From: Peter Zijlstra <peterz@infradead.org>
To: tglx@linutronix.de, mingo@kernel.org
Cc: linux-kernel@vger.kernel.org, bigeasy@linutronix.de,
qais.yousef@arm.com, swood@redhat.com, peterz@infradead.org,
valentin.schneider@arm.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
bristot@redhat.com, vincent.donnefort@arm.com, tj@kernel.org,
ouwen210@hotmail.com
Subject: [PATCH v4 02/19] sched: Fix balance_callback()
Date: Fri, 23 Oct 2020 12:12:00 +0200 [thread overview]
Message-ID: <20201023102346.203901269@infradead.org> (raw)
In-Reply-To: 20201023101158.088940906@infradead.org
The intent of balance_callback() has always been to delay executing
balancing operations until the end of the current rq->lock section.
This is because balance operations must often drop rq->lock, and that
isn't safe in general.
However, as noted by Scott, there were a few holes in that scheme;
balance_callback() was called after rq->lock was dropped, which means
another CPU can interleave and touch the callback list.
Rework code to call the balance callbacks before dropping rq->lock
where possible, and otherwise splice the balance list onto a local
stack.
This guarantees that the balance list must be empty when we take
rq->lock. IOW, we'll only ever run our own balance callbacks.
Reported-by: Scott Wood <swood@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/core.c | 119 ++++++++++++++++++++++++++++++++-------------------
kernel/sched/sched.h | 3 +
2 files changed, 78 insertions(+), 44 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3494,6 +3494,69 @@ static inline void finish_task(struct ta
#endif
}
+#ifdef CONFIG_SMP
+
+static void do_balance_callbacks(struct rq *rq, struct callback_head *head)
+{
+ void (*func)(struct rq *rq);
+ struct callback_head *next;
+
+ lockdep_assert_held(&rq->lock);
+
+ while (head) {
+ func = (void (*)(struct rq *))head->func;
+ next = head->next;
+ head->next = NULL;
+ head = next;
+
+ func(rq);
+ }
+}
+
+static inline struct callback_head *splice_balance_callbacks(struct rq *rq)
+{
+ struct callback_head *head = rq->balance_callback;
+
+ lockdep_assert_held(&rq->lock);
+ if (head)
+ rq->balance_callback = NULL;
+
+ return head;
+}
+
+static void __balance_callbacks(struct rq *rq)
+{
+ do_balance_callbacks(rq, splice_balance_callbacks(rq));
+}
+
+static inline void balance_callbacks(struct rq *rq, struct callback_head *head)
+{
+ unsigned long flags;
+
+ if (unlikely(head)) {
+ raw_spin_lock_irqsave(&rq->lock, flags);
+ do_balance_callbacks(rq, head);
+ raw_spin_unlock_irqrestore(&rq->lock, flags);
+ }
+}
+
+#else
+
+static inline void __balance_callbacks(struct rq *rq)
+{
+}
+
+static inline struct callback_head *splice_balance_callbacks(struct rq *rq)
+{
+ return NULL;
+}
+
+static inline void balance_callbacks(struct rq *rq, struct callback_head *head)
+{
+}
+
+#endif
+
static inline void
prepare_lock_switch(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
{
@@ -3519,6 +3582,7 @@ static inline void finish_lock_switch(st
* prev into current:
*/
spin_acquire(&rq->lock.dep_map, 0, 0, _THIS_IP_);
+ __balance_callbacks(rq);
raw_spin_unlock_irq(&rq->lock);
}
@@ -3660,43 +3724,6 @@ static struct rq *finish_task_switch(str
return rq;
}
-#ifdef CONFIG_SMP
-
-/* rq->lock is NOT held, but preemption is disabled */
-static void __balance_callback(struct rq *rq)
-{
- struct callback_head *head, *next;
- void (*func)(struct rq *rq);
- unsigned long flags;
-
- raw_spin_lock_irqsave(&rq->lock, flags);
- head = rq->balance_callback;
- rq->balance_callback = NULL;
- while (head) {
- func = (void (*)(struct rq *))head->func;
- next = head->next;
- head->next = NULL;
- head = next;
-
- func(rq);
- }
- raw_spin_unlock_irqrestore(&rq->lock, flags);
-}
-
-static inline void balance_callback(struct rq *rq)
-{
- if (unlikely(rq->balance_callback))
- __balance_callback(rq);
-}
-
-#else
-
-static inline void balance_callback(struct rq *rq)
-{
-}
-
-#endif
-
/**
* schedule_tail - first thing a freshly forked thread must call.
* @prev: the thread we just switched away from.
@@ -3716,7 +3743,6 @@ asmlinkage __visible void schedule_tail(
*/
rq = finish_task_switch(prev);
- balance_callback(rq);
preempt_enable();
if (current->set_child_tid)
@@ -4532,10 +4558,11 @@ static void __sched notrace __schedule(b
rq = context_switch(rq, prev, next, &rf);
} else {
rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
- rq_unlock_irq(rq, &rf);
- }
- balance_callback(rq);
+ rq_unpin_lock(rq, &rf);
+ __balance_callbacks(rq);
+ raw_spin_unlock_irq(&rq->lock);
+ }
}
void __noreturn do_task_dead(void)
@@ -4946,9 +4973,11 @@ void rt_mutex_setprio(struct task_struct
out_unlock:
/* Avoid rq from going away on us: */
preempt_disable();
- __task_rq_unlock(rq, &rf);
- balance_callback(rq);
+ rq_unpin_lock(rq, &rf);
+ __balance_callbacks(rq);
+ raw_spin_unlock(&rq->lock);
+
preempt_enable();
}
#else
@@ -5222,6 +5251,7 @@ static int __sched_setscheduler(struct t
int retval, oldprio, oldpolicy = -1, queued, running;
int new_effective_prio, policy = attr->sched_policy;
const struct sched_class *prev_class;
+ struct callback_head *head;
struct rq_flags rf;
int reset_on_fork;
int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
@@ -5460,6 +5490,7 @@ static int __sched_setscheduler(struct t
/* Avoid rq from going away on us: */
preempt_disable();
+ head = splice_balance_callbacks(rq);
task_rq_unlock(rq, p, &rf);
if (pi) {
@@ -5468,7 +5499,7 @@ static int __sched_setscheduler(struct t
}
/* Run balance callbacks after we've adjusted the PI chain: */
- balance_callback(rq);
+ balance_callbacks(rq, head);
preempt_enable();
return 0;
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1221,6 +1221,9 @@ static inline void rq_pin_lock(struct rq
rq->clock_update_flags &= (RQCF_REQ_SKIP|RQCF_ACT_SKIP);
rf->clock_update_flags = 0;
#endif
+#ifdef CONFIG_SMP
+ SCHED_WARN_ON(rq->balance_callback);
+#endif
}
static inline void rq_unpin_lock(struct rq *rq, struct rq_flags *rf)
next prev parent reply other threads:[~2020-10-23 10:26 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-23 10:11 [PATCH v4 00/19] sched: Migrate disable support Peter Zijlstra
2020-10-23 10:11 ` [PATCH v4 01/19] stop_machine: Add function and caller debug info Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` Peter Zijlstra [this message]
2020-11-11 8:23 ` [tip: sched/core] sched: Fix balance_callback() tip-bot2 for Peter Zijlstra
2020-11-11 20:30 ` Paul Bolle
2020-11-11 20:45 ` Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 03/19] sched/hotplug: Ensure only per-cpu kthreads run during hotplug Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 04/19] sched/core: Wait for tasks being pushed away on hotplug Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Thomas Gleixner
2020-10-23 10:12 ` [PATCH v4 05/19] workqueue: Manually break affinity " Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 06/19] sched/hotplug: Consolidate task migration on CPU unplug Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Thomas Gleixner
2020-10-23 10:12 ` [PATCH v4 07/19] sched: Fix hotplug vs CPU bandwidth control Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 08/19] sched: Massage set_cpus_allowed() Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 09/19] sched: Add migrate_disable() Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 10/19] sched: Fix migrate_disable() vs set_cpus_allowed_ptr() Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-11-12 16:38 ` [PATCH v4 10/19] " Qian Cai
2020-11-12 17:26 ` Valentin Schneider
2020-11-12 18:01 ` Qian Cai
2020-11-12 19:31 ` Valentin Schneider
2020-11-12 19:41 ` Qian Cai
2020-11-12 20:37 ` Qian Cai
2020-11-12 21:26 ` Valentin Schneider
2020-11-13 10:27 ` Peter Zijlstra
2020-11-12 18:35 ` Qian Cai
2020-11-20 12:34 ` [tip: sched/core] sched/core: Add missing completion for affine_move_task() waiters tip-bot2 for Valentin Schneider
2020-10-23 10:12 ` [PATCH v4 11/19] sched/core: Make migrate disable and CPU hotplug cooperative Peter Zijlstra
2020-10-29 16:27 ` Valentin Schneider
2020-10-29 17:34 ` Peter Zijlstra
2020-10-29 17:55 ` Valentin Schneider
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Thomas Gleixner
2020-11-13 15:06 ` [PATCH v4 11/19] " Qian Cai
2020-11-17 19:28 ` Valentin Schneider
2020-11-18 14:44 ` Qian Cai
2020-11-23 18:13 ` Sebastian Andrzej Siewior
2020-12-02 21:59 ` Qian Cai
2020-12-03 12:31 ` Qian Cai
2020-12-04 0:23 ` Qian Cai
2020-12-04 21:19 ` Qian Cai
2020-12-05 18:37 ` Valentin Schneider
2020-12-06 1:17 ` Qian Cai
2020-12-07 19:27 ` Valentin Schneider
2020-12-08 13:46 ` Qian Cai
2020-12-09 19:16 ` Valentin Schneider
2020-10-23 10:12 ` [PATCH v4 12/19] sched,rt: Use cpumask_any*_distribute() Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 13/19] sched,rt: Use the full cpumask for balancing Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 14/19] sched, lockdep: Annotate ->pi_lock recursion Peter Zijlstra
2020-10-29 16:27 ` Valentin Schneider
2020-10-29 17:38 ` Peter Zijlstra
2020-10-29 18:09 ` Valentin Schneider
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 15/19] sched: Fix migrate_disable() vs rt/dl balancing Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-12-26 13:54 ` [PATCH v4 15/19] " Qais Yousef
2021-03-05 14:56 ` Peter Zijlstra
2021-03-05 15:41 ` Valentin Schneider
2021-03-05 17:11 ` Qais Yousef
2021-03-10 14:44 ` Qais Yousef
2021-03-05 16:48 ` Qais Yousef
2020-10-23 10:12 ` [PATCH v4 16/19] sched/proc: Print accurate cpumask vs migrate_disable() Peter Zijlstra
2020-11-11 8:23 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 17/19] sched: Add migrate_disable() tracepoints Peter Zijlstra
2020-10-29 16:27 ` Valentin Schneider
2020-10-29 17:43 ` Peter Zijlstra
2020-10-29 17:56 ` Valentin Schneider
2020-10-29 17:59 ` Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 18/19] sched: Deny self-issued __set_cpus_allowed_ptr() when migrate_disable() Peter Zijlstra
2020-10-23 10:12 ` [PATCH v4 19/19] sched: Comment affine_move_task() Peter Zijlstra
2020-10-29 16:27 ` Valentin Schneider
2020-10-29 17:44 ` Peter Zijlstra
2020-10-29 19:03 ` [PATCH v4 00/19] sched: Migrate disable support Valentin Schneider
2020-11-09 16:39 ` Daniel Bristot de Oliveira
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