Messages in this thread | | | Date | Fri, 19 Aug 2011 21:31:05 -0400 | Subject | Re: [PATCH RFC] rtmutex: Permit rt_mutex_unlock() to be invoked with irqs disabled | From | Arnaud Lacombe <> |
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Hi,
On Sun, Jul 24, 2011 at 11:56 AM, Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > On Sun, Jul 24, 2011 at 11:00:41AM +0200, Thomas Gleixner wrote: >> On Sat, 23 Jul 2011, Paul E. McKenney wrote: >> > On Sun, Jul 24, 2011 at 02:05:13AM +0200, Thomas Gleixner wrote: >> > > On Sun, 24 Jul 2011, Thomas Gleixner wrote: >> > > > > > Thomas, I'm inclined to merge this, any objections? >> > > > > >> > > > > FWIW, it has been passing tests here. >> > > > >> > > > If it's only the unlock path, I'm fine with that change. >> > > > >> > > > Acked-by-me >> > > >> > > Hrmpft. That's requiring all places to take the lock irq safe. Not >> > > really amused. For -RT that's a hotpath and we can really do without >> > > the irq fiddling there. That needs a bit more thought. >> > >> > Indeed... If I make only some of the lock acquisitions irq safe, lockdep >> > will yell at me. And rightfully so, as that could result in deadlock. >> > >> > So, what did you have in mind? >> >> Have no real good idea yet for this. Could you grab rt and check >> whether you can observe any impact when the patch is applied? > > Hmmm, wait a minute... There might be a way to do this with zero > impact on the fastpath, given that I am allocating an rt_mutex on > the stack that is used only by RCU priority boosting, and that only > rt_mutex_init_proxy_locked(), rt_mutex_lock(), and rt_mutex_unlock() > are used. > > So I could do the following: > > o Use lockdep_set_class_and_name() to make the ->wait_lock() > field of my rt_mutex have a separate lockdep class. I guess > I should allocate a global variable for lock_class_key > rather than allocating it on the stack. ;-) > > o Make all calls from RCU priority boosting to rt_mutex_lock() > and rt_mutex_unlock() have irqs disabled. > > o Make __rt_mutex_slowlock() do the following when sleeping: > > raw_spin_unlock(&lock->wait_lock); > > debug_rt_mutex_print_deadlock(waiter); > > { > int was_disabled = irqs_disabled(); > > if (was_disabled) > local_irq_enable(); > FWIW, the final construct you opted for in -next:
if (was_disabled = irqs_disabled()) local_irq_enable();
triggers:
/linux/linux/kernel/rtmutex.c: In function '__rt_mutex_slowlock': /linux/linux/kernel/rtmutex.c:605:3: warning: suggest parentheses around assignment used as truth value
- Arnaud
> schedule_rt_mutex(lock); > > if (was_disabled) > local_irq_disable(); > > } > > raw_spin_lock(&lock->wait_lock); > set_current_state(state); > > Would that work reasonably? > > Thanx, Paul > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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