On 03/09/12 18:03, Steven Rostedt wrote: > 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? Yes, that is the problem. But it is due to the RT patches, not present in mainline. >> - 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. Yep, I've been watching all the hotplug related conversations with interest... -Frank -- 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
