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    SubjectRe: smp_call_function_single lockups
    On Mon, Feb 23, 2015 at 11:32:50AM -0800, Linus Torvalds wrote:
    > On Mon, Feb 23, 2015 at 6:01 AM, Rafael David Tinoco <inaddy@ubuntu.com> wrote:
    > >
    > > This is v3.19 + your patch (smp acquire/release)
    > > - (nested kvm with 2 vcpus on top of proliant with x2apic cluster mode
    > > and acpi_idle)
    >
    > Hmm. There is absolutely nothing else going on on that machine, except
    > for the single call to smp_call_function_single() that is waiting for
    > the CSD to be released.
    >
    > > * It looks like we got locked because of reentrant flush_tlb_* through
    > > smp_call_*
    > > but I'll leave it to you.
    >
    > No, that is all a perfectly regular callchain:
    >
    > .. native_flush_tlb_others -> smp_call_function_many ->
    > smp_call_function_single
    >
    > but the stack contains some stale addresses (one is probably just from
    > smp_call_function_single() calling into "generic_exec_single()", and
    > thus the stack contains the return address inside
    > smp_call_function_single() in _addition_ to the actual place where the
    > watchdog timer then interrupted it).
    >
    > It all really looks very regular and sane, and looks like
    > smp_call_function_single() is happily just waiting for the IPI to
    > finish in the (inlined) csd_lock_wait().
    >
    > I see nothing wrong at all.

    [11396.096002] Hardware name: OpenStack Foundation OpenStack Nova, BIOS Bochs 01/01/2011

    But its a virtual machine right? Its not running bare metal, its running
    a !virt kernel on a virt machine, so maybe some of the virt muck is
    borked?

    A very subtly broken APIC emulation would be heaps of 'fun'.


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