netdev - Re: Fix for the fundamental network/block layer race in sendfile().

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Message-ID: <20080401174759.GB28217@2ka.mipt.ru>
Date:	Tue, 1 Apr 2008 21:47:59 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	David Miller <davem@...emloft.net>, axboe@...nel.dk,
	netdev@...r.kernel.org
Subject: Re: Fix for the fundamental network/block layer race in sendfile().

Hi.

On Tue, Apr 01, 2008 at 07:19:39PM +0200, Eric Dumazet (dada1@...mosbay.com) wrote:
> >@@ -762,6 +765,12 @@ static ssize_t do_sendfile(int out_fd, int in_fd, 
> >loff_t *ppos,
> > 		count = max - pos;
> > 	}
> > 
> >+	sock = out_file->private_data;
> >+	sk = sock->sk;
> >+
> >+	sk->sk_user_data = &skb_splice_destructor;
> >+	sk->sk_flags |= SO_PRIVATE_CALLBACK;
> 
> Ouch...
> 
> this seems very ugly (sorry).
> 
> 1) Is out_file garanted to be a socket ?

Yep.

> 2) SO_PRIVATE_CALLBACK is defined to be 37 later on your patch. Is ORing 37 
> to sk_flags really working ???

Kind of... Not as supposed to be, since sk_flags is a long.
Will put that flag into socket instead.

> 3) So, once a socket has been used for a sendfile(), all subsequent 
> sendmsg() will call skb_splice_destructor ? (I see no clearing of 
> SO_PRIVATE_CALLBACK)
>  This will probably crash.

Yep, need to clear.

> 4) god_blessed_us name ... Oh I got it, its April the first !!!!

But it still works :)

-- 
	Evgeniy Polyakov
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