Re: [RFC][PATCH v2 5/5] sched: User Mode Concurency Groups

On Mon, Jan 24, 2022 at 10:46:17PM +0800, Tao Zhou wrote:

quoted

+/* 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.