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    SubjectRe: [PATCH -tip 22/32] sched: Split the cookie and setup per-task cookie on fork
    On Wed, Nov 25, 2020 at 12:10:14PM +0100, Peter Zijlstra wrote:
    > On Tue, Nov 17, 2020 at 06:19:52PM -0500, Joel Fernandes (Google) wrote:
    > > +void sched_core_tag_requeue(struct task_struct *p, unsigned long cookie, bool group)
    > > +{
    > > + if (!p)
    > > + return;
    > > +
    > > + if (group)
    > > + p->core_group_cookie = cookie;
    > > + else
    > > + p->core_task_cookie = cookie;
    > > +
    > > + /* Use up half of the cookie's bits for task cookie and remaining for group cookie. */
    > > + p->core_cookie = (p->core_task_cookie <<
    > > + (sizeof(unsigned long) * 4)) + p->core_group_cookie;
    >
    > This seems dangerous; afaict there is nothing that prevents cookie
    > collision.

    This is fixed in a later patch by Josh "sched: Refactor core cookie into
    struct" where we are having independent fields for each type of cookie.

    I'll squash it next time I post to prevent confusion. Thanks,

    - Joel

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