netdev - Re: [PATCH -next v2] unix stream: Fix use-after-free crashes

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Date:	Thu, 08 Sep 2011 01:50:54 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	sedat.dilek@...il.com
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
	"jirislaby@...il.com" <jirislaby@...il.com>, alex.shi@...el.com
Subject: Re: [PATCH -next v2] unix stream: Fix use-after-free crashes

On Thu, 2011-09-08 at 12:05 +0200, Sedat Dilek wrote:
> On Tue, Sep 6, 2011 at 9:59 PM, Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> > On Tue, 2011-09-06 at 21:43 +0200, Eric Dumazet wrote:
> >> Le mardi 06 septembre 2011 à 12:33 -0700, Tim Chen a écrit :
> >>
> >> > Yes, I think locking the sendmsg for the entire duration of
> >> > unix_stream_sendmsg makes a lot of sense.  It simplifies the logic a lot
> >> > more.  I'll try to cook something up in the next couple of days.
> >>
> >> Thats not really possible, we cant hold a spinlock and call
> >> sock_alloc_send_skb() and/or memcpy_fromiovec(), wich might sleep.
> >>
> >> You would need to prepare the full skb list, then :
> >> - stick the ref on the last skb of the list.
> >>
> >> Transfert the whole skb list in other->sk_receive_queue in one go,
> >> instead of one after another.
> >>
> >> Unfortunately, this would break streaming (big send(), and another
> >> thread doing the receive)
> >>
> >> Listen, I am wondering why hackbench even triggers SCM code. This is
> >> really odd. We should not have a _single_ pid/cred ref/unref at all.
> >>
> >
> > Hackbench triggers the code because it has a bunch of threads sending
> > msgs on UNIX socket.
> >>
> >
> 
> # lsof | grep socket | wc -l
> 198
> 
> Aprrox 200 sockets in usage here, can you post your hackbench line, please?
> I would compare hackbench results with and without new improvements in SCM code.
> 
> - Sedat -
> 

The hackbench line I used was

./hackbench 50 thread 2000

You will need to use the threaded case for testing to see the issue.  I
was running on a 4 socket, 40 cores total Westmere-EX machine.  The
improvement may depend on your machine size, probably with more
improvement on larger multi-socket machine as smaller ones don't have as
big a problem.

Tim


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