* Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> Changes since v3:
>
> Clark reported that he was seeing a large latency when he added this
> patch. I tested it out on a 8 logical CPU box, and sure enough I was
> seeing it too. After spending the day debugging why, I found that I had
> a bug in rt_mutex_getprio(), where I could do:
>
> min(task_top_pi_waiter(task)->pi_list_entry.prio, prio)
>
> when there was no "top_pi_waiter", which would give garbage as a
> result. This would let some tasks have higher priority than they
> should, and cause other tasks that should have high priority not run.
Would a sanity check like the one below have helped? (untested and
such)
Thanks,
Ingo
==========>
kernel/locking/rtmutex_common.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 7431a9c..36b1ce8 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -85,6 +85,7 @@ static inline int task_has_pi_waiters(struct task_struct *p)
static inline struct rt_mutex_waiter *
task_top_pi_waiter(struct task_struct *p)
{
+ WARN_ON_ONCE(!p->pi_waiters_leftmost);
return rb_entry(p->pi_waiters_leftmost, struct rt_mutex_waiter,
pi_tree_entry);
}
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