Messages in this thread | | | Date | Tue, 14 Jun 2016 18:39:08 +0100 | From | Juri Lelli <> | Subject | Re: [RFC][PATCH 8/8] rtmutex: Fix PI chain order integrity |
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On 07/06/16 21:56, Peter Zijlstra wrote: > rt_mutex_waiter::prio is a copy of task_struct::prio which is updated > during the PI chain walk, such that the PI chain order isn't messed up > by (asynchronous) task state updates. > > Currently rt_mutex_waiter_less() uses task state for deadline tasks; > this is broken, since the task state can, as said above, change > asynchronously, causing the RB tree order to change without actual > tree update -> FAIL. > > Fix this by also copying the deadline into the rt_mutex_waiter state > and updating it along with its prio field. > > Ideally we would also force PI chain updates whenever DL tasks update > their deadline parameter, but for first approximation this is less > broken than it was. >
The patch looks OK to me. However, I'm failing to see when we can update dl.deadline of a waiter asynchronously. Since a waiter is blocked, we can't really change his dl.deadline by calling setscheduler on him, as the update would operate on dl.dl_deadline. The new values will start to be used as soon as it gets unblocked. The situation seems different for RT tasks, for which priority change takes effect immediately.
What am I missing? :-)
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