netdev - Re: rtnl_mutex deadlock?

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Message-ID: <20150806234117.GA22588@gondor.apana.org.au>
Date:	Fri, 7 Aug 2015 07:41:17 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Pirko <jiri@...nulli.us>,
	Cong Wang <cwang@...pensource.com>,
	David Miller <davem@...emloft.net>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Thomas Graf <tgraf@...g.ch>, Scott Feldman <sfeldma@...il.com>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: rtnl_mutex deadlock?

On Thu, Aug 06, 2015 at 04:50:39PM +0200, Daniel Borkmann wrote:
> 
> Then, in __rhashtable_insert_fast(), I could trigger an -EBUSY when I'm
> really unlucky and exceed the ht->elasticity limit of 16. I would then
> end up in rhashtable_insert_rehash() to find out there's already one
> ongoing and thus, I'm getting -EBUSY via __netlink_insert().

Right, so the only way you can trigger this is if you hit a chain
longer than 16 and the number of entries in the table is less than
75% the size of the table, as well as there being an existing resize
or rehash operation.

This should be pretty much impossible.

But if we had a WARN_ON_ONCE there then we'll know for sure.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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