[GIT PULL] scheduler fixes

Ingo Molnar
2013-11-13T20:15:13Z

Linus,

Please pull the latest sched-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

# HEAD: 85b088e934b9943322bfe37077289ae60f1b3414 sched/fair: Avoid integer overflow

Four bugfixes and one performance fix.

Thanks,

Ingo

------------------>
Michael wang (1):
sched: Fix endless sync_sched/rcu() loop inside _cpu_down()

Michal Nazarewicz (1):
sched/fair: Avoid integer overflow

Peter Zijlstra (2):
sched/numa: Cure update_numa_stats() vs. hotplug
sched: Optimize task_sched_runtime()

Rik van Riel (1):
sched/numa: Fix NULL pointer dereference in task_numa_migrate()

kernel/cpu.c | 5 ++++-
kernel/sched/core.c | 14 ++++++++++++++
kernel/sched/fair.c | 31 ++++++++++++++++++++++++++++---
3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 63aa50d..2227b58 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -306,7 +306,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
__func__, cpu);
goto out_release;
}
- smpboot_park_threads(cpu);

/*
* By now we've cleared cpu_active_mask, wait for all preempt-disabled
@@ -315,12 +314,16 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
*
* For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
* not imply sync_sched(), so explicitly call both.
+ *
+ * Do sync before park smpboot threads to take care the rcu boost case.
*/
#ifdef CONFIG_PREEMPT
synchronize_sched();
#endif
synchronize_rcu();

+ smpboot_park_threads(cpu);
+
/*
* So now all preempt/rcu users must observe !cpu_active().
*/
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1deccd7..c180860 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2253,6 +2253,20 @@ unsigned long long task_sched_runtime(struct task_struct *p)
struct rq *rq;
u64 ns = 0;

+#if defined(CONFIG_64BIT) && defined(CONFIG_SMP)
+ /*
+ * 64-bit doesn't need locks to atomically read a 64bit value.
+ * So we have a optimization chance when the task's delta_exec is 0.
+ * Reading ->on_cpu is racy, but this is ok.
+ *
+ * If we race with it leaving cpu, we'll take a lock. So we're correct.
+ * If we race with it entering cpu, unaccounted time is 0. This is
+ * indistinguishable from the read occurring a few cycles earlier.
+ */
+ if (!p->on_cpu)
+ return p->se.sum_exec_runtime;
+#endif
+
rq = task_rq_lock(p, &flags);
ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq);
task_rq_unlock(rq, p, &flags);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index df77c60..e8b652e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1000,7 +1000,7 @@ struct numa_stats {
*/
static void update_numa_stats(struct numa_stats *ns, int nid)
{
- int cpu;
+ int cpu, cpus = 0;

memset(ns, 0, sizeof(*ns));
for_each_cpu(cpu, cpumask_of_node(nid)) {
@@ -1009,8 +1009,21 @@ static void update_numa_stats(struct numa_stats *ns, int nid)
ns->nr_running += rq->nr_running;
ns->load += weighted_cpuload(cpu);
ns->power += power_of(cpu);
+
+ cpus++;
}

+ /*
+ * If we raced with hotplug and there are no CPUs left in our mask
+ * the @ns structure is NULL'ed and task_numa_compare() will
+ * not find this node attractive.
+ *
+ * We'll either bail at !has_capacity, or we'll detect a huge imbalance
+ * and bail there.
+ */
+ if (!cpus)
+ return;
+
ns->load = (ns->load * SCHED_POWER_SCALE) / ns->power;
ns->capacity = DIV_ROUND_CLOSEST(ns->power, SCHED_POWER_SCALE);
ns->has_capacity = (ns->nr_running < ns->capacity);
@@ -1201,9 +1214,21 @@ static int task_numa_migrate(struct task_struct *p)
*/
rcu_read_lock();
sd = rcu_dereference(per_cpu(sd_numa, env.src_cpu));
- env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
+ if (sd)
+ env.imbalance_pct = 100 + (sd->imbalance_pct - 100) / 2;
rcu_read_unlock();

+ /*
+ * Cpusets can break the scheduler domain tree into smaller
+ * balance domains, some of which do not cross NUMA boundaries.
+ * Tasks that are "trapped" in such domains cannot be migrated
+ * elsewhere, so there is no point in (re)trying.
+ */
+ if (unlikely(!sd)) {
+ p->numa_preferred_nid = cpu_to_node(task_cpu(p));
+ return -EINVAL;
+ }
+
taskweight = task_weight(p, env.src_nid);
groupweight = group_weight(p, env.src_nid);
update_numa_stats(&env.src_stats, env.src_nid);
@@ -2153,7 +2178,7 @@ static inline void __update_tg_runnable_avg(struct sched_avg *sa,
long contrib;

/* The fraction of a cpu used by this cfs_rq */
- contrib = div_u64(sa->runnable_avg_sum << NICE_0_SHIFT,
+ contrib = div_u64((u64)sa->runnable_avg_sum << NICE_0_SHIFT,
sa->runnable_avg_period + 1);
contrib -= cfs_rq->tg_runnable_contrib;