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

Tao Zhou
2022-01-27T18:31:36Z

On Thu, Jan 20, 2022 at 04:55:22PM +0100, Peter Zijlstra wrote:

Another iterator of the patch, some nits below.

[...]

> +/*
> + * Pinning a page inhibits rmap based unmap for Anon pages. Doing a load
> + * through the user mapping ensures the user mapping exists.
> + */
> +#define umcg_pin_and_load(_self, _pagep, _member) \
> +({ \
> + __label__ __out; \
> + int __ret = -EFAULT; \
> + \
> + if (pin_user_pages_fast((unsigned long)(_self), 1, 0, &(_pagep)) != 1) \
> + goto __out; \
> + \
> + if (!PageAnon(_pagep) || \
> + get_user(_member, &(_self)->_member)) { \

Here should be 'get_user(_member, &(_self)->##_member))'
if I am not wrong.

> + unpin_user_page(_pagep); \
> + goto __out; \
> + } \
> + __ret = 0; \
> +__out: __ret; \
> +})

[...]

> +
> +/*
> + * Enqueue @tsk on it's server's runnable list
> + *
> + * Must be called in umcg_pin_pages() context, relies on tsk->umcg_server.
> + *
> + * cmpxchg based single linked list add such that list integrity is never
> + * violated. Userspace *MUST* remove it from the list before changing ->state.
> + * As such, we must change state to RUNNABLE before enqueue.
> + *
> + * Returns:
> + * 0: success
> + * -EFAULT
> + */
> +static int umcg_enqueue_runnable(struct task_struct *tsk)
> +{
> + struct umcg_task __user *server = tsk->umcg_server_task;
> + struct umcg_task __user *self = tsk->umcg_task;
> + u64 first_ptr, *head = &server->runnable_workers_ptr;
> + u64 self_ptr = (unsigned long)self;

Why not 'u64 self_ptr = (u64)self;' ?

> + /*
> + * umcg_pin_pages() did access_ok() on both pointers, use self here
> + * only because __user_access_begin() isn't available in generic code.
> + */
> + if (!user_access_begin(self, sizeof(*self)))
> + return -EFAULT;
> +
> + unsafe_get_user(first_ptr, head, Efault);
> + do {
> + unsafe_put_user(first_ptr, &self->runnable_workers_ptr, Efault);
> + } while (!unsafe_try_cmpxchg_user(head, &first_ptr, self_ptr, Efault));
> +
> + user_access_end();
> + return 0;
> +
> +Efault:
> + user_access_end();
> + return -EFAULT;
> +}

[...]

> +/*
> + * Handles ::next_tid as per sys_umcg_wait().
> + *
> + * ::next_tid - return
> + * -----------------------------
> + * 0 - 0 (success)
> + *
> + * tid - -ESRCH (no such task, or not of this UMCG)
> + * - -EAGAIN (next::state != RUNNABLE)
> + * - 0 (success, ::next_tid |= RUNNING)
> + *
> + * tid|RUNNING - -EAGAIN (next::state != RUNNING)
> + * - 0 (success)
> + *
> + * Returns:
> + * 0: success
> + * -EFAULT
> + * -ESRCH
> + * -EAGAIN
> + */
> +static int umcg_wake_next(struct task_struct *tsk, struct umcg_task __user *self)

@tsk is not used in function.

> +{
> + struct umcg_task __user *next_task;
> + struct task_struct *next;
> + u32 next_tid, state;
> + int ret;
> +
> + if (get_user(next_tid, &self->next_tid))
> + return -EFAULT;
> +
> + if (!next_tid)
> + return 0;
> +
> + next = umcg_get_task(next_tid);
> + if (!next)
> + return -ESRCH;
> +
> + next_task = READ_ONCE(next->umcg_task);
> +
> + if (next_tid & UMCG_TID_RUNNING) {
> + ret = -EFAULT;
> + if (get_user(state, &next_task->state))
> + goto put_next;
> +
> + ret = 0;
> + if ((state & UMCG_TASK_MASK) != UMCG_TASK_RUNNING)
> + ret = -EAGAIN;
> +
> + } else {
> + ret = umcg_wake_task(next, next_task);
> + if (ret)
> + goto put_next;
> +
> + ret = -EFAULT;
> + if (put_user(next_tid | UMCG_TID_RUNNING, &self->next_tid))
> + goto put_next;
> +
> + /*
> + * If this is a worker doing sys_umcg_wait() switching to
> + * another worker, userspace has the responsibility to update
> + * server::next_tid.
> + */
> +
> + ret = 0;
> + }
> +
> +put_next:
> + put_task_struct(next);
> + return ret;
> +}
> +