On Fri, Jul 30, 2021 at 12:24:35PM +0100, Will Deacon wrote:
> @@ -2783,20 +2778,173 @@ static int __set_cpus_allowed_ptr(struct task_struct *p,
>
> __do_set_cpus_allowed(p, new_mask, flags);
>
> - return affine_move_task(rq, p, &rf, dest_cpu, flags);
> + if (flags & SCA_USER)
> + release_user_cpus_ptr(p);
> +
> + return affine_move_task(rq, p, rf, dest_cpu, flags);
>
> out:
> - task_rq_unlock(rq, p, &rf);
> + task_rq_unlock(rq, p, rf);
>
> return ret;
> }
> +void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
> +{
> + unsigned long flags;
> + struct cpumask *mask = p->user_cpus_ptr;
> +
> + /*
> + * Try to restore the old affinity mask. If this fails, then
> + * we free the mask explicitly to avoid it being inherited across
> + * a subsequent fork().
> + */
> + if (!mask || !__sched_setaffinity(p, mask))
> + return;
> +
> + raw_spin_lock_irqsave(&p->pi_lock, flags);
> + release_user_cpus_ptr(p);
> + raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> +}
Both these are a problem on RT.
The easiest recourse is simply never freeing the CPU mask (except on
exit). The alternative is something like the below I suppose..
I'm leaning towards the former option, wdyt?
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2733,6 +2733,7 @@ static int __set_cpus_allowed_ptr_locked
const struct cpumask *cpu_allowed_mask = task_cpu_possible_mask(p);
const struct cpumask *cpu_valid_mask = cpu_active_mask;
bool kthread = p->flags & PF_KTHREAD;
+ struct cpumask *user_mask = NULL;
unsigned int dest_cpu;
int ret = 0;
@@ -2792,9 +2793,13 @@ static int __set_cpus_allowed_ptr_locked
__do_set_cpus_allowed(p, new_mask, flags);
if (flags & SCA_USER)
- release_user_cpus_ptr(p);
+ swap(user_mask, p->user_cpus_ptr);
+
+ ret = affine_move_task(rq, p, rf, dest_cpu, flags);
+
+ kfree(user_mask);
- return affine_move_task(rq, p, rf, dest_cpu, flags);
+ return ret;
out:
task_rq_unlock(rq, p, rf);
@@ -2954,8 +2959,10 @@ void relax_compatible_cpus_allowed_ptr(s
return;
raw_spin_lock_irqsave(&p->pi_lock, flags);
- release_user_cpus_ptr(p);
+ p->user_cpus_ptr = NULL;
raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+
+ kfree(mask);
}
void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
