sched: Make select_fallback_rq() cpuset friendly
Introduce cpuset_cpus_allowed_fallback() helper to fix the cpuset problems with select_fallback_rq(). It can be called from any context and can't use any cpuset locks including task_lock(). It is called when the task doesn't have online cpus in ->cpus_allowed but ttwu/etc must be able to find a suitable cpu. I am not proud of this patch. Everything which needs such a fat comment can't be good even if correct. But I'd prefer to not change the locking rules in the code I hardly understand, and in any case I believe this simple change make the code much more correct compared to deadlocks we currently have. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20100315091027.GA9155@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
parent
6a1bdc1b57
commit
9084bb8246
|
@ -21,6 +21,7 @@ extern int number_of_cpusets; /* How many cpusets are defined in system? */
|
||||||
extern int cpuset_init(void);
|
extern int cpuset_init(void);
|
||||||
extern void cpuset_init_smp(void);
|
extern void cpuset_init_smp(void);
|
||||||
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
|
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
|
||||||
|
extern int cpuset_cpus_allowed_fallback(struct task_struct *p);
|
||||||
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
|
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
|
||||||
#define cpuset_current_mems_allowed (current->mems_allowed)
|
#define cpuset_current_mems_allowed (current->mems_allowed)
|
||||||
void cpuset_init_current_mems_allowed(void);
|
void cpuset_init_current_mems_allowed(void);
|
||||||
|
@ -101,6 +102,12 @@ static inline void cpuset_cpus_allowed(struct task_struct *p,
|
||||||
cpumask_copy(mask, cpu_possible_mask);
|
cpumask_copy(mask, cpu_possible_mask);
|
||||||
}
|
}
|
||||||
|
|
||||||
|
static inline int cpuset_cpus_allowed_fallback(struct task_struct *p)
|
||||||
|
{
|
||||||
|
cpumask_copy(&p->cpus_allowed, cpu_possible_mask);
|
||||||
|
return cpumask_any(cpu_active_mask);
|
||||||
|
}
|
||||||
|
|
||||||
static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
|
static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
|
||||||
{
|
{
|
||||||
return node_possible_map;
|
return node_possible_map;
|
||||||
|
|
|
@ -2188,6 +2188,48 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
|
||||||
mutex_unlock(&callback_mutex);
|
mutex_unlock(&callback_mutex);
|
||||||
}
|
}
|
||||||
|
|
||||||
|
int cpuset_cpus_allowed_fallback(struct task_struct *tsk)
|
||||||
|
{
|
||||||
|
const struct cpuset *cs;
|
||||||
|
int cpu;
|
||||||
|
|
||||||
|
rcu_read_lock();
|
||||||
|
cs = task_cs(tsk);
|
||||||
|
if (cs)
|
||||||
|
cpumask_copy(&tsk->cpus_allowed, cs->cpus_allowed);
|
||||||
|
rcu_read_unlock();
|
||||||
|
|
||||||
|
/*
|
||||||
|
* We own tsk->cpus_allowed, nobody can change it under us.
|
||||||
|
*
|
||||||
|
* But we used cs && cs->cpus_allowed lockless and thus can
|
||||||
|
* race with cgroup_attach_task() or update_cpumask() and get
|
||||||
|
* the wrong tsk->cpus_allowed. However, both cases imply the
|
||||||
|
* subsequent cpuset_change_cpumask()->set_cpus_allowed_ptr()
|
||||||
|
* which takes task_rq_lock().
|
||||||
|
*
|
||||||
|
* If we are called after it dropped the lock we must see all
|
||||||
|
* changes in tsk_cs()->cpus_allowed. Otherwise we can temporary
|
||||||
|
* set any mask even if it is not right from task_cs() pov,
|
||||||
|
* the pending set_cpus_allowed_ptr() will fix things.
|
||||||
|
*/
|
||||||
|
|
||||||
|
cpu = cpumask_any_and(&tsk->cpus_allowed, cpu_active_mask);
|
||||||
|
if (cpu >= nr_cpu_ids) {
|
||||||
|
/*
|
||||||
|
* Either tsk->cpus_allowed is wrong (see above) or it
|
||||||
|
* is actually empty. The latter case is only possible
|
||||||
|
* if we are racing with remove_tasks_in_empty_cpuset().
|
||||||
|
* Like above we can temporary set any mask and rely on
|
||||||
|
* set_cpus_allowed_ptr() as synchronization point.
|
||||||
|
*/
|
||||||
|
cpumask_copy(&tsk->cpus_allowed, cpu_possible_mask);
|
||||||
|
cpu = cpumask_any(cpu_active_mask);
|
||||||
|
}
|
||||||
|
|
||||||
|
return cpu;
|
||||||
|
}
|
||||||
|
|
||||||
void cpuset_init_current_mems_allowed(void)
|
void cpuset_init_current_mems_allowed(void)
|
||||||
{
|
{
|
||||||
nodes_setall(current->mems_allowed);
|
nodes_setall(current->mems_allowed);
|
||||||
|
|
|
@ -2300,9 +2300,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
|
||||||
|
|
||||||
/* No more Mr. Nice Guy. */
|
/* No more Mr. Nice Guy. */
|
||||||
if (unlikely(dest_cpu >= nr_cpu_ids)) {
|
if (unlikely(dest_cpu >= nr_cpu_ids)) {
|
||||||
cpumask_copy(&p->cpus_allowed, cpu_possible_mask);
|
dest_cpu = cpuset_cpus_allowed_fallback(p);
|
||||||
dest_cpu = cpumask_any(cpu_active_mask);
|
|
||||||
|
|
||||||
/*
|
/*
|
||||||
* Don't tell them about moving exiting tasks or
|
* Don't tell them about moving exiting tasks or
|
||||||
* kernel threads (both mm NULL), since they never
|
* kernel threads (both mm NULL), since they never
|
||||||
|
|
Loading…
Reference in a new issue