Messages in this thread Patch in this message | | | Date | Fri, 18 Apr 2014 10:19:26 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH RT V4] rwsem: The return of multi-reader PI rwsems |
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* Steven Rostedt <rostedt@goodmis.org> 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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