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    SubjectRe: [PATCH] x86, mm: Send tlb flush IPIs to online cpus only
    On 07/19/2012 07:02 PM, Borislav Petkov wrote:
    > On Thu, Jul 19, 2012 at 06:27:33PM +0530, Srivatsa S. Bhat wrote:
    >
    > [ … ]
    >
    >> So we are sending an IPI to a cpu which is now offline. Once a cpu is offline,
    >> it will no longer respond to IPIs. This explains the softlockup.
    >>
    >> A cpu in the mm_cpumask could go offline before we send the invalidate
    >> IPI causing us to wait forever. Avoid this by sending the IPI to only the
    >> online cpus.
    >>
    >> [Since flush_tlb_others_ipi() is always called with preempt disabled, it is
    >> not possible for a CPU to go offline once we enter this function, because
    >> CPU offline goes through the stop_machine() stuff (which cannot proceed until
    >> all preempt disabled sections are exited). So we don't have to worry about
    >> any race between CPU offline and the target cpumask calculation in
    >> flush_tlb_others_ipi().]
    >>
    >> Addresses http://crosbug.com/31737
    >>
    >> Reported-and-debugged-by: Mandeep Singh Baines <msb@chromium.org>
    >> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    >> Acked-by: Mandeep Singh Baines <msb@chromium.org>
    >> Cc: Thomas Gleixner <tglx@linutronix.de>
    >> Cc: Ingo Molnar <mingo@redhat.com>
    >> Cc: "H. Peter Anvin" <hpa@zytor.com>
    >> Cc: x86@kernel.org
    >> Cc: Tejun Heo <tj@kernel.org>
    >> Cc: Andrew Morton <akpm@linux-foundation.org>
    >> Cc: Stephen Rothwell <sfr@canb.auug.org.au>
    >> Cc: Christoph Lameter <cl@gentwo.org>
    >> Cc: Olof Johansson <olofj@chromium.org>
    >> ---
    >>
    >> arch/x86/mm/tlb.c | 6 +++++-
    >> 1 files changed, 5 insertions(+), 1 deletions(-)
    >>
    >> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
    >> index 5e57e11..9d387a9 100644
    >> --- a/arch/x86/mm/tlb.c
    >> +++ b/arch/x86/mm/tlb.c
    >> @@ -186,7 +186,11 @@ static void flush_tlb_others_ipi(const struct cpumask *cpumask,
    >>
    >> f->flush_mm = mm;
    >> f->flush_va = va;
    >> - if (cpumask_andnot(to_cpumask(f->flush_cpumask), cpumask, cpumask_of(smp_processor_id()))) {
    >> +
    >> + cpumask_and(to_cpumask(f->flush_cpumask), cpumask, cpu_online_mask);
    >> + cpumask_clear_cpu(smp_processor_id(), to_cpumask(f->flush_cpumask));
    >> +
    >> + if (!cpumask_empty(to_cpumask(f->flush_cpumask))) {
    >
    > FWIW, there's code in tip/x86/mm which reworks all that and
    > flush_tlb_others_ipi along with the 32 TLB flush vectors are being
    > removed in favor of a smp_call_function_many thing. And it should be
    > hotplug-safe since it must be called with preemption disabled anyway.
    >

    Oh.. ok.. Then this patch is perhaps unnecessary..
    Thanks for the info!

    Regards,
    Srivatsa S. Bhat

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