netdev - Re: [PATCH] ipv4: synchronize bind() with RTM

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Date:	Thu, 21 Oct 2010 04:03:19 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	timo.teras@....fi
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv4: synchronize bind() with RTM_NEWADDR notifications

From: Timo Teräs <timo.teras@....fi>
Date: Thu, 21 Oct 2010 13:58:08 +0300

> On 10/21/2010 01:50 PM, David Miller wrote:
>> From: Timo Teräs <timo.teras@....fi>
>> Date: Thu, 21 Oct 2010 13:41:37 +0300
>> 
>>> Is inet_bind() called from non-userland context? If yes, then this is a
>>> bad idea. Otherwise I don't think it's that hot path...
>> 
>> It is.
> 
> Yet, almost immediately after that there is lock_sock() which can also
> sleep. How does that work then?

RTNL interlocks globally with a heavy primitive, a mutex, lock_sock()
grabs a spinlcok which is local to the socket's context.

So if we have 100,000 sockets binding we'll suck with you're change
whereas the lock_sock() does not cause that problem.

Is this so difficult for you to comprehend?
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