set_cpus_allowed_ptr() modifies the allowed cpu mask of a task. The
function performs the following checks before applying new mask.
* Check whether PF_THREAD_BOUND is set. This is set for bound
kthreads so that they can't be moved around.
* Check whether the target cpu is still marked active - cpu_active().
Active state is cleared early while downing a cpu.
This patch adds force_cpus_allowed() which bypasses the above two
checks. The caller is responsible for guaranteeing that the
destination cpu doesn't go down until force_cpus_allowed() finishes.
The first check is bypassed by factoring out actual migration part
into __set_cpus_allowed() from set_cpus_allowed_ptr() and calling the
inner function from force_cpus_allowed().
The second check is buried deep down in __migrate_task() which is
executed by migration threads. @force parameter is added to
__migrate_task(). As the only way to pass parameters from
__set_cpus_allowed() is through migration_req, migration_req->force is
added and the @force parameter is passed down to __migrate_task().
Please note the naming discrepancy between set_cpus_allowed_ptr() and
the new functions. The _ptr suffix is from the days when cpumask api
wasn't mature and future changes should drop it from
set_cpus_allowed_ptr() too.
force_cpus_allowed() will be used for concurrency-managed workqueue.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
---
include/linux/sched.h | 7 ++++
kernel/sched.c | 89 +++++++++++++++++++++++++++++++++----------------
2 files changed, 67 insertions(+), 29 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c889a58..82544e8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1851,6 +1851,8 @@ static inline void rcu_copy_process(struct task_struct *p)
#ifdef CONFIG_SMP
extern int set_cpus_allowed_ptr(struct task_struct *p,
const struct cpumask *new_mask);
+extern int force_cpus_allowed(struct task_struct *p,
+ const struct cpumask *new_mask);
#else
static inline int set_cpus_allowed_ptr(struct task_struct *p,
const struct cpumask *new_mask)
@@ -1859,6 +1861,11 @@ static inline int set_cpus_allowed_ptr(struct task_struct *p,
return -EINVAL;
return 0;
}
+static inline int force_cpus_allowed(struct task_struct *p,
+ const struct cpumask *new_mask)
+{
+ return set_cpus_allowed_ptr(p, new_mask);
+}
#endif
#ifndef CONFIG_CPUMASK_OFFSTACK
diff --git a/kernel/sched.c b/kernel/sched.c
index bad92c0..eaa660f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2107,6 +2107,7 @@ struct migration_req {
struct task_struct *task;
int dest_cpu;
+ bool force;
struct completion done;
};
@@ -2115,8 +2116,8 @@ struct migration_req {
* The task's runqueue lock must be held.
* Returns true if you have to wait for migration thread.
*/
-static int
-migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
+static int migrate_task(struct task_struct *p, int dest_cpu,
+ struct migration_req *req, bool force)
{
struct rq *rq = task_rq(p);
@@ -2133,6 +2134,7 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
init_completion(&req->done);
req->task = p;
req->dest_cpu = dest_cpu;
+ req->force = force;
list_add(&req->list, &rq->migration_queue);
return 1;
@@ -3171,7 +3173,7 @@ static void sched_migrate_task(struct task_struct *p, int dest_cpu)
goto out;
/* force the process onto the specified CPU */
- if (migrate_task(p, dest_cpu, &req)) {
+ if (migrate_task(p, dest_cpu, &req, false)) {
/* Need to wait for migration thread (might exit: take ref). */
struct task_struct *mt = rq->migration_thread;
@@ -7099,34 +7101,19 @@ static inline void sched_init_granularity(void)
* 7) we wake up and the migration is done.
*/
-/*
- * Change a given task's CPU affinity. Migrate the thread to a
- * proper CPU and schedule it away if the CPU it's executing on
- * is removed from the allowed bitmask.
- *
- * NOTE: the caller must have a valid reference to the task, the
- * task must not exit() & deallocate itself prematurely. The
- * call is not atomic; no spinlocks may be held.
- */
-int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
+static inline int __set_cpus_allowed(struct task_struct *p,
+ const struct cpumask *new_mask,
+ struct rq *rq, unsigned long *flags,
+ bool force)
{
struct migration_req req;
- unsigned long flags;
- struct rq *rq;
int ret = 0;
- rq = task_rq_lock(p, &flags);
if (!cpumask_intersects(new_mask, cpu_online_mask)) {
ret = -EINVAL;
goto out;
}
- if (unlikely((p->flags & PF_THREAD_BOUND) && p != current &&
- !cpumask_equal(&p->cpus_allowed, new_mask))) {
- ret = -EINVAL;
- goto out;
- }
-
if (p->sched_class->set_cpus_allowed)
p->sched_class->set_cpus_allowed(p, new_mask);
else {
@@ -7138,12 +7125,13 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
if (cpumask_test_cpu(task_cpu(p), new_mask))
goto out;
- if (migrate_task(p, cpumask_any_and(cpu_online_mask, new_mask), &req)) {
+ if (migrate_task(p, cpumask_any_and(cpu_online_mask, new_mask), &req,
+ force)) {
/* Need help from migration thread: drop lock and wait. */
struct task_struct *mt = rq->migration_thread;
get_task_struct(mt);
- task_rq_unlock(rq, &flags);
+ task_rq_unlock(rq, flags);
wake_up_process(rq->migration_thread);
put_task_struct(mt);
wait_for_completion(&req.done);
@@ -7151,13 +7139,54 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
return 0;
}
out:
- task_rq_unlock(rq, &flags);
+ task_rq_unlock(rq, flags);
return ret;
}
+
+/*
+ * Change a given task's CPU affinity. Migrate the thread to a
+ * proper CPU and schedule it away if the CPU it's executing on
+ * is removed from the allowed bitmask.
+ *
+ * NOTE: the caller must have a valid reference to the task, the
+ * task must not exit() & deallocate itself prematurely. The
+ * call is not atomic; no spinlocks may be held.
+ */
+int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
+{
+ unsigned long flags;
+ struct rq *rq;
+
+ rq = task_rq_lock(p, &flags);
+
+ if (unlikely((p->flags & PF_THREAD_BOUND) && p != current &&
+ !cpumask_equal(&p->cpus_allowed, new_mask))) {
+ task_rq_unlock(rq, &flags);
+ return -EINVAL;
+ }
+
+ return __set_cpus_allowed(p, new_mask, rq, &flags, false);
+}
EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
/*
+ * Similar to set_cpus_allowed_ptr() but bypasses PF_THREAD_BOUND
+ * check and ignores cpu_active() status as long as the cpu is online.
+ * The caller is responsible for guaranteeing that the destination
+ * cpus don't go down until this function finishes and in general
+ * ensuring things don't go bonkers.
+ */
+int force_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
+{
+ unsigned long flags;
+ struct rq *rq;
+
+ rq = task_rq_lock(p, &flags);
+ return __set_cpus_allowed(p, new_mask, rq, &flags, true);
+}
+
+/*
* Move (not current) task off this cpu, onto dest cpu. We're doing
* this because either it can't run here any more (set_cpus_allowed()
* away from this CPU, or CPU going down), or because we're
@@ -7168,12 +7197,13 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
*
* Returns non-zero if task was successfully migrated.
*/
-static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
+static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu,
+ bool force)
{
struct rq *rq_dest, *rq_src;
int ret = 0, on_rq;
- if (unlikely(!cpu_active(dest_cpu)))
+ if (!force && unlikely(!cpu_active(dest_cpu)))
return ret;
rq_src = cpu_rq(src_cpu);
@@ -7252,7 +7282,8 @@ static int migration_thread(void *data)
if (req->task != NULL) {
spin_unlock(&rq->lock);
- __migrate_task(req->task, cpu, req->dest_cpu);
+ __migrate_task(req->task, cpu, req->dest_cpu,
+ req->force);
} else if (likely(cpu == (badcpu = smp_processor_id()))) {
req->dest_cpu = RCU_MIGRATION_GOT_QS;
spin_unlock(&rq->lock);
@@ -7277,7 +7308,7 @@ static int __migrate_task_irq(struct task_struct *p, int src_cpu, int dest_cpu)
int ret;
local_irq_disable();
- ret = __migrate_task(p, src_cpu, dest_cpu);
+ ret = __migrate_task(p, src_cpu, dest_cpu, false);
local_irq_enable();
return ret;
}
--
1.6.5.3
--
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