aboutsummaryrefslogtreecommitdiff
path: root/kernel/cpuset.c
diff options
context:
space:
mode:
authorOleg Nesterov <oleg@redhat.com>2010-03-15 10:10:27 +0100
committerIngo Molnar <mingo@elte.hu>2010-04-02 20:12:03 +0200
commit9084bb8246ea935b98320554229e2f371f7f52fa (patch)
tree8478d18125e3b4a7e0a31d702647dee1830d23ef /kernel/cpuset.c
parent6a1bdc1b577ebcb65f6603c57f8347309bc4ab13 (diff)
downloadlinux-2.6.34-ux500-9084bb8246ea935b98320554229e2f371f7f52fa.tar.gz
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>
Diffstat (limited to 'kernel/cpuset.c')
-rw-r--r--kernel/cpuset.c42
1 files changed, 42 insertions, 0 deletions
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 9a747f56d58..9a50c5f6e72 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2188,6 +2188,48 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
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)
{
nodes_setall(current->mems_allowed);