On Wed, Dec 18, 2002 at 11:06:08PM +0000, Stephen Hemminger wrote:
> The notifier interface was only partially locked. The
> notifier_call_chain needs to be called in places where it is impossible
> to safely without having deadlocks; for example, NMI watchdog timeout.
>
> This patch uses read-copy-update to manage the list. One extra bit of
> safety is using a reference count on the notifier_blocks to allow for
> cases like oprofile which need to sleep in a callback.
>
<snip>
>
> int notifier_call_chain(struct list_head *list, unsigned long val, void
> *v)
> {
> - struct list_head *p;
> + struct list_head *p, *nxtp;
> int ret = NOTIFY_DONE;
>
> - list_for_each(p, list) {
> + rcu_read_lock();
> + list_for_each_safe_rcu(p, nxtp, list) {
> struct notifier_block *nb =
> list_entry(p, struct notifier_block, link);
>
> + atomic_inc(&nb->inuse);
> ret = nb->notifier_call(nb,val,v);
> + atomic_dec(&nb->inuse);
> +
There could be a small problem here. When rcu_read_lock() is called,
it bumps the preempt_count, so when the called handler attempts
to sleep, it will oops with "Bad: scheduling in atomic region".
-- Vamsi Krishna S. Linux Technology Center, IBM Software Lab, Bangalore. Ph: +91 80 5044959 Internet: vamsi@in.ibm.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/