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    SubjectRe: [PATCH 4.19 16/17] kthread: Extract KTHREAD_IS_PER_CPU
    Hi!

    > From: Peter Zijlstra <peterz@infradead.org>
    >
    > [ Upstream commit ac687e6e8c26181a33270efd1a2e2241377924b0 ]
    >
    > There is a need to distinguish geniune per-cpu kthreads from kthreads
    > that happen to have a single CPU affinity.
    >
    > Geniune per-cpu kthreads are kthreads that are CPU affine for
    > correctness, these will obviously have PF_KTHREAD set, but must also
    > have PF_NO_SETAFFINITY set, lest userspace modify their affinity and
    > ruins things.
    >
    > However, these two things are not sufficient, PF_NO_SETAFFINITY is
    > also set on other tasks that have their affinities controlled through
    > other means, like for instance workqueues.
    >
    > Therefore another bit is needed; it turns out kthread_create_per_cpu()
    > already has such a bit: KTHREAD_IS_PER_CPU, which is used to make
    > kthread_park()/kthread_unpark() work correctly.
    >
    > Expose this flag and remove the implicit setting of it from
    > kthread_create_on_cpu(); the io_uring usage of it seems dubious at
    > best.

    AFAIK this should not be in 4.19/5.10 as it does not fix anything w/o
    5ba2ffba13a1e. Nobody calls kthread_is_per_cpu() in those kernels.

    Best regards,
    Pavel

    --
    http://www.livejournal.com/~pavelmachek
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