Messages in this thread | | | Date | Thu, 19 Jul 2012 19:05:51 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH] x86, mm: Send tlb flush IPIs to online cpus only |
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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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