Messages in this thread Patch in this message | | | Date | Sat, 20 Aug 2011 10:09:32 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC] rtmutex: Permit rt_mutex_unlock() to be invoked with irqs disabled |
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On Fri, Aug 19, 2011 at 09:31:05PM -0400, Arnaud Lacombe wrote: > 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
But I -do- have parentheses around that assignment!!!
Sigh, gcc strikes again. Does the following patch help? If so, I will fold it into commit 83841f02.
Thanx, Paul
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Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c index 0222e34..2548f44 100644 --- a/kernel/rtmutex.c +++ b/kernel/rtmutex.c @@ -602,7 +602,8 @@ __rt_mutex_slowlock(struct rt_mutex *lock, int state, raw_spin_unlock(&lock->wait_lock); - if (was_disabled = irqs_disabled()) + was_disabled = irqs_disabled(); + if (was_disabled) local_irq_enable(); debug_rt_mutex_print_deadlock(waiter); -- 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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