Messages in this thread |  | | | Date | Thu, 10 Jul 2008 17:32:30 -0700 | | From | "Paul Menage" <> | | Subject | Re: [RFC][PATCH] CGroups: Add a per-subsystem hierarchy lock |
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On Wed, Jul 2, 2008 at 9:46 PM, Max Krasnyansky <maxk@qualcomm.com> wrote: > > mkdir /dev/cpuset > mount -t cgroup -o cpuset cpuset /dev/cpuset > mkdir /dev/cpuset/0 > mkdir /dev/cpuset/1 > echo 0-2 > /dev/cpuset/0/cpuset.cpus > echo 3 > /dev/cpuset/1/cpuset.cpus > echo 0 > /dev/cpuset/cpuset.sched_load_balance > echo 0 > /sys/devices/system/cpu/cpu3/online >
OK, I still can't reproduce this, on a 2-cpu system using one cpu for each cpuset.
But the basic problem seemns to be that we have cpu_hotplug.lock taken at the outer level (when offlining a CPU) and at the inner level (via get_online_cpus() called from the guts of partition_sched_domains(), if we didn't already take it at the outer level.
While looking at the code trying to figure out a nice way around this, it struck me that we have the call path
cpuset_track_online_nodes() -> common_cpu_mem_hotplug_unplug() -> scan_for_empty_cpusets() -> access cpu_online_map with no calls to get_online_cpus()
Is that allowed? Maybe we need separate versions of scan_for_empty_cpusets() that look at memory and cpus?
I think that we're going to want eventually a solution such pushing the locking of cpuset_subsys.hierarchy_mutex down into the first part of partition_sched_domains, that actually walks the cpuset tree
Paul
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