netdev - Re: [PATCH] rhashtable: don't attempt to grow when at max

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Message-Id: <20150423.115919.1353583175267783165.davem@davemloft.net>
Date:	Thu, 23 Apr 2015 11:59:19 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	johannes@...solutions.net
Cc:	netdev@...r.kernel.org, kaber@...sh.net, tgraf@...g.ch,
	johannes.berg@...el.com, herbert@...dor.apana.org.au
Subject: Re: [PATCH] rhashtable: don't attempt to grow when at max_size

From: Johannes Berg <johannes@...solutions.net>
Date: Thu, 23 Apr 2015 16:38:43 +0200

> From: Johannes Berg <johannes.berg@...el.com>
> 
> The conversion of mac80211's station table to rhashtable had a bug
> that I found by accident in code review, that hadn't been found as
> rhashtable apparently managed to have a maximum hash chain length
> of one (!) in all our testing.
> 
> In order to test the bug and verify the fix I set my rhashtable's
> max_size very low (4) in order to force getting hash collisions.
> 
> At that point, rhashtable WARNed in rhashtable_insert_rehash() but
> didn't actually reject the hash table insertion. This caused it to
> lose insertions - my master list of stations would have 9 entries,
> but the rhashtable only had 5. This may warrant a deeper look, but
> that WARN_ON() just shouldn't happen.
> 
> Fix this by not returning true from rht_grow_above_100() when the
> rhashtable's max_size has been reached - in this case the user is
> explicitly configuring it to be at most that big, so even if it's
> now above 100% it shouldn't attempt to resize.
> 
> This fixes the "lost insertion" issue and consequently allows my
> code to display its error (and verify my fix for it.)
> 
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>

It looks fine to me, but I'll let Herbert and Thomas review this.
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