Commit 710da3c8 authored by Juri Lelli's avatar Juri Lelli Committed by Ingo Molnar

sched/core: Prevent race condition between cpuset and __sched_setscheduler()

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 cpuset_rwsem read lock from core scheduler, so to prevent
situations such as the one described above from happening.

The only exception is normalize_rt_tasks() which needs to work under
tasklist_lock and can't therefore grab cpuset_rwsem. We are fine with
this, as this function is only called by sysrq and, if that gets
triggered, DEADLINE guarantees are already gone out of the window
anyway.
Tested-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bristot@redhat.com
Cc: claudio@evidence.eu.com
Cc: lizefan@huawei.com
Cc: longman@redhat.com
Cc: luca.abeni@santannapisa.it
Cc: mathieu.poirier@linaro.org
Cc: rostedt@goodmis.org
Cc: tj@kernel.org
Cc: tommaso.cucinotta@santannapisa.it
Link: https://lkml.kernel.org/r/20190719140000.31694-9-juri.lelli@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1a763fd7
......@@ -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_lock(void);
extern void cpuset_read_unlock(void);
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 +178,9 @@ static inline void cpuset_update_active_cpus(void)
static inline void cpuset_wait_for_hotplug(void) { }
static inline void cpuset_read_lock(void) { }
static inline void cpuset_read_unlock(void) { }
static inline void cpuset_cpus_allowed(struct task_struct *p,
struct cpumask *mask)
{
......
......@@ -334,6 +334,17 @@ static struct cpuset top_cpuset = {
*/
DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
void cpuset_read_lock(void)
{
percpu_down_read(&cpuset_rwsem);
}
void cpuset_read_unlock(void)
{
percpu_up_read(&cpuset_rwsem);
}
static DEFINE_SPINLOCK(callback_lock);
static struct workqueue_struct *cpuset_migrate_mm_wq;
......
......@@ -4698,6 +4698,9 @@ static int __sched_setscheduler(struct task_struct *p,
return retval;
}
if (pi)
cpuset_read_lock();
/*
* Make sure no PI-waiters arrive (or leave) while we are
* changing the priority of the task:
......@@ -4772,6 +4775,8 @@ static int __sched_setscheduler(struct task_struct *p,
if (unlikely(oldpolicy != -1 && oldpolicy != p->policy)) {
policy = oldpolicy = -1;
task_rq_unlock(rq, p, &rf);
if (pi)
cpuset_read_unlock();
goto recheck;
}
......@@ -4832,8 +4837,10 @@ static int __sched_setscheduler(struct task_struct *p,
preempt_disable();
task_rq_unlock(rq, p, &rf);
if (pi)
if (pi) {
cpuset_read_unlock();
rt_mutex_adjust_pi(p);
}
/* Run balance callbacks after we've adjusted the PI chain: */
balance_callback(rq);
......@@ -4843,6 +4850,8 @@ static int __sched_setscheduler(struct task_struct *p,
unlock:
task_rq_unlock(rq, p, &rf);
if (pi)
cpuset_read_unlock();
return retval;
}
......@@ -4927,10 +4936,15 @@ do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
rcu_read_lock();
retval = -ESRCH;
p = find_process_by_pid(pid);
if (p != NULL)
retval = sched_setscheduler(p, policy, &lparam);
if (likely(p))
get_task_struct(p);
rcu_read_unlock();
if (likely(p)) {
retval = sched_setscheduler(p, policy, &lparam);
put_task_struct(p);
}
return retval;
}
......
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