please apply.
    >
    >
    > Signed-off-by : Srivatsa Vaddagiri <vatsa@in.ibm.com>
    > Signed-off-by : Anton Blanchard <anton@samba.org>
    >
    >
    > ---
    >
    > linux-2.6.8-rc2-vatsa/arch/ppc64/kernel/smp.c | 10 +++++++++-
    > 1 files changed, 9 insertions(+), 1 deletion(-)
    >
    > diff -puN arch/ppc64/kernel/smp.c~ppc64_cpu_up_fix arch/ppc64/kernel/smp.c
    > --- linux-2.6.8-rc2/arch/ppc64/kernel/smp.c~ppc64_cpu_up_fix 2004-07-30 10:33:55.000000000 +0530
    > +++ linux-2.6.8-rc2-vatsa/arch/ppc64/kernel/smp.c 2004-07-30 10:34:02.000000000 +0530
    > @@ -927,7 +927,11 @@ int __devinit __cpu_up(unsigned int cpu)
    >
    > if (smp_ops->give_timebase)
    > smp_ops->give_timebase();
    > - cpu_set(cpu, cpu_online_map);
    > +
    > + /* Wait until cpu puts itself in the online map */
    > + while (!cpu_online(cpu))
    > + cpu_relax();
    > +
    > return 0;
    > }
    >
    > @@ -963,6 +967,10 @@ int __devinit start_secondary(void *unus
    > #endif
    > #endif
    >
    > + spin_lock(&call_lock);
    > + cpu_set(cpu, cpu_online_map);
    > + spin_unlock(&call_lock);
    > +
    > local_irq_enable();
    >
    > return cpu_idle(NULL);
    >
    > _
    >
    -
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