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a22b3d54de
There is a possible race between removing a cgroup diectory that is a partition root and the creation of a new partition. The partition to be removed can be dying but still online, it doesn't not currently participate in checking for exclusive CPUs conflict, but the exclusive CPUs are still there in subpartitions_cpus and isolated_cpus. These two cpumasks are global states that affect the operation of cpuset partitions. The exclusive CPUs in dying cpusets will only be removed when cpuset_css_offline() function is called after an RCU delay. As a result, it is possible that a new partition can be created with exclusive CPUs that overlap with those of a dying one. When that dying partition is finally offlined, it removes those overlapping exclusive CPUs from subpartitions_cpus and maybe isolated_cpus resulting in an incorrect CPU configuration. This bug was found when a warning was triggered in remote_partition_disable() during testing because the subpartitions_cpus mask was empty. One possible way to fix this is to iterate the dying cpusets as well and avoid using the exclusive CPUs in those dying cpusets. However, this can still cause random partition creation failures or other anomalies due to racing. A better way to fix this race is to reset the partition state at the moment when a cpuset is being killed. Introduce a new css_killed() CSS function pointer and call it, if defined, before setting CSS_DYING flag in kill_css(). Also update the css_is_dying() helper to use the CSS_DYING flag introduced by commit |
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