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 <[email protected]> > Signed-off-by: Srivatsa S. Bhat <[email protected]> > Acked-by: Mandeep Singh Baines <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: "H. Peter Anvin" <[email protected]> > Cc: [email protected] > Cc: Tejun Heo <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Stephen Rothwell <[email protected]> > Cc: Christoph Lameter <[email protected]> > Cc: Olof Johansson <[email protected]> > --- > > 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. -- Regards/Gruss, Boris. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
