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

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Message-ID: <CA+icZUUFm0injjqR16=xz06bjm4+pCLNhtizxofE_hTxE+e==w@mail.gmail.com>
Date:	Thu, 8 Sep 2011 12:05:38 +0200
From:	Sedat Dilek <sedat.dilek@...glemail.com>
To:	Tim Chen <tim.c.chen@...ux.intel.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 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 -

[...]
>
> Tim
>
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