Re: [PATCH] netfilter: per-cpu spin-lock with recursion (v0.8)

Peter Zijlstra
2009-04-17T05:56:33Z

On Thu, 2009-04-16 at 16:52 -0700, Stephen Hemminger wrote:

> - Lockdep doesn't really handle this well

> +/**
> + * xt_table_info_lock_all - lock xt table info for update
> + *
> + * Locks out all readers, and blocks bottom half
> + */
> +void xt_table_info_lock_all(void)
> +{
> + int i;
> +
> + local_bh_disable();
> + for_each_possible_cpu(i) {
> + struct xt_lock *lock = &per_cpu(xt_info_locks, i);
> + spin_lock(&lock->lock);
> + BUG_ON(lock->depth != -1);
> + }
> +}
> +EXPORT_SYMBOL_GPL(xt_table_info_lock_all);

Quite so, this is the old MAX_LOCK_DEPTH < NR_CPUS issue for large
systems.

Last time this came up David found another way of solving the problem.
Not having fully read this thread, I cannot suggest one myself -- except
that RCU domains as suggested by David sound good.