Messages in this thread | | | Date | Sat, 28 Oct 2006 09:49:31 -0700 | From | Andrew Morton <> | Subject | Re: [rfc] [patch] mm: Slab - Eliminate lock_cpu_hotplug from slab |
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On Fri, 27 Oct 2006 18:19:19 -0700 Ravikiran G Thirumalai <kiran@scalex86.org> wrote:
> Another note. Looks like a cpu hotplug event can send CPU_UP_CANCELED to > a registered subsystem even if the subsystem did not receive CPU_UP_PREPARE. > This could be due to a subsystem registered for notification earlier than > the current subsystem crapping out with NOTIFY_BAD. Badness can occur with > in the CPU_UP_CANCELED code path at slab if this happens (The same would > apply for workqueue.c as well).
yup, cancellation doesn't work at present.
> To overcome this, we might have to use either > a) a per subsystem flag and avoid handling of CPU_UP_CANCELED, or > b) Use a special notifier events like LOCK_ACQUIRE/RELEASE as Gautham was > using in his experiments, or > c) Do not send CPU_UP_CANCELED to a subsystem which did not receive > CPU_UP_PREPARE. > > I would prefer c).
c) would work. I guess we could do that by simply counting the number of called handlers rather than having to record state within each one.
It would require changes to the notifier_chain API, but I think the changes are needed - the problem is general. Something like:
int __raw_notifier_call_chain(struct raw_notifier_head *nh, unsigned long val, void *v, unsigned nr_to_call, int *nr_called);
int raw_notifier_call_chain(struct raw_notifier_head *nh, unsigned long val, void *v) { return __raw_notifier_call_chain(nh, val, v, -1, NULL); }
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