On Mon, Aug 05, 2019 at 01:53:09PM +0200, Peter Zijlstra wrote: > > Like so? >
Yes, that's exactly what I meant! What about this refactoring? Thanks, Alessio --- >From 459d5488acb3fac938b0f35f480a81a6e401ef92 Mon Sep 17 00:00:00 2001 From: Alessio Balsini <bals...@android.com> Date: Thu, 22 Aug 2019 12:55:55 +0100 Subject: [PATCH] sched/deadline: Impose global limits on sched_attr::sched_period There are two DoS scenarios with SCHED_DEADLINE related to sched_attr::sched_period: - since access-control only looks at utilization and density, a very large period can allow a very large runtime, which in turn can incur a very large latency to lower priority tasks. - for very short periods we can end up spending more time programming the hardware timer than actually running the task. Mitigate these by imposing limits on the period. Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Signed-off-by: Alessio Balsini <bals...@android.com> --- include/linux/sched/sysctl.h | 7 +++++ kernel/sched/deadline.c | 51 ++++++++++++++++++++++++++++++++++-- kernel/sysctl.c | 14 ++++++++++ 3 files changed, 70 insertions(+), 2 deletions(-) diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h index d4f6215ee03f7..7c8ef07e52133 100644 --- a/include/linux/sched/sysctl.h +++ b/include/linux/sched/sysctl.h @@ -56,6 +56,13 @@ int sched_proc_update_handler(struct ctl_table *table, int write, extern unsigned int sysctl_sched_rt_period; extern int sysctl_sched_rt_runtime; +extern unsigned int sysctl_sched_dl_period_max; +extern unsigned int sysctl_sched_dl_period_min; + +extern int sched_dl_period_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos); + #ifdef CONFIG_UCLAMP_TASK extern unsigned int sysctl_sched_uclamp_util_min; extern unsigned int sysctl_sched_uclamp_util_max; diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 0b9cbfb2b1d4f..fcdf70d9c0516 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2640,6 +2640,42 @@ void __getparam_dl(struct task_struct *p, struct sched_attr *attr) attr->sched_flags = dl_se->flags; } +/* + * Default limits for DL period: on the top end we guard against small util + * tasks still getting ridiculous long effective runtimes, on the bottom end we + * guard against timer DoS. + */ +unsigned int sysctl_sched_dl_period_max = 1 << 22; /* ~4 seconds */ +unsigned int sysctl_sched_dl_period_min = 100; /* 100 us */ + +int sched_dl_period_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos) +{ + unsigned int old_max, old_min; + static DEFINE_MUTEX(mutex); + int ret; + + mutex_lock(&mutex); + old_max = sysctl_sched_dl_period_max; + old_min = sysctl_sched_dl_period_min; + + ret = proc_douintvec(table, write, buffer, lenp, ppos); + if (!ret && write) { + u64 max = (u64)sysctl_sched_dl_period_max * NSEC_PER_USEC; + u64 min = (u64)sysctl_sched_dl_period_min * NSEC_PER_USEC; + + if (min < 1ULL << DL_SCALE || max < min) { + sysctl_sched_dl_period_max = old_max; + sysctl_sched_dl_period_min = old_min; + ret = -EINVAL; + } + } + mutex_unlock(&mutex); + + return ret; +} + /* * This function validates the new parameters of a -deadline task. * We ask for the deadline not being zero, and greater or equal @@ -2652,6 +2688,8 @@ void __getparam_dl(struct task_struct *p, struct sched_attr *attr) */ bool __checkparam_dl(const struct sched_attr *attr) { + u64 period, max, min; + /* special dl tasks don't actually use any parameter */ if (attr->sched_flags & SCHED_FLAG_SUGOV) return true; @@ -2675,12 +2713,21 @@ bool __checkparam_dl(const struct sched_attr *attr) attr->sched_period & (1ULL << 63)) return false; + period = attr->sched_period; + if (!period) + period = attr->sched_deadline; + /* runtime <= deadline <= period (if period != 0) */ - if ((attr->sched_period != 0 && - attr->sched_period < attr->sched_deadline) || + if (period < attr->sched_deadline || attr->sched_deadline < attr->sched_runtime) return false; + max = (u64)READ_ONCE(sysctl_sched_dl_period_max) * NSEC_PER_USEC; + min = (u64)READ_ONCE(sysctl_sched_dl_period_min) * NSEC_PER_USEC; + + if (period < min || period > max) + return false; + return true; } diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 078950d9605ba..0d07e4707e9d2 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -442,6 +442,20 @@ static struct ctl_table kern_table[] = { .mode = 0644, .proc_handler = sched_rt_handler, }, + { + .procname = "sched_deadline_period_max_us", + .data = &sysctl_sched_dl_period_max, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = sched_dl_period_handler, + }, + { + .procname = "sched_deadline_period_min_us", + .data = &sysctl_sched_dl_period_min, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = sched_dl_period_handler, + }, { .procname = "sched_rr_timeslice_ms", .data = &sysctl_sched_rr_timeslice, -- 2.23.0.187.g17f5b7556c-goog