On 11/24/20 15:50, Will Deacon wrote:
[...]
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index d2003a7d5ab5..818c8f7bdf2a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1860,24 +1860,18 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
> }
>
> /*
> - * Change a given task's CPU affinity. Migrate the thread to a
> - * proper CPU and schedule it away if the CPU it's executing on
> - * is removed from the allowed bitmask.
> - *
> - * NOTE: the caller must have a valid reference to the task, the
> - * task must not exit() & deallocate itself prematurely. The
> - * call is not atomic; no spinlocks may be held.
> + * Called with both p->pi_lock and rq->lock held; drops both before returning.
nit: wouldn't it be better for the caller to acquire and release the locks?
Not a big deal but it's always confusing when half of the work done outside the
function and the other half done inside.
Thanks
--
Qais Yousef
> */
> -static int __set_cpus_allowed_ptr(struct task_struct *p,
> - const struct cpumask *new_mask, bool check)
> +static int __set_cpus_allowed_ptr_locked(struct task_struct *p,
> + const struct cpumask *new_mask,
> + bool check,
> + struct rq *rq,
> + struct rq_flags *rf)
> {
> const struct cpumask *cpu_valid_mask = cpu_active_mask;
> unsigned int dest_cpu;
> - struct rq_flags rf;
> - struct rq *rq;
> int ret = 0;
>
> - rq = task_rq_lock(p, &rf);
> update_rq_clock(rq);
>
> if (p->flags & PF_KTHREAD) {
> @@ -1929,7 +1923,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
> if (task_running(rq, p) || p->state == TASK_WAKING) {
> struct migration_arg arg = { p, dest_cpu };
> /* Need help from migration thread: drop lock and wait. */
> - task_rq_unlock(rq, p, &rf);
> + task_rq_unlock(rq, p, rf);
> stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
> return 0;
> } else if (task_on_rq_queued(p)) {
> @@ -1937,20 +1931,69 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
> * OK, since we're going to drop the lock immediately
> * afterwards anyway.
> */
> - rq = move_queued_task(rq, &rf, p, dest_cpu);
> + rq = move_queued_task(rq, rf, p, dest_cpu);
> }
> out:
> - task_rq_unlock(rq, p, &rf);
> + task_rq_unlock(rq, p, rf);
>
> return ret;
> }
