Messages in this thread | | | Date | Thu, 21 Sep 2017 19:35:12 +0200 | From | Sebastian Andrzej Siewior <> | Subject | Re: [PATCH RT] locking/rtmutex: don't drop the wait_lock twice |
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On 2017-09-21 12:50:27 [-0400], Steven Rostedt wrote: > On Thu, 21 Sep 2017 18:43:02 +0200 > Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote: > > > On 2017-09-21 12:31:05 [-0400], Steven Rostedt wrote: > > > > diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c > > > > index f03876322d4a..79f49d73e4d0 100644 > > > > --- a/kernel/locking/rtmutex.c > > > > +++ b/kernel/locking/rtmutex.c > > > > @@ -2281,7 +2281,6 @@ int __rt_mutex_start_proxy_lock(struct rt_mutex *lock, > > > > raw_spin_lock(&task->pi_lock); > > > > if (task->pi_blocked_on) { > > > > raw_spin_unlock(&task->pi_lock); > > > > - raw_spin_unlock_irq(&lock->wait_lock); > > > > > > Hmm, before this patch, irqs are enabled when returning with -EAGAIN. > > > But now they are not. Should that be: > > > > > > raw_spin_unlock_irq(&taks->pi_lock); > > > > > > or is there something that changes this? > > > > There is something else. Before that futex rework there was just > > rt_mutex_start_proxy_lock() and it did lock & unlock of ->wait_lock. > > This no longer the case after the rework. So now the caller does this. > > > > So this actually fixes two bugs then? Anyway, probably want to add that > in the change log to explain why it is ok to change the irq semantics > here too.
No, it does not. It fixes only one and this one was introduced while I rebased RT ontop of the futex work - the patch "futex: Fix bug on when a requeued RT task times out" to be exact. If you look at the code in the v4.9 or v4.11 RT then you see that there is just rt_mutex_start_proxy_lock()() and this function acquires and releases ->wait_lock lock. After the futex rework the locking changed and I missed to adapt the RT-only patch I mentioned. Again: without the patch, the ->wait_lock is dropped twice in the error case here: once here and the second time by the caller and this has only been like this since the futex-rework. So this does not apply to v4.1-RT for instance because the futex rework got into v4.9.18-rt14 and I don't recall that you backported it.
> Thanks! > > -- Steve
Sebastian
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