On Fri, 2012-03-09 at 17:51 -0800, Frank Rowand wrote: > 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 So you're saying that there's a bug with PREEMPT_RT off? > > - 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 Note, there's a lot more wrong with hotplug in rt than this. The hotplug code really needs a total rewrite for RT to work with it. It probably should have a total rewrite in mainline anyway. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
