sched: Protect sched_rr_get_param() access to task->sched_class

sched_rr_get_param calls
task->sched_class->get_rr_interval(task) without protection
against a concurrent sched_setscheduler() call which modifies
task->sched_class.

Serialize the access with task_rq_lock(task) and hand the rq
pointer into get_rr_interval() as it's needed at least in the
sched_fair implementation.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <alpine.LFD.2.00.0912090930120.3089@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

4 files changed, 8 insertions, 8 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index c4635f74540c..68db5a2e6545 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6887,6 +6887,8 @@ SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
 {
         struct task_struct *p;
         unsigned int time_slice;
+        unsigned long flags;
+        struct rq *rq;
         int retval;
         struct timespec t;
 
@@ -6903,7 +6905,9 @@ SYSCALL_DEFINE2(sched_rr_get_interval, pid_t, pid,
         if (retval)
                 goto out_unlock;
 
-        time_slice = p->sched_class->get_rr_interval(p);
+        rq = task_rq_lock(p, &flags);
+        time_slice = p->sched_class->get_rr_interval(rq, p);
+        task_rq_unlock(rq, &flags);
 
         read_unlock(&tasklist_lock);
         jiffies_to_timespec(time_slice, &t);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index f61837ad336d..613c1c749677 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2014,21 +2014,17 @@ static void moved_group_fair(struct task_struct *p)
 }
 #endif
 
-unsigned int get_rr_interval_fair(struct task_struct *task)
+unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task)
 {
         struct sched_entity *se = &task->se;
-        unsigned long flags;
-        struct rq *rq;
         unsigned int rr_interval = 0;
 
         /*
          * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
          * idle runqueue:
          */
-        rq = task_rq_lock(task, &flags);
         if (rq->cfs.load.weight)
                 rr_interval = NS_TO_JIFFIES(sched_slice(&rq->cfs, se));
-        task_rq_unlock(rq, &flags);
 
         return rr_interval;
 }
diff --git a/kernel/sched_idletask.c b/kernel/sched_idletask.c
index b133a28fcde3..33d5384a73a8 100644
--- a/kernel/sched_idletask.c
+++ b/kernel/sched_idletask.c
@@ -97,7 +97,7 @@ static void prio_changed_idle(struct rq *rq, struct task_struct *p,
                 check_preempt_curr(rq, p, 0);
 }
 
-unsigned int get_rr_interval_idle(struct task_struct *task)
+unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
 {
         return 0;
 }
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 5c5fef378415..aecbd9c6b20c 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1721,7 +1721,7 @@ static void set_curr_task_rt(struct rq *rq)
         dequeue_pushable_task(rq, p);
 }
 
-unsigned int get_rr_interval_rt(struct task_struct *task)
+unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
 {
         /*
          * Time slice is 0 for SCHED_FIFO tasks