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

Peter Zijlstra
2022-01-24T14:31:20Z

On Fri, Jan 21, 2022 at 04:18:46PM +0100, Peter Zijlstra wrote:
> Something like this, still yuck though. Also still need to write me a
> test for this.
>
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1300,12 +1300,14 @@ struct task_struct {
> clockid_t umcg_clock;
> struct umcg_task __user *umcg_task;
>
> - /* setup by umcg_pin_enter() */
> + /* setup by umcg_pin_pages() */
> struct page *umcg_page;
>
> struct task_struct *umcg_server;
> struct umcg_task __user *umcg_server_task;
> struct page *umcg_server_page;
> +
> + u64 umcg_timeout;
> #endif
>
> struct tlbflush_unmap_batch tlb_ubc;
> --- a/kernel/sched/umcg.c
> +++ b/kernel/sched/umcg.c
> @@ -232,6 +232,8 @@ static int umcg_update_state(struct task
> /* Called from syscall enter path and exceptions that can schedule */
> void umcg_sys_enter(struct pt_regs *regs, long syscall)
> {
> + current->umcg_timeout = 0;
> +
> /* avoid recursion vs our own syscalls */
> if (syscall == __NR_umcg_wait ||
> syscall == __NR_umcg_ctl)
> @@ -519,6 +521,7 @@ void umcg_notify_resume(struct pt_regs *
> struct umcg_task __user *self = tsk->umcg_task;
> bool worker = tsk->flags & PF_UMCG_WORKER;
> u32 state;
> + int ret;
>
> /* avoid recursion vs schedule() */
> if (worker)
> @@ -554,12 +557,17 @@ void umcg_notify_resume(struct pt_regs *
> umcg_unpin_pages();
> }
>
> - switch (umcg_wait(0)) {
> + ret = umcg_wait(tsk->umcg_timeout);

Oh how I hate signals... this can get scribbled by a syscall/fault from
sigcontext :/

Maybe I can recover the timo argument from the original syscall
pt_regs.. let me try.

> + switch (ret) {
> case 0:
> case -EINTR:
> /* we will resume the wait after the signal */
> break;
>
> + case -ETIMEDOUT:
> + regs_set_return_value(regs, ret);
> + break;
> +
> default:
> UMCG_DIE("wait");
> }
> @@ -759,6 +767,7 @@ SYSCALL_DEFINE2(umcg_wait, u32, flags, u
> switch (ret) {
> case 0: /* all done */
> case -EINTR: /* umcg_notify_resume() will continue the wait */
> + tsk->umcg_timeout = timo;
> ret = 0;
> break;
>