[tip:sched/hrtimers] sched,lockdep: Employ lock pinning

From: tip-bot for Peter Zijlstra
Date: Thu Jun 18 2015 - 19:04:46 EST

Commit-ID: cbce1a686700595de65ee363b9b3283ae85d8fc5
Gitweb: http://git.kernel.org/tip/cbce1a686700595de65ee363b9b3283ae85d8fc5
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 11 Jun 2015 14:46:54 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 19 Jun 2015 00:25:27 +0200

sched,lockdep: Employ lock pinning

Employ the new lockdep lock pinning annotation to ensure no
'accidental' lock-breaks happen with rq->lock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: ktkhai@xxxxxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: juri.lelli@xxxxxxxxx
Cc: pang.xunlei@xxxxxxxxxx
Cc: oleg@xxxxxxxxxx
Cc: wanpeng.li@xxxxxxxxxxxxxxx
Cc: umgwanakikbuti@xxxxxxxxx
Link: http://lkml.kernel.org/r/20150611124744.003233193@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/sched/core.c | 42 +++++++++++++++++++++++++++++++++++++++---
kernel/sched/deadline.c | 8 ++++++++
kernel/sched/fair.c | 11 ++++++++---
kernel/sched/rt.c | 8 ++++++++
kernel/sched/sched.h | 10 ++++++++--
5 files changed, 71 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1ddc129..c74191a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1201,8 +1201,15 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
tlb_migrate_finish(p->mm);
return 0;
- } else if (task_on_rq_queued(p))
+ } else if (task_on_rq_queued(p)) {
+ /*
+ * OK, since we're going to drop the lock immediately
+ * afterwards anyway.
+ */
+ lockdep_unpin_lock(&rq->lock);
rq = move_queued_task(rq, p, dest_cpu);
+ lockdep_pin_lock(&rq->lock);
+ }
out:
task_rq_unlock(rq, p, &flags);

@@ -1562,6 +1569,8 @@ out:
static inline
int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags)
{
+ lockdep_assert_held(&p->pi_lock);
+
if (p->nr_cpus_allowed > 1)
cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags);

@@ -1652,9 +1661,12 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
#ifdef CONFIG_SMP
if (p->sched_class->task_woken) {
/*
- * XXX can drop rq->lock; most likely ok.
+ * Our task @p is fully woken up and running; so its safe to
+ * drop the rq->lock, hereafter rq is only used for statistics.
*/
+ lockdep_unpin_lock(&rq->lock);
p->sched_class->task_woken(rq, p);
+ lockdep_pin_lock(&rq->lock);
}

if (rq->idle_stamp) {
@@ -1674,6 +1686,8 @@ ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags)
static void
ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags)
{
+ lockdep_assert_held(&rq->lock);
+
#ifdef CONFIG_SMP
if (p->sched_contributes_to_load)
rq->nr_uninterruptible--;
@@ -1718,6 +1732,7 @@ void sched_ttwu_pending(void)
return;

raw_spin_lock_irqsave(&rq->lock, flags);
+ lockdep_pin_lock(&rq->lock);

while (llist) {
p = llist_entry(llist, struct task_struct, wake_entry);
@@ -1725,6 +1740,7 @@ void sched_ttwu_pending(void)
ttwu_do_activate(rq, p, 0);
}

+ lockdep_unpin_lock(&rq->lock);
raw_spin_unlock_irqrestore(&rq->lock, flags);
}

@@ -1821,7 +1837,9 @@ static void ttwu_queue(struct task_struct *p, int cpu)
#endif

raw_spin_lock(&rq->lock);
+ lockdep_pin_lock(&rq->lock);
ttwu_do_activate(rq, p, 0);
+ lockdep_unpin_lock(&rq->lock);
raw_spin_unlock(&rq->lock);
}

@@ -1916,9 +1934,17 @@ static void try_to_wake_up_local(struct task_struct *p)
lockdep_assert_held(&rq->lock);

if (!raw_spin_trylock(&p->pi_lock)) {
+ /*
+ * This is OK, because current is on_cpu, which avoids it being
+ * picked for load-balance and preemption/IRQs are still
+ * disabled avoiding further scheduler activity on it and we've
+ * not yet picked a replacement task.
+ */
+ lockdep_unpin_lock(&rq->lock);
raw_spin_unlock(&rq->lock);
raw_spin_lock(&p->pi_lock);
raw_spin_lock(&rq->lock);
+ lockdep_pin_lock(&rq->lock);
}

if (!(p->state & TASK_NORMAL))
@@ -2530,6 +2556,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
* of the scheduler it's an obvious special-case), so we
* do an early lockdep release here:
*/
+ lockdep_unpin_lock(&rq->lock);
spin_release(&rq->lock.dep_map, 1, _THIS_IP_);

context_tracking_task_switch(prev, next);
@@ -2953,6 +2980,7 @@ static void __sched __schedule(void)
*/
smp_mb__before_spinlock();
raw_spin_lock_irq(&rq->lock);
+ lockdep_pin_lock(&rq->lock);

rq->clock_skip_update <<= 1; /* promote REQ to ACT */

@@ -2995,8 +3023,10 @@ static void __sched __schedule(void)

rq = context_switch(rq, prev, next); /* unlocks the rq */
cpu = cpu_of(rq);
- } else
+ } else {
+ lockdep_unpin_lock(&rq->lock);
raw_spin_unlock_irq(&rq->lock);
+ }

balance_callback(rq);
}
@@ -5065,6 +5095,11 @@ static void migrate_tasks(struct rq *dead_rq)
if (rq->nr_running == 1)
break;

+ /*
+ * Ensure rq->lock covers the entire task selection
+ * until the migration.
+ */
+ lockdep_pin_lock(&rq->lock);
next = pick_next_task(rq, &fake_task);
BUG_ON(!next);
next->sched_class->put_prev_task(rq, next);
@@ -5072,6 +5107,7 @@ static void migrate_tasks(struct rq *dead_rq)
/* Find suitable destination for @next, with force if needed. */
dest_cpu = select_fallback_rq(dead_rq->cpu, next);

+ lockdep_unpin_lock(&rq->lock);
rq = __migrate_task(rq, next, dest_cpu);
if (rq != dead_rq) {
raw_spin_unlock(&rq->lock);
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 6318f43..e814641 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1151,7 +1151,15 @@ struct task_struct *pick_next_task_dl(struct rq *rq, struct task_struct *prev)
dl_rq = &rq->dl;

if (need_pull_dl_task(rq, prev)) {
+ /*
+ * This is OK, because current is on_cpu, which avoids it being
+ * picked for load-balance and preemption/IRQs are still
+ * disabled avoiding further scheduler activity on it and we're
+ * being very careful to re-start the picking loop.
+ */
+ lockdep_unpin_lock(&rq->lock);
pull_dl_task(rq);
+ lockdep_pin_lock(&rq->lock);
/*
* pull_rt_task() can drop (and re-acquire) rq->lock; this
* means a stop task can slip in, in which case we need to
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7210ae8..509ef63 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5392,7 +5392,15 @@ simple:
return p;

idle:
+ /*
+ * This is OK, because current is on_cpu, which avoids it being picked
+ * for load-balance and preemption/IRQs are still disabled avoiding
+ * further scheduler activity on it and we're being very careful to
+ * re-start the picking loop.
+ */
+ lockdep_unpin_lock(&rq->lock);
new_tasks = idle_balance(rq);
+ lockdep_pin_lock(&rq->lock);
/*
* Because idle_balance() releases (and re-acquires) rq->lock, it is
* possible for any higher priority task to appear. In that case we
@@ -7426,9 +7434,6 @@ static int idle_balance(struct rq *this_rq)
goto out;
}

- /*
- * Drop the rq->lock, but keep IRQ/preempt disabled.
- */
raw_spin_unlock(&this_rq->lock);

update_blocked_averages(this_cpu);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 460f858..0d193a24 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1478,7 +1478,15 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev)
struct rt_rq *rt_rq = &rq->rt;

if (need_pull_rt_task(rq, prev)) {
+ /*
+ * This is OK, because current is on_cpu, which avoids it being
+ * picked for load-balance and preemption/IRQs are still
+ * disabled avoiding further scheduler activity on it and we're
+ * being very careful to re-start the picking loop.
+ */
+ lockdep_unpin_lock(&rq->lock);
pull_rt_task(rq);
+ lockdep_pin_lock(&rq->lock);
/*
* pull_rt_task() can drop (and re-acquire) rq->lock; this
* means a dl or stop task can slip in, in which case we need
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 62949ab..ef02d11 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1439,8 +1439,10 @@ static inline struct rq *__task_rq_lock(struct task_struct *p)
for (;;) {
rq = task_rq(p);
raw_spin_lock(&rq->lock);
- if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+ if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
+ lockdep_pin_lock(&rq->lock);
return rq;
+ }
raw_spin_unlock(&rq->lock);

while (unlikely(task_on_rq_migrating(p)))
@@ -1477,8 +1479,10 @@ static inline struct rq *task_rq_lock(struct task_struct *p, unsigned long *flag
* If we observe the new cpu in task_rq_lock, the acquire will
* pair with the WMB to ensure we must then also see migrating.
*/
- if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+ if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
+ lockdep_pin_lock(&rq->lock);
return rq;
+ }
raw_spin_unlock(&rq->lock);
raw_spin_unlock_irqrestore(&p->pi_lock, *flags);

@@ -1490,6 +1494,7 @@ static inline struct rq *task_rq_lock(struct task_struct *p, unsigned long *flag
static inline void __task_rq_unlock(struct rq *rq)
__releases(rq->lock)
{
+ lockdep_unpin_lock(&rq->lock);
raw_spin_unlock(&rq->lock);
}

@@ -1498,6 +1503,7 @@ task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags)
__releases(rq->lock)
__releases(p->pi_lock)
{
+ lockdep_unpin_lock(&rq->lock);
raw_spin_unlock(&rq->lock);
raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
}
--
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