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SubjectRe: [PATCH v5 1/3] sched: Use user_cpus_ptr for saving user provided cpumask in sched_setaffinity()
On Tue, Aug 16, 2022 at 03:27:32PM -0400, Waiman Long wrote:
> @@ -2981,25 +2969,21 @@ static int restrict_cpus_allowed_ptr(struct task_struct *p,
> goto err_unlock;
> }
>
> - if (!cpumask_and(new_mask, &p->cpus_mask, subset_mask)) {
> +
> + if (p->user_cpus_ptr)
> + not_empty = cpumask_and(new_mask, p->user_cpus_ptr, subset_mask);
> + else
> + not_empty = cpumask_and(new_mask, cpu_online_mask, subset_mask);
> +
> + if (!not_empty) {
> err = -EINVAL;
> goto err_unlock;
> }
>
> - /*
> - * We're about to butcher the task affinity, so keep track of what
> - * the user asked for in case we're able to restore it later on.
> - */
> - if (user_mask) {
> - cpumask_copy(user_mask, p->cpus_ptr);
> - p->user_cpus_ptr = user_mask;
> - }
> -
> return __set_cpus_allowed_ptr_locked(p, new_mask, 0, rq, &rf);
>
> err_unlock:
> task_rq_unlock(rq, p, &rf);
> - kfree(user_mask);
> return err;
> }
>
> @@ -3049,34 +3033,27 @@ void force_compatible_cpus_allowed_ptr(struct task_struct *p)
> }
>
> static int
> -__sched_setaffinity(struct task_struct *p, const struct cpumask *mask);
> +__sched_setaffinity(struct task_struct *p, const struct cpumask *mask, bool save_mask);
>
> /*
> * Restore the affinity of a task @p which was previously restricted by a
> - * call to force_compatible_cpus_allowed_ptr(). This will clear (and free)
> - * @p->user_cpus_ptr.
> + * call to force_compatible_cpus_allowed_ptr().
> *
> * It is the caller's responsibility to serialise this with any calls to
> * force_compatible_cpus_allowed_ptr(@p).
> */
> void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
> {
> - struct cpumask *user_mask = p->user_cpus_ptr;
> - unsigned long flags;
> + const struct cpumask *user_mask = p->user_cpus_ptr;
> +
> + if (!user_mask)
> + user_mask = cpu_online_mask;
>
> /*
> - * 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().
> + * Try to restore the old affinity mask with __sched_setaffinity().
> + * Cpuset masking will be done there too.
> */
> - if (!user_mask || !__sched_setaffinity(p, user_mask))
> - return;
> -
> - raw_spin_lock_irqsave(&p->pi_lock, flags);
> - user_mask = clear_user_cpus_ptr(p);
> - raw_spin_unlock_irqrestore(&p->pi_lock, flags);
> -
> - kfree(user_mask);
> + __sched_setaffinity(p, user_mask, false);
> }
>
> void set_task_cpu(struct task_struct *p, unsigned int new_cpu)


Would it not be simpler to write it something like so?

---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 03053eebb22e..cdae4d50a588 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2955,7 +2955,6 @@ static int restrict_cpus_allowed_ptr(struct task_struct *p,
struct rq_flags rf;
struct rq *rq;
int err;
- bool not_empty;

rq = task_rq_lock(p, &rf);

@@ -2969,13 +2968,7 @@ static int restrict_cpus_allowed_ptr(struct task_struct *p,
goto err_unlock;
}

-
- if (p->user_cpus_ptr)
- not_empty = cpumask_and(new_mask, p->user_cpus_ptr, subset_mask);
- else
- not_empty = cpumask_and(new_mask, cpu_online_mask, subset_mask);
-
- if (!not_empty) {
+ if (!cpumask_and(new_mask, task_user_cpus(p), subset_mask)) {
err = -EINVAL;
goto err_unlock;
}
@@ -3044,16 +3037,11 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask, bool save
*/
void relax_compatible_cpus_allowed_ptr(struct task_struct *p)
{
- const struct cpumask *user_mask = p->user_cpus_ptr;
-
- if (!user_mask)
- user_mask = cpu_online_mask;
-
/*
* Try to restore the old affinity mask with __sched_setaffinity().
* Cpuset masking will be done there too.
*/
- __sched_setaffinity(p, user_mask, false);
+ __sched_setaffinity(p, task_user_cpus(p), false);
}

void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 15eefcd65faa..426e9b64b587 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1881,6 +1881,13 @@ static inline void dirty_sched_domain_sysctl(int cpu)
#endif

extern int sched_update_scaling(void);
+
+static inline const struct cpumask *task_user_cpus(struct task_struct *p)
+{
+ if (!p->user_cpus_ptr)
+ return cpus_possible_mask; /* &init_task.cpus_mask */
+ return p->user_cpus_ptr;
+}
#endif /* CONFIG_SMP */

#include "stats.h"
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