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由 Bharata B Rao 提交于
Impact: fix cgroups race under rcu-preempt cpuacct_charge() obtains task's ca and does a hierarchy walk upwards. This can race with the task's movement between cgroups. This race can cause an access to freed ca pointer in cpuacct_charge() or access to invalid cgroups pointer of the task. This will not happen with rcu or tree rcu as cpuacct_charge() is called with preemption disabled. However if rcupreempt is used, the race is seen. Thanks to Li Zefan for explaining this. Fix this race by explicitly protecting ca and the hierarchy walk with rcu_read_lock(). Changes for v2: - Update patch descrition (as per Li Zefan's review comments). - Remove comments in cpuacct_charge() which explained why rcu_read_lock() was needed (as per Peter Zijlstra's review comments). Signed-off-by: NBharata B Rao <bharata@linux.vnet.ibm.com> Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Paul Menage <menage@google.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: NBalbir Singh <balbir@linux.vnet.ibm.com> Tested-by: NBalbir Singh <balbir@linux.vnet.ibm.com> Signed-off-by: NIngo Molnar <mingo@elte.hu>
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