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

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Message-ID: <CADvbK_df=Z1re2wPUF9JCXggBzRqF=Tgt86PXV0KqBcx3VeVNA@mail.gmail.com>
Date:	Thu, 17 Dec 2015 17:00:35 +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 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. :)
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