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    SubjectRe: [PATCH v2 0/3] Freezer, CPU hotplug, x86 Microcode: Fix task freezing failures
    On 10/10/2011 08:53 PM, Alan Stern wrote:
    > On Mon, 10 Oct 2011, Srivatsa S. Bhat wrote:
    >> When CPU hotplug is run along with suspend/hibernate tests using
    >> the pm_test framework, even at the freezer level, we hit task freezing
    >> failures. One such failure was reported here:
    >> An excerpt of the log:
    >> Freezing of tasks failed after 20.01 seconds (2 tasks refusing to
    >> freeze, wq_busy=0):
    >> invert_cpu_stat D 0000000000000000 5304 20435 17329 0x00000084
    >> ffff8801f367bab8 0000000000000046 ffff8801f367bfd8 00000000001d3a00
    >> ffff8801f367a010 00000000001d3a00 00000000001d3a00 00000000001d3a00
    >> ffff8801f367bfd8 00000000001d3a00 ffff880414cc6840 ffff8801f36783c0
    >> Call Trace:
    >> [<ffffffff81532de5>] schedule_timeout+0x235/0x320
    >> [<ffffffff81532a0b>] wait_for_common+0x11b/0x170
    >> [<ffffffff81532b3d>] wait_for_completion+0x1d/0x20
    >> [<ffffffff81364486>] _request_firmware+0x156/0x2c0
    >> [<ffffffff81364686>] request_firmware+0x16/0x20
    >> [<ffffffffa01f0da0>] request_microcode_fw+0x70/0xf0 [microcode]
    >> [<ffffffffa01f0390>] microcode_init_cpu+0xc0/0x100 [microcode]
    >> [<ffffffffa01f14b4>] mc_cpu_callback+0x7c/0x11f [microcode]
    >> [<ffffffff815393a4>] notifier_call_chain+0x94/0xd0
    >> [<ffffffff8109770e>] __raw_notifier_call_chain+0xe/0x10
    >> [<ffffffff8106d000>] __cpu_notify+0x20/0x40
    >> [<ffffffff8152cf5b>] _cpu_up+0xc7/0x10e
    >> [<ffffffff8152d07b>] cpu_up+0xd9/0xec
    >> [<ffffffff8151e599>] store_online+0x99/0xd0
    >> [<ffffffff81355eb0>] sysdev_store+0x20/0x30
    >> [<ffffffff811f3096>] sysfs_write_file+0xe6/0x170
    >> [<ffffffff8117ee50>] vfs_write+0xd0/0x1a0
    >> [<ffffffff8117f024>] sys_write+0x54/0xa0
    >> [<ffffffff8153df02>] system_call_fastpath+0x16/0x1b
    >> The reason behind this failure is explained below:
    >> The x86 microcode update driver has callbacks registered for CPU hotplug
    >> events such as a CPU getting offlined or onlined. Things go wrong when a
    >> CPU hotplug stress test is carried out along with a suspend/resume operation
    >> running simultaneously. Upon getting a CPU_DEAD notification (for example,
    >> when a CPU offline occurs with tasks not frozen), the microcode callback
    >> frees up the microcode and invalidates it. Later, when that CPU gets onlined
    >> with tasks being frozen, the microcode callback (for the CPU_ONLINE_FROZEN
    >> event) tries to apply the microcode to the CPU; doesn't find it and hence
    >> depends on the (currently frozen) userspace to get the microcode again. This
    >> leads to the numerous "WARNING"s at drivers/base/firmware_class.c which
    >> eventually leads to task freezing failures in the suspend code path, as has
    >> been reported.
    >> So, this patch series addresses this issue by ensuring that CPU hotplug and
    >> suspend/hibernate don't run in parallel, thereby fixing the task freezing
    >> failures.
    > The seems like entirely the wrong way to go about solving this problem.
    > The kernel shouldn't be responsible for making hotplug stress tests
    > exclusive with system sleep. Whoever is running those tests should be
    > smart enough to realize what's wrong if system sleep interferes with a
    > test.
    > Furthermore, if the entire problem is lack of CPU microcode, hasn't
    > that been fixed already? There recently was a patch to avoid releasing
    > microcode after it was first loaded -- the idea being that there would
    > then be no need to get the microcode from userspace again at awkward
    > times while the system is resuming.

    Well, that was the first version of this patch itself :)
    I forgot to give a link to it in the patch description:

    That was my first idea: to avoid releasing microcode after it was first
    loaded. But Tejun and Borislav felt that a better way to fix the problem
    would be to mutually exclude CPU hotplug and suspend/hibernate.
    And later on, Borislav Acked that one-line patch on the grounds that even
    though that was not the best solution for the bug, it is an optimization
    in its own right.
    And then I posted that one-line patch with a revised motivation:

    Srivatsa S. Bhat <>
    Linux Technology Center,
    IBM India Systems and Technology Lab

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      Last update: 2011-10-10 17:43    [W:0.026 / U:2.936 seconds]
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