netdev - Re: [PATCH net 2/2] rhashtable: Do not schedule more than one rehash if we can't grow further

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Message-ID: <20150422003744.GB5724@gondor.apana.org.au>
Date:	Wed, 22 Apr 2015 08:37:45 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	davem@...emloft.net, kaber@...sh.net, netdev@...r.kernel.org
Subject: Re: [PATCH net 2/2] rhashtable: Do not schedule more than one rehash
 if we can't grow further

On Tue, Apr 21, 2015 at 02:55:35PM +0200, Thomas Graf wrote:
> The current code currently only stops inserting rehashes into the
> chain when no resizes are currently scheduled. As long as resizes
> are scheduled and while inserting above the utilization watermark,
> more and more rehashes will be scheduled.
> 
> This lead to a perfect DoS storm with thousands of rehashes
> scheduled which lead to thousands of spinlocks to be taken
> sequentially.
> 
> Instead, only allow either a series of resizes or a single rehash.
> Drop any further rehashes and return -EBUSY.
> 
> Fixes: ccd57b1bd324 ("rhashtable: Add immediate rehash during insertion")
> Signed-off-by: Thomas Graf <tgraf@...g.ch>

Acked-by: Herbert Xu <herbert@...dor.apana.org.au>
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Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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