Messages in this thread | | | Date | Mon, 03 Oct 2011 00:43:42 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [BUG] CPU hotplug, freezer: Freezing of tasks failed after 20.00 seconds |
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On 09/06/2011 11:31 AM, Rafael J. Wysocki wrote: > On Tuesday, September 06, 2011, Tejun Heo wrote: >> Hello, again. >> >> On Mon, Sep 05, 2011 at 11:15:12PM +0900, Tejun Heo wrote: >>>> 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 >>> >>> So, this task is trying to bring a CPU up, which triggers firmware >>> helper to load microcode. Firmware class currently sleeps >>> non-interruptibly to wait for firmware load to complete, which is >>> performed by another userland task. Now, the PM freezer doesn't >>> assume that there will be non-freezable wait dependencies among >>> userland tasks. It only knows two levels - userland and kernel tasks >>> - and assumes that the former group may have non-freezable wait >>> dependency on the latter but there's no such dependency among each >>> group itself. If there's such dependency, PM freezer may fail, which >>> is what happened here. >>> >>> ie. the firmware loader userland process got frozen first. >>> invert_cpu_stat trying to bring up CPU was waiting for the firmware >>> loader to finish in non-interruptible sleep, so the freezer couldn't >>> proceed. >> >> Hmmm... I went through the code again and usermodehelper_disable() >> seems to be there to prevent deadlocks like this. usermode helpers >> are drained & plugged before freezing is tried. Rafael, the above >> shouldn't be happening, right? > > No, it shouldn't in theory, but I'm not sure any more after the recent > modifications of firmware loading related to the initialization. I'll have > a closer look tomorrow. >
Hi, I have posted a fix for this bug at https://lkml.org/lkml/2011/10/2/142 With my fix, the numerous "WARNING"s at drivers/base/firmware_class.c disappear and the task freezing failures are fixed too. I have tested this for about 10-12 hours (much more time than what was necessary to reproduce the bug earlier).
-- Regards, Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Linux Technology Center, IBM India Systems and Technology Lab
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