On Mon, Sep 26, 2016 at 11:35:03AM -0400, Steven Rostedt wrote: > On Mon, 26 Sep 2016 17:22:28 +0200 > Peter Zijlstra <pet...@infradead.org> wrote: > > > > > + /* > > > > + * We should deboost before waking the top waiter task such that > > > > + * we don't run two tasks with the 'same' priority. This however > > > > + * can lead to prio-inversion if we would get preempted after > > > > + * the deboost but before waking our high-prio task, hence the > > > > + * preempt_disable before unlock. Pairs with preempt_enable() in > > > > + * rt_mutex_postunlock(); > > > > > > There's a preempt_enable() in rt_mutex_postunlock()? Does > > > wake_futex_pi() know that? > > > > > > > Not sure I see your point. rt_mutex_futex_unlock() calls > > rt_mutex_slowunlock() which does the preempt_disable(), we then pass the > > return of that into deboost, which we pass into rt_mutex_postunlock() > > and everything should be balanced. > > Can we please add more comments explaining this. Having side effects of > functions disabling preemption, passing a bool saying that it did, and > needing to call another function (somewhat seemingly unrelated) to > re-enable preemption, just seems a bit of a stretch for maintainable > code. > > Especially now that the code after the spin_unlock(&hb->lock) is now a > critical section (preemption is disable). There's nothing obvious in > futex.c that says it is. > > Just think about looking at this code in another 5 years. Are you going > to remember all this?
There's some cleanups later in the series that should clear this up.
