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If the scheduler cannot find an allowed CPU for a task, cpuset_cpus_allowed_fallback() will widen the affinity to cpu_possible_mask if cgroup v1 is in use. In preparation for allowing architectures to provide their own fallback mask, just return early if we're not using cgroup v2 and allow select_fallback_rq() to figure out the mask by itself. Cc: Li Zefan <lizefan@huawei.com> Cc: Tejun Heo <tj@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Quentin Perret <qperret@google.com> Signed-off-by: Will Deacon <will@kernel.org> [will: Check task_cpu_possible_mask() in v2 mode as per on-list comments] Link: https://lore.kernel.org/r/20201217121552.ds7g2icvqp5nvtha@e107158-lin.cambridge.arm.com Bug: 178507149 Link: https://lore.kernel.org/linux-arch/20201208132835.6151-8-will@kernel.org/ Signed-off-by: Will Deacon <willdeacon@google.com> Change-Id: I7a6b234c28495bae6feeecceafb841aae4de6046