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    SubjectRe: [RFC PATCH] ARM: smp: Fix the CPU hotplug race with scheduler.
    On Mon, Jun 20, 2011 at 05:57:01PM +0530, Santosh Shilimkar wrote:
    > On 6/20/2011 5:49 PM, Russell King - ARM Linux wrote:
    >> On Mon, Jun 20, 2011 at 05:21:48PM +0530, Santosh Shilimkar wrote:
    >>> On 6/20/2011 5:10 PM, Russell King - ARM Linux wrote:
    >
    > [...]
    >
    >>>
    >>> Any pointers on the other question about "why we need to enable
    >>> interrupts before the CPU is ready?"
    >>
    >> To ensure that things like the delay loop calibration and twd calibration
    >> can run, though that looks like it'll run happily enough with the boot
    >> CPU updating jiffies.
    >>
    > I guessed it and had same point as above. Calibration will still
    > work.
    >
    >> However, I'm still not taking your patch because I believe its just
    >> papering over the real issue, which is not as you describe.
    >>
    >> You first need to work out why the spinlock lockup detection is firing
    >> after just 61us rather than the full 1s and fix that.
    >>
    > This is possibly because of my script which doesn't wait for 1
    > second.

    How could a userspace script affect the internal behaviour of
    spin_lock() and the spinlock lockup detector?

    > Latest mainline kernel with omap2plus_defconfig and below simple script
    > to trigger the failure.
    >
    > -------------
    > while true
    > do
    > echo 0 > /sys/devices/system/cpu/cpu1/online
    > echo 1 > /sys/devices/system/cpu/cpu1/online
    > done

    Thanks, I'll give it a go here and see if I can debug it further.


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