Re: rhashtable: Prevent spurious EBUSY errors on insertion

Xin Long
2015-12-17T16:07:12Z

On Thu, Dec 17, 2015 at 5:00 PM, Xin Long <lucien.xin@gmail.com> wrote:
> On Thu, Dec 17, 2015 at 4:48 PM, Herbert Xu <herbert@gondor.apana.org.au> wrote:
>> On Thu, Dec 17, 2015 at 04:46:00PM +0800, Xin Long wrote:
>>>
>>> sorry for late test, but unfortunately, my case with rhashtalbe still
>>> return EBUSY.
>>> I added some debug code in rhashtable_insert_rehash(), and found:
>>> *future_tbl is null*
>>>
>>> fail:
>>> /* Do not fail the insert if someone else did a rehash. */
>>> if (likely(rcu_dereference_raw(tbl->future_tbl))) {
>>> printk("future_tbl is there\n");
>>> return 0;
>>> } else {
>>> printk("future_tbl is null\n");
>>> }
>>>
>>> any idea why ?
>>
>> That's presumably because you got a genuine double rehash.
>>
>> Until you post your code we can't really help you.
>>
> i wish i could , but my codes is a big patch for sctp, and this issue
> happens in a special stress test based on this patch.
> im trying to think how i can show you. :)

I'm just wondering, why do not we handle the genuine double rehash
issue inside rhashtable? i mean it's just a temporary error that a
simple retry may fix it.