From 3bd3706251ee8ab67e69d9340ac2abdca217e733 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Tue, 23 Apr 2019 16:26:36 +0200 Subject: sched/core: Provide a pointer to the valid CPU mask In commit: 4b53a3412d66 ("sched/core: Remove the tsk_nr_cpus_allowed() wrapper") the tsk_nr_cpus_allowed() wrapper was removed. There was not much difference in !RT but in RT we used this to implement migrate_disable(). Within a migrate_disable() section the CPU mask is restricted to single CPU while the "normal" CPU mask remains untouched. As an alternative implementation Ingo suggested to use: struct task_struct { const cpumask_t *cpus_ptr; cpumask_t cpus_mask; }; with t->cpus_ptr = &t->cpus_mask; In -RT we then can switch the cpus_ptr to: t->cpus_ptr = &cpumask_of(task_cpu(p)); in a migration disabled region. The rules are simple: - Code that 'uses' ->cpus_allowed would use the pointer. - Code that 'modifies' ->cpus_allowed would use the direct mask. Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thomas Gleixner Cc: Linus Torvalds Cc: Peter Zijlstra Link: https://lkml.kernel.org/r/20190423142636.14347-1-bigeasy@linutronix.de Signed-off-by: Ingo Molnar --- arch/ia64/kernel/mca.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/ia64') diff --git a/arch/ia64/kernel/mca.c b/arch/ia64/kernel/mca.c index 6a52d761854b..79190d877fa7 100644 --- a/arch/ia64/kernel/mca.c +++ b/arch/ia64/kernel/mca.c @@ -1831,7 +1831,7 @@ format_mca_init_stack(void *mca_data, unsigned long offset, ti->cpu = cpu; p->stack = ti; p->state = TASK_UNINTERRUPTIBLE; - cpumask_set_cpu(cpu, &p->cpus_allowed); + cpumask_set_cpu(cpu, &p->cpus_mask); INIT_LIST_HEAD(&p->tasks); p->parent = p->real_parent = p->group_leader = p; INIT_LIST_HEAD(&p->children); -- cgit v1.2.3-55-g7522