Hi Thomas,
(and Steve, since you've been mucking about in the hotplug code,)
Yet another bit of fallout related to hotplug.
This appears to affect 3.0-rt1, 3.0.23-rt29, and 3.2.9-rt17.
(Thus probably all 3.x versions, but I haven't been masochistic
enough to check.)
If not defined CONFIG_PREEMPT_RT_FULL then
- hotplug_lock() is a mutex_lock()
- cpu_hotplug_begin() calls hotplug_lock()
- _cpu_down() calls cpu_hotplug_begin() with preemption
disabled (disabled by the migrate_disable())
The call to cpu_hotplug_begin() is not in a preempt disabled
region until hotplug-use-migrate-disable.patch. This patch
moves the preempt_enable() (aka migrate_enable()) from just
before calling cpu_hotplug_begin() to after "out_cancel:".
The BUG can be triggered by:
echo 0 > /sys/devices/system/cpu/cpu1/online
-Frank
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