linux-kernel - Re: [ANNOUNCE] 3.14-rt1

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Date:	Mon, 28 Apr 2014 10:18:05 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
Cc:	Nicholas Mc Guire <der.herr@...r.at>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Kacur <jkacur@...hat.com>
Subject: Re: [ANNOUNCE] 3.14-rt1

On Mon, 28 Apr 2014 11:09:46 +0200
Mike Galbraith <umgwanakikbuti@...il.com> wrote:
 
> migrate_disable-pushd-down-in-atomic_dec_and_spin_lo.patch
> 
> bug: migrate_disable() after blocking is too late.
> 
> @@ -1028,12 +1028,12 @@ int atomic_dec_and_spin_lock(atomic_t *a
>         /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */
>         if (atomic_add_unless(atomic, -1, 1))
>                 return 0;
> -       migrate_disable();
>         rt_spin_lock(lock);
> -       if (atomic_dec_and_test(atomic))
> +       if (atomic_dec_and_test(atomic)){
> +               migrate_disable();

Makes sense, as the CPU can go offline right after the lock is grabbed
and before the migrate_disable() is called.

Seems that migrate_disable() must be called before taking the lock as
it is done in every other location.

-- Steve


>                 return 1;
> +       }
>         rt_spin_unlock(lock);
> -       migrate_enable();
>         return 0;
>  }
>  EXPORT_SYMBOL(atomic_dec_and_spin_lock);
> 
> read_lock-migrate_disable-pushdown-to-rt_read_lock.patch
> 
> bug: ditto.
> 
> @@ -244,8 +246,10 @@ void __lockfunc rt_read_lock(rwlock_t *r
>         /*
>          * recursive read locks succeed when current owns the lock
>          */
> -       if (rt_mutex_owner(lock) != current)
> +       if (rt_mutex_owner(lock) != current) {
>                 __rt_spin_lock(lock);
> +               migrate_disable();
> +       }
>         rwlock->read_depth++;
>  }
> 
> Moving that migrate_disable() up will likely fix my hotplug troubles.
> I'll find out when I get back from physical torture (therapy) session.
> 
> -Mike

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