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authorLinus Torvalds <torvalds@linux-foundation.org>2021-08-29 10:54:14 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-08-29 10:54:14 -0700
commit537b57bd5a202af145c266d4773971c2c9f90cd9 (patch)
tree62aeacbca0f4cc8a86ae6aa9592c01efc6e23431
parentf20a2637b1b1851cb30fceab68c27aef5fd43a2c (diff)
parente681dcbaa4b284454fecd09617f8b24231448446 (diff)
Merge tag 'sched_urgent_for_v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fixes from Borislav Petkov: - Have get_push_task() check whether current has migration disabled and thus avoid useless invocations of the migration thread - Rework initialization flow so that all rq->core's are initialized, even of CPUs which have not been onlined yet, so that iterating over them all works as expected * tag 'sched_urgent_for_v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched: Fix get_push_task() vs migrate_disable() sched: Fix Core-wide rq->lock for uninitialized CPUs
-rw-r--r--kernel/sched/core.c143
-rw-r--r--kernel/sched/sched.h5
2 files changed, 121 insertions, 27 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 20ffcc044134..f3b27c6c5153 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -237,9 +237,30 @@ static DEFINE_MUTEX(sched_core_mutex);
static atomic_t sched_core_count;
static struct cpumask sched_core_mask;
+static void sched_core_lock(int cpu, unsigned long *flags)
+{
+ const struct cpumask *smt_mask = cpu_smt_mask(cpu);
+ int t, i = 0;
+
+ local_irq_save(*flags);
+ for_each_cpu(t, smt_mask)
+ raw_spin_lock_nested(&cpu_rq(t)->__lock, i++);
+}
+
+static void sched_core_unlock(int cpu, unsigned long *flags)
+{
+ const struct cpumask *smt_mask = cpu_smt_mask(cpu);
+ int t;
+
+ for_each_cpu(t, smt_mask)
+ raw_spin_unlock(&cpu_rq(t)->__lock);
+ local_irq_restore(*flags);
+}
+
static void __sched_core_flip(bool enabled)
{
- int cpu, t, i;
+ unsigned long flags;
+ int cpu, t;
cpus_read_lock();
@@ -250,19 +271,12 @@ static void __sched_core_flip(bool enabled)
for_each_cpu(cpu, &sched_core_mask) {
const struct cpumask *smt_mask = cpu_smt_mask(cpu);
- i = 0;
- local_irq_disable();
- for_each_cpu(t, smt_mask) {
- /* supports up to SMT8 */
- raw_spin_lock_nested(&cpu_rq(t)->__lock, i++);
- }
+ sched_core_lock(cpu, &flags);
for_each_cpu(t, smt_mask)
cpu_rq(t)->core_enabled = enabled;
- for_each_cpu(t, smt_mask)
- raw_spin_unlock(&cpu_rq(t)->__lock);
- local_irq_enable();
+ sched_core_unlock(cpu, &flags);
cpumask_andnot(&sched_core_mask, &sched_core_mask, smt_mask);
}
@@ -5736,35 +5750,109 @@ void queue_core_balance(struct rq *rq)
queue_balance_callback(rq, &per_cpu(core_balance_head, rq->cpu), sched_core_balance);
}
-static inline void sched_core_cpu_starting(unsigned int cpu)
+static void sched_core_cpu_starting(unsigned int cpu)
{
const struct cpumask *smt_mask = cpu_smt_mask(cpu);
- struct rq *rq, *core_rq = NULL;
- int i;
+ struct rq *rq = cpu_rq(cpu), *core_rq = NULL;
+ unsigned long flags;
+ int t;
- core_rq = cpu_rq(cpu)->core;
+ sched_core_lock(cpu, &flags);
- if (!core_rq) {
- for_each_cpu(i, smt_mask) {
- rq = cpu_rq(i);
- if (rq->core && rq->core == rq)
- core_rq = rq;
+ WARN_ON_ONCE(rq->core != rq);
+
+ /* if we're the first, we'll be our own leader */
+ if (cpumask_weight(smt_mask) == 1)
+ goto unlock;
+
+ /* find the leader */
+ for_each_cpu(t, smt_mask) {
+ if (t == cpu)
+ continue;
+ rq = cpu_rq(t);
+ if (rq->core == rq) {
+ core_rq = rq;
+ break;
}
+ }
- if (!core_rq)
- core_rq = cpu_rq(cpu);
+ if (WARN_ON_ONCE(!core_rq)) /* whoopsie */
+ goto unlock;
- for_each_cpu(i, smt_mask) {
- rq = cpu_rq(i);
+ /* install and validate core_rq */
+ for_each_cpu(t, smt_mask) {
+ rq = cpu_rq(t);
- WARN_ON_ONCE(rq->core && rq->core != core_rq);
+ if (t == cpu)
rq->core = core_rq;
- }
+
+ WARN_ON_ONCE(rq->core != core_rq);
}
+
+unlock:
+ sched_core_unlock(cpu, &flags);
}
+
+static void sched_core_cpu_deactivate(unsigned int cpu)
+{
+ const struct cpumask *smt_mask = cpu_smt_mask(cpu);
+ struct rq *rq = cpu_rq(cpu), *core_rq = NULL;
+ unsigned long flags;
+ int t;
+
+ sched_core_lock(cpu, &flags);
+
+ /* if we're the last man standing, nothing to do */
+ if (cpumask_weight(smt_mask) == 1) {
+ WARN_ON_ONCE(rq->core != rq);
+ goto unlock;
+ }
+
+ /* if we're not the leader, nothing to do */
+ if (rq->core != rq)
+ goto unlock;
+
+ /* find a new leader */
+ for_each_cpu(t, smt_mask) {
+ if (t == cpu)
+ continue;
+ core_rq = cpu_rq(t);
+ break;
+ }
+
+ if (WARN_ON_ONCE(!core_rq)) /* impossible */
+ goto unlock;
+
+ /* copy the shared state to the new leader */
+ core_rq->core_task_seq = rq->core_task_seq;
+ core_rq->core_pick_seq = rq->core_pick_seq;
+ core_rq->core_cookie = rq->core_cookie;
+ core_rq->core_forceidle = rq->core_forceidle;
+ core_rq->core_forceidle_seq = rq->core_forceidle_seq;
+
+ /* install new leader */
+ for_each_cpu(t, smt_mask) {
+ rq = cpu_rq(t);
+ rq->core = core_rq;
+ }
+
+unlock:
+ sched_core_unlock(cpu, &flags);
+}
+
+static inline void sched_core_cpu_dying(unsigned int cpu)
+{
+ struct rq *rq = cpu_rq(cpu);
+
+ if (rq->core != rq)
+ rq->core = rq;
+}
+
#else /* !CONFIG_SCHED_CORE */
static inline void sched_core_cpu_starting(unsigned int cpu) {}
+static inline void sched_core_cpu_deactivate(unsigned int cpu) {}
+static inline void sched_core_cpu_dying(unsigned int cpu) {}
static struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
@@ -8707,6 +8795,8 @@ int sched_cpu_deactivate(unsigned int cpu)
*/
if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
static_branch_dec_cpuslocked(&sched_smt_present);
+
+ sched_core_cpu_deactivate(cpu);
#endif
if (!sched_smp_initialized)
@@ -8811,6 +8901,7 @@ int sched_cpu_dying(unsigned int cpu)
calc_load_migrate(rq);
update_max_interval();
hrtick_clear(rq);
+ sched_core_cpu_dying(cpu);
return 0;
}
#endif
@@ -9022,7 +9113,7 @@ void __init sched_init(void)
atomic_set(&rq->nr_iowait, 0);
#ifdef CONFIG_SCHED_CORE
- rq->core = NULL;
+ rq->core = rq;
rq->core_pick = NULL;
rq->core_enabled = 0;
rq->core_tree = RB_ROOT;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 14a41a243f7b..ddefb0419d7a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1093,7 +1093,7 @@ struct rq {
unsigned int core_sched_seq;
struct rb_root core_tree;
- /* shared state */
+ /* shared state -- careful with sched_core_cpu_deactivate() */
unsigned int core_task_seq;
unsigned int core_pick_seq;
unsigned long core_cookie;
@@ -2255,6 +2255,9 @@ static inline struct task_struct *get_push_task(struct rq *rq)
if (p->nr_cpus_allowed == 1)
return NULL;
+ if (p->migration_disabled)
+ return NULL;
+
rq->push_busy = true;
return get_task_struct(p);
}

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