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    SubjectCPU hotplug: system hang on CPU hot remove during `pfmon --system-wide'

    I found a bug on CPU hotplug. If `pfmon --system-wide' is running,
    CPU hot remove causes system hang. On the other hand, CPU hot add
    during that command seems to work fine.

    I detected this problem on my ia64 box, and I don't know that this
    problem is also occur on any arch or freezer based CPU hotplug.
    Since I'm investigating this problem now, I'm glad if someone
    reports the test result on other arch or freezer.

    Currently I don't know anything about the cause of this problem.

    How To Reproduce

    Assuming you have two terminal, named term A and term B.

    1) execute pfmon from term A

    $ pfmon --system-wide
    <press ENTER to stop session>

    2) issue CPU hot remove from term B

    # echo 0 >/sys/devices/system/cpu/cpu1/online

    3) Press enter from term B

    Expected Result

    Succeed to offline CPU

    Actual Result

    System hang occurs and there are the following messages on serial console.

    CPU0 1925600 CPU_CYCLES
    CPU1 could not stop monitoring, CPU may be offline, check results
    pfm_write_old_pmds error [3] Device or resource busy
    pfmon_read_pmds error Device or resource busy
    CPU1 read_results error


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      Last update: 2007-05-28 03:59    [W:0.025 / U:43.000 seconds]
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