linux-kernel - Re: rhashtable: how to deal with that rhashtable_lookup_insert

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Date:	Fri, 20 Nov 2015 13:24:01 +0100
From:	Phil Sutter <phil@....cc>
To:	Xin Long <lucien.xin@...il.com>
Cc:	linux-kernel@...r.kernel.org, network dev <netdev@...r.kernel.org>,
	tgraf@...g.ch, herbert@...dor.apana.org.au,
	davem <davem@...emloft.net>
Subject: Re: rhashtable: how to deal with that rhashtable_lookup_insert_key
 return -EBUSY

On Fri, Nov 20, 2015 at 01:14:18PM +0800, Xin Long wrote:
> when I use rhashtable_lookup_insert_key, sometimes it will return -EBUSY.
> im not sure if there is a good way to workabout it.
> or I should just try again and again until it's inserted successfully ?
> 
> I have seen some use in kernel  by now, but it seems that no one consider
> this issue for their cases. but it indeed exists in my case.
> 
> did I use it incorrectly or something else ?

AFAIK, insert returning -EBUSY is a situation users have to be aware of
and retry the insert. I sent a patch[1] to fix this in test_rhashtable.

That patch though retried in case of -ENOMEM as well, which was
considered wrong to do and therefore it wasn't accepted. But in my test
runs, -ENOMEM happened quite frequently and it also wasn't a permanent
error. For details, see the following discussion[2].

Herbert, did you manage to reproduce the problem meanwhile? If so, was
there any progress on fixing rhashtable? Otherwise, I could respin my
patch from [1] to cover only -EBUSY case by default and add a parameter
to make non-permanent -ENOMEM visible.

Cheers, Phil

[1]: https://lkml.org/lkml/2015/8/28/197
[2]: https://lkml.org/lkml/2015/8/28/281
> 
> Thanks.
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