netdev - Re: rhashtable: Prevent spurious EBUSY errors on insertion

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Message-ID: <CADvbK_e_H91UAatLSOEAvPFxZZTNNs5ZFR5TieXBdWt65z4Qzg@mail.gmail.com>
Date:	Fri, 18 Dec 2015 00:07:08 +0800
From:	Xin Long <lucien.xin@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Phil Sutter <phil@....cc>, davem <davem@...emloft.net>,
	network dev <netdev@...r.kernel.org>,
	linux-kernel@...r.kernel.org, tgraf@...g.ch,
	fengguang.wu@...el.com, wfg@...ux.intel.com, lkp@...org
Subject: Re: rhashtable: Prevent spurious EBUSY errors on insertion

On Thu, Dec 17, 2015 at 5:00 PM, Xin Long <lucien.xin@...il.com> wrote:
> On Thu, Dec 17, 2015 at 4:48 PM, Herbert Xu <herbert@...dor.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.
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