Hi Juri!

On 05-Sep 12:45, Juri Lelli wrote:

quoted

Hi,

On 28/08/18 14:53, Patrick Bellasi wrote:

[...]

quoted

 static inline int __setscheduler_uclamp(struct task_struct *p,
 					const struct sched_attr *attr)
 {
-	if (attr->sched_util_min > attr->sched_util_max)
-		return -EINVAL;
-	if (attr->sched_util_max > SCHED_CAPACITY_SCALE)
-		return -EINVAL;
+	int group_id[UCLAMP_CNT] = { UCLAMP_NOT_VALID };
+	int lower_bound, upper_bound;
+	struct uclamp_se *uc_se;
+	int result = 0;
 
-	p->uclamp[UCLAMP_MIN] = attr->sched_util_min;
-	p->uclamp[UCLAMP_MAX] = attr->sched_util_max;
+	mutex_lock(&uclamp_mutex);

This is going to get called from an rcu_read_lock() section, which is a
no-go for using mutexes:

 sys_sched_setattr ->
   rcu_read_lock()
   ...
   sched_setattr() ->
     __sched_setscheduler() ->
       ...
       __setscheduler_uclamp() ->
         ...
	 mutex_lock()

Rightm, great catch, thanks!

quoted

Guess you could fix the issue by getting the task struct after find_
process_by_pid() in sys_sched_attr() and then calling sched_setattr()
after rcu_read_lock() (putting the task struct at the end). Peter
actually suggested this mod to solve a different issue.

I guess you mean something like this ?

---8<---

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c

@@ -5792,10 +5792,15 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr,
        rcu_read_lock();
        retval = -ESRCH;
        p = find_process_by_pid(pid);
-       if (p != NULL)
-               retval = sched_setattr(p, &attr);
+       if (likely(p))
+               get_task_struct(p);
        rcu_read_unlock();
 
+       if (likely(p)) {
+               retval = sched_setattr(p, &attr);
+               put_task_struct(p);
+       }
+
        return retval;
 }
---8<---