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SubjectRe: [PATCH] cgroup/cpuset: remove circular dependency deadlock
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On 09/06/2017 07:48 AM, Prateek Sood wrote:
> 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 <prsood@codeaurora.org>

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

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