[GIT PULL] scheduler fixes

Ingo Molnar
2011-06-07T18:01:50Z

Linus,

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

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git sched-urgent-for-linus

Thanks,

Ingo

------------------>
Peter Zijlstra (4):
sched: Fix cross-cpu clock sync on remote wakeups
sched: Fix schedstat.nr_wakeups_migrate
lockdep: Fix lock_is_held() on recursion
sched: Fix/clarify set_task_cpu() locking rules

include/linux/sched.h | 1 +
kernel/lockdep.c | 2 +-
kernel/sched.c | 33 ++++++++++++++++++++++++---------
3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8da84b7..483c1ed 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1063,6 +1063,7 @@ struct sched_domain;
*/
#define WF_SYNC 0x01 /* waker goes to sleep after wakup */
#define WF_FORK 0x02 /* child wakeup after fork */
+#define WF_MIGRATED 0x04 /* internal use, task got migrated */

#define ENQUEUE_WAKEUP 1
#define ENQUEUE_HEAD 2
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 63437d0..298c927 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -3426,7 +3426,7 @@ int lock_is_held(struct lockdep_map *lock)
int ret = 0;

if (unlikely(current->lockdep_recursion))
- return ret;
+ return 1; /* avoid false negative lockdep_assert_held() */

raw_local_irq_save(flags);
check_flags(flags);
diff --git a/kernel/sched.c b/kernel/sched.c
index cbb3a0e..3f2e502 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -605,10 +605,10 @@ static inline int cpu_of(struct rq *rq)
/*
* Return the group to which this tasks belongs.
*
- * We use task_subsys_state_check() and extend the RCU verification
- * with lockdep_is_held(&p->pi_lock) because cpu_cgroup_attach()
- * holds that lock for each task it moves into the cgroup. Therefore
- * by holding that lock, we pin the task to the current cgroup.
+ * We use task_subsys_state_check() and extend the RCU verification with
+ * pi->lock and rq->lock because cpu_cgroup_attach() holds those locks for each
+ * task it moves into the cgroup. Therefore by holding either of those locks,
+ * we pin the task to the current cgroup.
*/
static inline struct task_group *task_group(struct task_struct *p)
{
@@ -616,7 +616,8 @@ static inline struct task_group *task_group(struct task_struct *p)
struct cgroup_subsys_state *css;

css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
- lockdep_is_held(&p->pi_lock));
+ lockdep_is_held(&p->pi_lock) ||
+ lockdep_is_held(&task_rq(p)->lock));
tg = container_of(css, struct task_group, css);

return autogroup_task_group(p, tg);
@@ -2200,6 +2201,16 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
!(task_thread_info(p)->preempt_count & PREEMPT_ACTIVE));

#ifdef CONFIG_LOCKDEP
+ /*
+ * The caller should hold either p->pi_lock or rq->lock, when changing
+ * a task's CPU. ->pi_lock for waking tasks, rq->lock for runnable tasks.
+ *
+ * sched_move_task() holds both and thus holding either pins the cgroup,
+ * see set_task_rq().
+ *
+ * Furthermore, all task_rq users should acquire both locks, see
+ * task_rq_lock().
+ */
WARN_ON_ONCE(debug_locks && !(lockdep_is_held(&p->pi_lock) ||
lockdep_is_held(&task_rq(p)->lock)));
#endif
@@ -2447,6 +2458,10 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
}
rcu_read_unlock();
}
+
+ if (wake_flags & WF_MIGRATED)
+ schedstat_inc(p, se.statistics.nr_wakeups_migrate);
+
#endif /* CONFIG_SMP */

schedstat_inc(rq, ttwu_count);
@@ -2455,9 +2470,6 @@ ttwu_stat(struct task_struct *p, int cpu, int wake_flags)
if (wake_flags & WF_SYNC)
schedstat_inc(p, se.statistics.nr_wakeups_sync);

- if (cpu != task_cpu(p))
- schedstat_inc(p, se.statistics.nr_wakeups_migrate);
-
#endif /* CONFIG_SCHEDSTATS */
}

@@ -2600,6 +2612,7 @@ static void ttwu_queue(struct task_struct *p, int cpu)

#if defined(CONFIG_SMP)
if (sched_feat(TTWU_QUEUE) && cpu != smp_processor_id()) {
+ sched_clock_cpu(cpu); /* sync clocks x-cpu */
ttwu_queue_remote(p, cpu);
return;
}
@@ -2674,8 +2687,10 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
p->sched_class->task_waking(p);

cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
- if (task_cpu(p) != cpu)
+ if (task_cpu(p) != cpu) {
+ wake_flags |= WF_MIGRATED;
set_task_cpu(p, cpu);
+ }
#endif /* CONFIG_SMP */

ttwu_queue(p, cpu);