Re: [PATCH 4/10] cpu: deliver CPU_UP_CANCELED only to NOTIFY_OKed callbacks with CPU_UP_PREPARE

Gautham R Shenoy
2007-07-18T06:54:24Z

Hi!
On Wed, Jul 18, 2007 at 02:18:41AM +0900, Akinobu Mita wrote:
> >> So it is natural to deliver CPU_UP_CANCELED event only to the functions
> >> that have returned NOTIFY_OK with CPU_UP_PREPARE event and not to call
> >> the function that have returned NOTIFY_BAD. This is what this patch is
> >doing.
> >
> >Yes, this makes sense.
>
> Thank you for making sure of it.
>
> >[...] However, it might break slab.
> >If I am not mistaken, slab code initializes multiple objects in
> >CPU_UP_PREPARE and relies on the CPU_UP_CANCELLED to destroy the
> >objects which successfully got initialized before the some object's
> >initialization went bad.
>
> My testing machine is ordinary dual core non numa box. So it might not
> trigger the problem that you are warried about under heavy slab alloc
> failure injection.
>
> At first glance I couln't find the problem in cpu hottplug code in slab.c
> yet,
> but found some memory leak path. (it doesn't break slab though)

That's what I meant. I shouldn't have used the word "break" :-)
In case of slab, freeing up of resources on an error during CPU_UP_PREPARE,
is currently handled in CPU_UP_CANCELLED.

But, like you reasoned out, it makes more sense for such a subsystem
to free up all the correctly allocated resources before sending a
NOTIFY_BAD, rather than handling it in CPU_UP_CANCELLED. And slab
needed that fix, which you've provided, before we send the notification
to (nr_calls - 1) callers.

So could you add this patch to series?

Thanks and Regards
gautham.
>
> Index: 2.6-git/mm/slab.c
> ===================================================================
> --- 2.6-git.orig/mm/slab.c
> +++ 2.6-git/mm/slab.c
> @@ -1221,13 +1221,18 @@ static int __cpuinit cpuup_callback(stru
> shared = alloc_arraycache(node,
> cachep->shared * cachep->batchcount,
> 0xbaadf00d);
> - if (!shared)
> + if (!shared) {
> + kfree(nc);
> goto bad;
> + }
> }
> if (use_alien_caches) {
> alien = alloc_alien_cache(node,
> cachep->limit);
> - if (!alien)
> - goto bad;
> + if (!alien) {
> + kfree(shared);
> + kfree(nc);
> + goto bad;
> + }
> }
> cachep->array[cpu] = nc;
> l3 = cachep->nodelists[node];

--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"