On 08/09, Manfred Spraul wrote:
>
> /*
> + * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
> + * are only control barriers.
> + * The code must pair with spin_unlock(&sem->lock) or
> + * spin_unlock(&sem_perm.lock), thus just the control barrier is
> insufficient.
> + *
>
On Sun, Aug 09, 2015 at 07:55:39PM +0200, Manfred Spraul wrote:
> sem_lock() did not properly pair memory barriers:
>
> !spin_is_locked() and spin_unlock_wait() are both only control barriers.
> The code needs an acquire barrier, otherwise the cpu might perform
> read operations before the lock te
Manfred,
I leave this to you and Paul/Peter, but...
On 03/01, Manfred Spraul wrote:
>
> +/*
> + * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
> + * are only control barriers, thus a memory barrier is required if the
> + * operation should act as an acquire memory barrie
Hi Oleg,
On 03/01/2015 02:22 PM, Oleg Nesterov wrote:
On 02/28, Peter Zijlstra wrote:
On Sat, Feb 28, 2015 at 09:36:15PM +0100, Manfred Spraul wrote:
+/*
+ * Place this after a control barrier (such as e.g. a spin_unlock_wait())
+ * to ensure that reads cannot be moved ahead of the control_bar
On 02/28, Paul E. McKenney wrote:
>
> The idea is that this would become a no-op on x86, s390, sparc &c, an isb
> instruction on ARM, an isync instruction on Power, and I cannot remember
> what on Itanium? The other idea being to provide read-to-read control
> ordering in addition to the current r
On 02/28, Peter Zijlstra wrote:
>
> On Sat, Feb 28, 2015 at 09:36:15PM +0100, Manfred Spraul wrote:
> > +/*
> > + * Place this after a control barrier (such as e.g. a spin_unlock_wait())
> > + * to ensure that reads cannot be moved ahead of the control_barrier.
> > + * Writes do not need a barrier,
On Sat, Feb 28, 2015 at 10:45:33PM +0100, Peter Zijlstra wrote:
> On Sat, Feb 28, 2015 at 09:36:15PM +0100, Manfred Spraul wrote:
> > +/*
> > + * Place this after a control barrier (such as e.g. a spin_unlock_wait())
> > + * to ensure that reads cannot be moved ahead of the control_barrier.
> > + *
On Sat, Feb 28, 2015 at 09:36:15PM +0100, Manfred Spraul wrote:
> +/*
> + * Place this after a control barrier (such as e.g. a spin_unlock_wait())
> + * to ensure that reads cannot be moved ahead of the control_barrier.
> + * Writes do not need a barrier, they are not speculated and thus cannot
> +
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