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    SubjectRe: CPU softlockup due to smp_call_function()
    On Thu, Apr 5, 2012 at 2:24 PM, Avi Kivity <avi@redhat.com> wrote:
    > On 04/04/2012 11:12 PM, Sasha Levin wrote:
    >> Hi all,
    >>
    >> I've starting seeing soft lockups resulting from smp_call_function()
    >> calls. I've attached two different backtraces of this happening with
    >> different code paths.
    >>
    >> This is running inside a KVM guest with the trinity fuzzer, using
    >> today's linux-next kernel.
    >>
    >> [ 6540.134009] BUG: soft lockup - CPU#0 stuck for 22s! [kworker/u:1:38]
    >> [ 6540.134048] irq event stamp: 286811770
    >> [ 6540.134048] hardirqs last  enabled at (286811769):
    >> [<ffffffff82669e74>] restore_args+0x0/0x30
    >> [ 6540.134048] hardirqs last disabled at (286811770):
    >> [<ffffffff8266b3ea>] apic_timer_interrupt+0x6a/0x80
    >> [ 6540.134048] softirqs last  enabled at (286811768):
    >> [<ffffffff810b746e>] __do_softirq+0x16e/0x190
    >> [ 6540.134048] softirqs last disabled at (286811749):
    >> [<ffffffff8266bdec>] call_softirq+0x1c/0x30
    >> [ 6540.134048] CPU 0
    >> [ 6540.134048] Pid: 38, comm: kworker/u:1 Tainted: G        W
    >> 3.4.0-rc1-next-20120404-sasha-dirty #72
    >> [ 6540.134048] RIP: 0010:[<ffffffff8111f30e>]  [<ffffffff8111f30e>]
    >> smp_call_function_many+0x27e/0x2a0
    >>
    >
    > This cpu is waiting for some other cpu to process a function (likely
    > rps_trigger_softirq(), from the trace).  Can you get a backtrace on all
    > cpus when this happens?
    >
    > It would be good to enhance smp_call_function_*() to do this
    > automatically when it happens - it's spinning there anyway, so it might
    > as well count the iterations and NMI the lagging cpu if it waits for too
    > long.

    What do you think about modifying the softlockup detector to NMI all
    CPUs if it's going to panic because it detected a lockup?
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