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    SubjectRe: [RFC][PATCH v2 5/5] sched: User Mode Concurency Groups
    On Mon, Jan 24, 2022 at 10:46:17PM +0800, Tao Zhou wrote:

    > > +/* Called from syscall exit path and exceptions that can schedule */
    > > +void umcg_sys_exit(struct pt_regs *regs)
    > > +{
    > > + struct task_struct *tsk = current;
    > > + long syscall = syscall_get_nr(tsk, regs);
    > > +
    > > + if (syscall == __NR_umcg_wait ||
    > > + syscall == __NR_umcg_ctl)
    > > + return;
    > > +
    > > + if (tsk->umcg_server) {
    > > + /*
    > > + * Didn't block, we done.
    > > + */
    > > + umcg_unpin_pages();
    > > + return;
    > > + }
    > > +
    > > + umcg_unblock_and_wait();
    >
    > umcg_unblock_and_wait() -> umcg_enqueue_and_wake() ->
    > umcg_wake_server() -> umcg_wake_task(tsk->umcg_server, ...)
    >
    > tsk->umcg_server is NULL here and umcg_wake_task() use it to update
    > state in umcg_update_state(NULL, ...), that means tsk->umcg_clock
    > will happen something i do not know.

    I think umcg_unblock_and_wait() will repin, at which point we should
    have tsk->umcg_server again.

    > There are two places to call umcg_unblock_and_wait(). One is in
    > umcg_register() where the server is set. Another one is in
    > umcg_sys_exit() where the server is not set. May use a bool to
    > indicate if the server is set.

    I'm not sure what you're on about, but I absolutely hate redundant
    state, that only leads to problems.

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