On Wed, Sep 04, 2013 at 07:09:04PM +0100, Christoph Lameter wrote:
> On Wed, 4 Sep 2013, Will Deacon wrote:
>
> > On ARM, yes. I'm worried that there may be an architecture where the change-
> > or-fail operation would only fail if the access from the interrupt handler
> > *also* used that change-or-fail instruction, which isn't the case with
> > this_cpu_inc.
> >
> > I have no idea if such an architecture exists :)
>
> Atomic operations use atomic_t. this_cpu operations can only use regular
> scalars. So the set of variables that are updated by each should be
> distinct.
Right, except that your patch contained the following hunk:
Index: linux/arch/arm64/kernel/debug-monitors.c
===================================================================
--- linux.orig/arch/arm64/kernel/debug-monitors.c 2013-08-26
13:48:40.956794980 -0500
+++ linux/arch/arm64/kernel/debug-monitors.c 2013-08-26 13:48:40.952795024
-0500
@@ -98,11 +98,11 @@ void enable_debug_monitors(enum debug_el
WARN_ON(preemptible());
- if (local_inc_return(&__get_cpu_var(mde_ref_count)) == 1)
+ if (this_cpu_inc_return(mde_ref_count) == 1)
enable = DBG_MDSCR_MDE;
if (el == DBG_ACTIVE_EL1 &&
- local_inc_return(&__get_cpu_var(kde_ref_count)) == 1)
+ this_cpu_inc_return(kde_ref_count) == 1)
enable |= DBG_MDSCR_KDE;
if (enable && debug_enabled) {
Then we have:
#define local_inc_return(l) atomic_long_inc_return(&(l)->a)
static inline long atomic_long_inc_return(atomic_long_t *l)
{
atomic_t *v = (atomic_t *)l;
return (long)atomic_inc_return(v);
}
So that casting lets the two interfaces overlap (and indeed they do after
your patch, since local_dec_and_test is still used to the same variable).
Will
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