Re: [PATCH v11 08/16] sched: Allow task CPU affinity to be restricted on asymmetric systems
From: Peter Zijlstra <peterz@infradead.org>
Date: 2021-08-17 15:11:20
Also in:
linux-arm-kernel, lkml
On Fri, Jul 30, 2021 at 12:24:35PM +0100, Will Deacon wrote:
quoted hunk ↗ jump to hunk
@@ -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)