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SubjectRe: [PATCH 4/6] rhashtable: allow a walk of the hash table without missing objects.
On Tue, Mar 27 2018, Herbert Xu wrote:

> On Tue, Mar 27, 2018 at 10:33:04AM +1100, NeilBrown wrote:
>> -int rhashtable_walk_start_check(struct rhashtable_iter *iter)
>> +int rhashtable_walk_start_continue(struct rhashtable_iter *iter, struct rhash_head *obj)
>> __acquires(RCU)
>> {
>> struct rhashtable *ht = iter->ht;
>> rcu_read_lock();
>> + if (!obj || iter->p != obj)
>> + iter->p = NULL;
> Why bother with this check at all? Couldn't we make it so that
> if you call continue then you continue with the cursor otherwise
> you set it to NULL as we currently do.

I particularly want the interface to require that you pass the
previously returned object to _continue. That makes it easy to see that
the object is still being used. If someone changes to code to delete
the object before the _continue, there should be a strong hint that it
won't work.

Maybe it would be better to make it a WARN_ON()

if (!obj || WARN_ON(iter->p != obj))
iter->p = NULL;


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