sched: group scheduling, minor fixes

Minor bug fixes for the group scheduler:

- Use a mutex to serialize add/remove of task groups and also when
  changing shares of a task group. Use the same mutex when printing
  cfs_rq debugging stats for various task groups.

- Use list_for_each_entry_rcu in for_each_leaf_cfs_rq macro (when
  walking task group list)

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 28 insertions, 9 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 7f827b70ae02..cfa695819252 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -169,8 +169,6 @@ struct task_group {
         /* runqueue "owned" by this group on each cpu */
         struct cfs_rq **cfs_rq;
         unsigned long shares;
-        /* spinlock to serialize modification to shares */
-        spinlock_t lock;
         struct rcu_head rcu;
 };
 
@@ -182,6 +180,11 @@ static DEFINE_PER_CPU(struct cfs_rq, init_cfs_rq) ____cacheline_aligned_in_smp;
 static struct sched_entity *init_sched_entity_p[NR_CPUS];
 static struct cfs_rq *init_cfs_rq_p[NR_CPUS];
 
+/* task_group_mutex serializes add/remove of task groups and also changes to
+ * a task group's cpu shares.
+ */
+static DEFINE_MUTEX(task_group_mutex);
+
 /* Default task group.
  *      Every task in system belong to this group at bootup.
  */
@@ -221,9 +224,21 @@ static inline void set_task_cfs_rq(struct task_struct *p, unsigned int cpu)
         p->se.parent = task_group(p)->se[cpu];
 }
 
+static inline void lock_task_group_list(void)
+{
+        mutex_lock(&task_group_mutex);
+}
+
+static inline void unlock_task_group_list(void)
+{
+        mutex_unlock(&task_group_mutex);
+}
+
 #else
 
 static inline void set_task_cfs_rq(struct task_struct *p, unsigned int cpu) { }
+static inline void lock_task_group_list(void) { }
+static inline void unlock_task_group_list(void) { }
 
 #endif  /* CONFIG_FAIR_GROUP_SCHED */
 
@@ -6768,7 +6783,6 @@ void __init sched_init(void)
                         se->parent = NULL;
                 }
                 init_task_group.shares = init_task_group_load;
-                spin_lock_init(&init_task_group.lock);
 #endif
 
                 for (j = 0; j < CPU_LOAD_IDX_MAX; j++)
@@ -7008,14 +7022,15 @@ struct task_group *sched_create_group(void)
                 se->parent = NULL;
         }
 
+        tg->shares = NICE_0_LOAD;
+
+        lock_task_group_list();
         for_each_possible_cpu(i) {
                 rq = cpu_rq(i);
                 cfs_rq = tg->cfs_rq[i];
                 list_add_rcu(&cfs_rq->leaf_cfs_rq_list, &rq->leaf_cfs_rq_list);
         }
-
-        tg->shares = NICE_0_LOAD;
-        spin_lock_init(&tg->lock);
+        unlock_task_group_list();
 
         return tg;
 
@@ -7061,10 +7076,12 @@ void sched_destroy_group(struct task_group *tg)
         struct cfs_rq *cfs_rq = NULL;
         int i;
 
+        lock_task_group_list();
         for_each_possible_cpu(i) {
                 cfs_rq = tg->cfs_rq[i];
                 list_del_rcu(&cfs_rq->leaf_cfs_rq_list);
         }
+        unlock_task_group_list();
 
         BUG_ON(!cfs_rq);
 
@@ -7146,7 +7163,7 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)
         if (shares < 2)
                 shares = 2;
 
-        spin_lock(&tg->lock);
+        lock_task_group_list();
         if (tg->shares == shares)
                 goto done;
 
@@ -7155,7 +7172,7 @@ int sched_group_set_shares(struct task_group *tg, unsigned long shares)
                 set_se_shares(tg->se[i], shares);
 
 done:
-        spin_unlock(&tg->lock);
+        unlock_task_group_list();
         return 0;
 }
 
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index da7c061e7206..0c5fdce67228 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -690,7 +690,7 @@ static inline struct cfs_rq *cpu_cfs_rq(struct cfs_rq *cfs_rq, int this_cpu)
 
 /* Iterate thr' all leaf cfs_rq's on a runqueue */
 #define for_each_leaf_cfs_rq(rq, cfs_rq) \
-        list_for_each_entry(cfs_rq, &rq->leaf_cfs_rq_list, leaf_cfs_rq_list)
+        list_for_each_entry_rcu(cfs_rq, &rq->leaf_cfs_rq_list, leaf_cfs_rq_list)
 
 /* Do the two (enqueued) entities belong to the same group ? */
 static inline int
@@ -1132,7 +1132,9 @@ static void print_cfs_stats(struct seq_file *m, int cpu)
 #ifdef CONFIG_FAIR_GROUP_SCHED
         print_cfs_rq(m, cpu, &cpu_rq(cpu)->cfs);
 #endif
+        lock_task_group_list();
         for_each_leaf_cfs_rq(cpu_rq(cpu), cfs_rq)
                 print_cfs_rq(m, cpu, cfs_rq);
+        unlock_task_group_list();
 }
 #endif