From: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx> 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> --- v4->v5: grab callback_lock instead of cpuset_mutex, as callback_lock is enough to get read-only access to cpusets [1] and it can be easily converted to be a raw_spinlock (done in previous - new - patch). [1] https://elixir.bootlin.com/linux/latest/source/kernel/cgroup/cpuset.c#L275 --- include/linux/cpuset.h | 6 ++++++ kernel/cgroup/cpuset.c | 18 ++++++++++++++++++ kernel/sched/core.c | 10 ++++++++++ 3 files changed, 34 insertions(+) diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index 934633a05d20..8e5a8dd0622b 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(void); +extern void cpuset_read_only_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 +178,10 @@ static inline void cpuset_update_active_cpus(void) static inline void cpuset_wait_for_hotplug(void) { } +static inline void cpuset_read_only_lock(void) { } + +static inline void cpuset_read_only_unlock(void) { } + 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 5b43f482fa0f..8dc26005bb1e 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2410,6 +2410,24 @@ void __init cpuset_init_smp(void) BUG_ON(!cpuset_migrate_mm_wq); } +/** + * cpuset_read_only_lock - Grab the callback_lock from another subsysytem + * + * Description: Gives the holder read-only access to cpusets. + */ +void cpuset_read_only_lock(void) +{ + raw_spin_lock(&callback_lock); +} + +/** + * cpuset_read_only_unlock - Release the callback_lock from another subsysytem + */ +void cpuset_read_only_unlock(void) +{ + raw_spin_unlock(&callback_lock); +} + /** * 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 22f5622cba69..ac11ee599968 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4228,6 +4228,13 @@ static int __sched_setscheduler(struct task_struct *p, rq = task_rq_lock(p, &rf); update_rq_clock(rq); + /* + * 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(); + /* * Changing the policy of the stop threads its a very bad idea: */ @@ -4289,6 +4296,7 @@ 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; + cpuset_read_only_unlock(); task_rq_unlock(rq, p, &rf); goto recheck; } @@ -4346,6 +4354,7 @@ static int __sched_setscheduler(struct task_struct *p, /* Avoid rq from going away on us: */ preempt_disable(); + cpuset_read_only_unlock(); task_rq_unlock(rq, p, &rf); if (pi) @@ -4358,6 +4367,7 @@ static int __sched_setscheduler(struct task_struct *p, return 0; unlock: + cpuset_read_only_unlock(); task_rq_unlock(rq, p, &rf); return retval; } -- 2.17.1
