Messages in this thread | | | From | bsegall@google ... | Subject | Re: [PATCH] sched: Defend cfs and rt bandwidth quota against overflow | Date | Thu, 23 Apr 2020 13:33:33 -0700 |
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Huaixin Chang <changhuaixin@linux.alibaba.com> writes:
> When users write some huge number into cpu.cfs_quota_us or > cpu.rt_runtime_us, overflow might happen during to_ratio() shifts of > schedulable checks. > > to_ratio() could be altered to avoid unnecessary internal overflow, but > min_cfs_quota_period is less than 1 << BW_SHIFT, so a cutoff would still > be needed. Set a cap MAX_BW for cfs_quota_us and rt_runtime_us to > prevent overflow. > > Signed-off-by: Huaixin Chang <changhuaixin@linux.alibaba.com> > --- > kernel/sched/core.c | 8 ++++++++ > kernel/sched/rt.c | 9 +++++++++ > kernel/sched/sched.h | 2 ++ > 3 files changed, 19 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 3a61a3b8eaa9..0be1782e15c9 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7390,6 +7390,8 @@ static DEFINE_MUTEX(cfs_constraints_mutex); > > const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */ > static const u64 min_cfs_quota_period = 1 * NSEC_PER_MSEC; /* 1ms */ > +/* More than 203 days if BW_SHIFT equals 20. */ > +static const u64 max_cfs_runtime = MAX_BW * NSEC_PER_USEC; > > static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime); > > @@ -7417,6 +7419,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) > if (period > max_cfs_quota_period) > return -EINVAL; > > + /* > + * Bound quota to defend quota against overflow during bandwidth shift. > + */ > + if (quota != RUNTIME_INF && quota > max_cfs_runtime) > + return -EINVAL; > + > /* > * Prevent race between setting of cfs_rq->runtime_enabled and > * unthrottle_offline_cfs_rqs(). > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c > index df11d88c9895..7ba49625cdbd 100644 > --- a/kernel/sched/rt.c > +++ b/kernel/sched/rt.c > @@ -2569,6 +2569,9 @@ static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime) > return ret; > } > > +/* More than 4 hours if BW_SHIFT equals 20. */ > +static const u64 max_rt_runtime = MAX_BW; > + > static int tg_set_rt_bandwidth(struct task_group *tg, > u64 rt_period, u64 rt_runtime) > { > @@ -2585,6 +2588,12 @@ static int tg_set_rt_bandwidth(struct task_group *tg, > if (rt_period == 0) > return -EINVAL; > > + /* > + * Bound quota to defend quota against overflow during bandwidth shift. > + */ > + if (rt_runtime != RUNTIME_INF && rt_runtime > max_rt_runtime) > + return -EINVAL; > +
We probably _do_ also want this in sched_rt_global_validate now that I think of it. Other than missing that, it looks good.
> mutex_lock(&rt_constraints_mutex); > err = __rt_schedulable(tg, rt_period, rt_runtime); > if (err) > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h > index db3a57675ccf..1f58677a8f23 100644 > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1918,6 +1918,8 @@ extern void init_dl_inactive_task_timer(struct sched_dl_entity *dl_se); > #define BW_SHIFT 20 > #define BW_UNIT (1 << BW_SHIFT) > #define RATIO_SHIFT 8 > +#define MAX_BW_BITS (64 - BW_SHIFT) > +#define MAX_BW ((1ULL << MAX_BW_BITS) - 1) > unsigned long to_ratio(u64 period, u64 runtime); > > extern void init_entity_runnable_average(struct sched_entity *se);
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