Re: [PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs

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From	Zefan Li <lizefan@huawei.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs
Date	Mon, 04 Jan 2016 03:00:02 +0100
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On 2016/1/1 20:09, Chen Yu wrote:
> Commit be4c9dd7aee5 ("cpuset: enable onlined cpu/node in effective masks")
> leverages cpuset's cpus_allowed and its parent's effective_cpus to calculate
> the new_cpus by:
>
> cpumask_and(&new_cpus, cs->cpus_allowed, parent_cs(cs)->effective_cpus);
>
> However cpus_allowed will also be updated after the CPU is offline, in
> hotplug_update_tasks_legacy, so when the CPU is online again, it will use
> the old cpus_allowed mask to calculate the new_cpus, thus new_cpus will get
> incorrect value after each round of offline/online.
>
> This problem is found on ubuntu 15.10 with cpuset mounted:
>
> 1. echo 0 > /sys/devices/system/cpu/cpu2/online
> 2. echo 1 > /sys/devices/system/cpu/cpu2/online
> 3. cat /sys/fs/cgroup/cpuset/cpuset.cpus
>     0-3
> 4. cat /sys/fs/cgroup/cpuset/user.slice/cpuset.cpus
>     0-1,3
> 5. taskset -c 2 ls
>     taskset: failed to set pid 0's affinity: Invalid argument
>

This is the expected behavior...In legacy hierachy onlining an offlined cpu
won't restore cpuset configurations automatically.

Commit be4c9dd7aee5 changed this behavior, but only for unified hierachy.

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Thread

[PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs Chen Yu <yu.c.chen@intel.com> - 2016-01-01 13:10 +0100
  RE: [PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs "Chen, Yu C" <yu.c.chen@intel.com> - 2016-01-01 13:10 +0100
  Re: [PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs Tejun Heo <tj@kernel.org> - 2016-01-03 15:00 +0100
  Re: [PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs Zefan Li <lizefan@huawei.com> - 2016-01-04 03:00 +0100
    RE: [PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs "Chen, Yu C" <yu.c.chen@intel.com> - 2016-01-04 03:20 +0100
      Re: [PATCH] cpuset: fix cpus_allowed mask for offline/online CPUs Zefan Li <lizefan@huawei.com> - 2016-01-04 03:30 +0100

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