Re: [PATCH] cgroup/cpuset: remove circular dependency deadlock

On 09/06/2017 06:26 PM, Waiman Long wrote:

On 09/06/2017 07:48 AM, Prateek Sood wrote:

quoted

Remove circular dependency deadlock in a scenario where hotplug of CPU is
being done while there is updation in cgroup and cpuset triggered from
userspace.

Example scenario:
kworker/0:0 => kthreadd => init:729 => init:1 => kworker/0:0

kworker/0:0 - lock(cpuhotplug.mutex)  [held]
              flush(work)   [no high prio workqueue available on CPU]
              wait_for_completion()

kthreadd    - percpu_down_read(cgroup_threadgroup_rwsem)  [waiting]

init:729    - percpu_down_write(cgroup_threadgroup_rwsem)   [held]
              lock(cpuset_mutex)   [waiting]

init:1      - lock(cpuset_mutex)   [held]
              lock(cpuhotplug.mutex)   [waiting]

Eliminate this dependecy by reordering locking of cpuset_mutex
and cpuhotplug.mutex in following order
1. Acquire cpuhotplug.mutex
2. Acquire cpuset_mutex

Signed-off-by: Prateek Sood <redacted>

Is this patch for the latest upstream kernel or 4.4? There is no
cpuhotplug.mutex anymore in upstream kernel. It is a per-cpu rwsem
cpu_hotplug_lock.

Cheers,
Longman

Thanks for inputs, I will check latest kernel for details

Regards
Prateek

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