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: >> https://lkml.org/lkml/2011/9/5/28 >> >> 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: http://thread.gmane.org/gmane.linux.kernel/1198291/focus=1200591 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: http://thread.gmane.org/gmane.linux.kernel/1200882 -- Regards, Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> Linux Technology Center, IBM India Systems and Technology Lab -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
