No synchronisation mechanism exists between the cpuset subsystem and calls
to function __sched_setscheduler(). As such, it is possible that new root
domains are created on the cpuset side while a deadline acceptance test
is carried out in __sched_setscheduler(), leading to a potential oversell
of CPU bandwidth.
Grab callback_lock from core scheduler, so to prevent situations such as
the one described above from happening.
Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
---
v6->v7: take cpuset_read_only_lock before rq and pi locks, as to not
introdue an unwanted dependency between the former and the
latters (peterz)
---
include/linux/cpuset.h | 14 ++++++++++++++
kernel/cgroup/cpuset.c | 27 ++++++++++++++++++++++++++-
kernel/sched/core.c | 27 ++++++++++++++++++++++-----
3 files changed, 62 insertions(+), 6 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 934633a05d20..34c58c4dd445 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -55,6 +55,8 @@ extern void cpuset_init_smp(void);
extern void cpuset_force_rebuild(void);
extern void cpuset_update_active_cpus(void);
extern void cpuset_wait_for_hotplug(void);
+extern void cpuset_read_only_lock(unsigned long *flags);
+extern void cpuset_read_only_unlock(unsigned long *flags);
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
@@ -176,6 +178,18 @@ static inline void cpuset_update_active_cpus(void)
static inline void cpuset_wait_for_hotplug(void) { }
+static inline void cpuset_read_only_lock(unsigned long *flags)
+{
+ local_irq_save(*flags);
+ preempt_disable();
+}
+
+static inline void cpuset_read_only_unlock(unsigned long *flags)
+{
+ local_irq_restore(*flags);
+ preempt_enable();
+}
+
static inline void cpuset_cpus_allowed(struct task_struct *p,
struct cpumask *mask)
{
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index ff9bd5abe613..ca5364f037a1 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -318,7 +318,8 @@ static struct cpuset top_cpuset = {
* __alloc_pages().
*
* If a task is only holding callback_lock, then it has read-only
- * access to cpusets.
+ * access to cpusets. Mind that callback_lock might be grabbed from other
+ * subsystems as well (via cpuset_read_only_lock()).
*
* Now, the task_struct fields mems_allowed and mempolicy may be changed
* by other task, we use alloc_lock in the task_struct fields to protect
@@ -3233,6 +3234,30 @@ void __init cpuset_init_smp(void)
BUG_ON(!cpuset_migrate_mm_wq);
}
+/**
+ * cpuset_read_only_lock - Grab the callback_lock from cpuset subsystem.
+ *
+ * Description: As described in full details the comment above cpuset_mutex
+ * and callback_lock definitions, holding callback_lock gives the holder
+ * read-only access to cpusets. Even though it might look counter-intuitive
+ * (as callback_lock is a spinlock), in fact a task must hold both
+ * callback_lock _and_ cpuset_mutex to modify cpusets (write access).
+ */
+void cpuset_read_only_lock(unsigned long *flags)
+ __acquires(&callback_lock)
+{
+ raw_spin_lock_irqsave(&callback_lock, *flags);
+}
+
+/**
+ * cpuset_read_only_unlock - Release the callback_lock from cpuset subsystem.
+ */
+void cpuset_read_only_unlock(unsigned long *flags)
+ __releases(&callback_lock)
+{
+ raw_spin_unlock_irqrestore(&callback_lock, *flags);
+}
+
/**
* cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset.
* @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 98e835de1e7b..543eb31aa243 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4260,14 +4260,25 @@ static int __sched_setscheduler(struct task_struct *p,
return retval;
}
+ /*
+ * Make sure we don't race with the cpuset subsystem where root
+ * domains can be rebuilt or modified while operations like DL
+ * admission checks are carried out.
+ */
+ cpuset_read_only_lock(&rf.flags);
+
/*
* Make sure no PI-waiters arrive (or leave) while we are
* changing the priority of the task:
- *
+ */
+
+ raw_spin_lock(&p->pi_lock);
+
+ /*
* To be able to change p->policy safely, the appropriate
* runqueue lock must be held.
*/
- rq = task_rq_lock(p, &rf);
+ rq = __task_rq_lock(p, &rf);
update_rq_clock(rq);
/*
@@ -4331,7 +4342,9 @@ static int __sched_setscheduler(struct task_struct *p,
/* Re-check policy now with rq lock held: */
if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
policy = oldpolicy = -1;
- task_rq_unlock(rq, p, &rf);
+ __task_rq_unlock(rq, &rf);
+ raw_spin_unlock(&p->pi_lock);
+ cpuset_read_only_unlock(&rf.flags);
goto recheck;
}
@@ -4388,7 +4401,9 @@ static int __sched_setscheduler(struct task_struct *p,
/* Avoid rq from going away on us: */
preempt_disable();
- task_rq_unlock(rq, p, &rf);
+ __task_rq_unlock(rq, &rf);
+ raw_spin_unlock(&p->pi_lock);
+ cpuset_read_only_unlock(&rf.flags);
if (pi)
rt_mutex_adjust_pi(p);
@@ -4400,7 +4415,9 @@ static int __sched_setscheduler(struct task_struct *p,
return 0;
unlock:
- task_rq_unlock(rq, p, &rf);
+ __task_rq_unlock(rq, &rf);
+ raw_spin_unlock(&p->pi_lock);
+ cpuset_read_only_unlock(&rf.flags);
return retval;
}
--
2.17.2
