Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes: > On Tue, May 19, 2015 at 02:15:41PM +0200, Vitaly Kuznetsov wrote: >> Loaded Hyper-V module will use these functions to disable CPU hotplug >> under certain circumstances. > > What's wrong with get_online_cpus() ? We need to disable cpu offlining permanently (till the module is unloaded but this is highly unlikely). If we do get_online_cpus() instead we get # echo 0 > /sys/devices/system/cpu/cpu1/online <nothing happens, pemanent hang followed by the following:> [ 240.247109] INFO: task bash:972 blocked for more than 120 seconds. [ 240.248937] Not tainted 4.1.0-rc3_bug1167380_test_rkr+ #602 [ 240.250515] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 240.252379] bash D ffff880021b83c18 0 972 939 0x00000004 [ 240.255068] ffff880021b83c18 0000000000000001 0000000000000046 ffff880021b83be8 [ 240.258140] ffffffff81fdcdb0 ffff880037dbcfc0 ffff880037203bd0 ffffffff81fdcdb8 [ 240.261275] ffff880021b84000 0000000000000001 0000000000000000 0000000000000001 [ 240.264402] Call Trace: [ 240.265423] [<ffffffff81aecf77>] schedule+0x37/0x90 [ 240.266748] [<ffffffff81081872>] cpu_hotplug_begin+0xd2/0xe0 [ 240.268210] [<ffffffff810817a5>] ? cpu_hotplug_begin+0x5/0xe0 [ 240.269675] [<ffffffff810cb860>] ? prepare_to_wait_event+0xf0/0xf0 [ 240.271285] [<ffffffff81ad561a>] _cpu_down+0x8a/0x300 [ 240.275294] [<ffffffff81ad58c6>] cpu_down+0x36/0x50 [ 240.276680] [<ffffffff8160f954>] cpu_subsys_offline+0x14/0x20 [ 240.278145] [<ffffffff8160a505>] device_offline+0xa5/0xd0 [ 240.279618] [<ffffffff8160a620>] online_store+0x50/0xa0 [ 240.280991] [<ffffffff81607678>] dev_attr_store+0x18/0x30 ... And if we do the cpu_hotplug_disable() call we get: # echo 0 > /sys/devices/system/cpu/cpu1/online -bash: echo: write error: Device or resource busy This behavior is preferable. -- Vitaly _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
