commit 56ea74ecece682052425b86bae3cebf025f36855
author Pavankumar Kondeti <pkondeti@codeaurora.org> Mon Nov 28 20:55:58 2016 +0530
committer Syed Rameez Mustafa <rameezmustafa@codeaurora.org> Tue Feb 07 14:51:23 2017 -0800
tree 670ee194a8b466b2f9499c8878f6eda7f1f3fae8
parent 1e8a44cc8fadac3eeeee062f2a26e878e73c7590

sched: Disable interrupts while holding related_thread_group_lock

There is a potential deadlock condition if interrupts are enabled
while holding the related_thread_group_lock. Prevent this.

----------------                              --------------------
    CPU 0                                          CPU 1
---------------                               --------------------

check_for_migration()                         cgroup_file_write(p)

check_for_freq_change()                       cgroup_attach_task(p)

send_notification()                           schedtune_attach(p)

read_lock(&related_thread_group_lock)         sched_set_group_id(p)

                                              raw_spin_lock_irqsave(
					       &p->pi_lock, flags)

					      write_lock_irqsave(
					       &related_thread_group_lock)

					       waiting on CPU#0

raw_spin_lock_irqsave(&rq->lock, flags)

raw_spin_unlock_irqrestore(&rq->lock, flags)

--> interrupt()

----> ttwu(p)

-------> waiting for p's pi_lock on CPU#1

Change-Id: I6f0f8f742d6e1b3ff735dcbeabd54ef101329cdf
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>

kernel/sched/hmp.c

diff --git a/kernel/sched/hmp.c b/kernel/sched/hmp.c
index 127cb00..11c97e7 100644
--- a/kernel/sched/hmp.c
+++ b/kernel/sched/hmp.c
@@ -1745,20 +1745,20 @@ static int send_notification(struct rq *rq, int check_pred, int check_groups)
 		if (freq_required < cur_freq + sysctl_sched_pred_alert_freq)
 			return 0;
 	} else {
-		read_lock(&related_thread_group_lock);
+		read_lock_irqsave(&related_thread_group_lock, flags);
 		/*
 		 * Protect from concurrent update of rq->prev_runnable_sum and
 		 * group cpu load
 		 */
-		raw_spin_lock_irqsave(&rq->lock, flags);
+		raw_spin_lock(&rq->lock);
 		if (check_groups)
 			_group_load_in_cpu(cpu_of(rq), &group_load, NULL);
 
 		new_load = rq->prev_runnable_sum + group_load;
 		new_load = freq_policy_load(rq, new_load);
 
-		raw_spin_unlock_irqrestore(&rq->lock, flags);
-		read_unlock(&related_thread_group_lock);
+		raw_spin_unlock(&rq->lock);
+		read_unlock_irqrestore(&related_thread_group_lock, flags);
 
 		cur_freq = load_to_freq(rq, rq->old_busy_time);
 		freq_required = load_to_freq(rq, new_load);
@@ -3180,14 +3180,16 @@ void sched_get_cpus_busy(struct sched_load *busy,
 	if (unlikely(cpus == 0))
 		return;
 
+	local_irq_save(flags);
+
+	read_lock(&related_thread_group_lock);
+
 	/*
 	 * This function could be called in timer context, and the
 	 * current task may have been executing for a long time. Ensure
 	 * that the window stats are current by doing an update.
 	 */
-	read_lock(&related_thread_group_lock);
 
-	local_irq_save(flags);
 	for_each_cpu(cpu, query_cpus)
 		raw_spin_lock(&cpu_rq(cpu)->lock);
 
@@ -3287,10 +3289,11 @@ void sched_get_cpus_busy(struct sched_load *busy,
 
 	for_each_cpu(cpu, query_cpus)
 		raw_spin_unlock(&(cpu_rq(cpu))->lock);
-	local_irq_restore(flags);
 
 	read_unlock(&related_thread_group_lock);
 
+	local_irq_restore(flags);
+
 	i = 0;
 	for_each_cpu(cpu, query_cpus) {
 		rq = cpu_rq(cpu);