linux-kernel - Re: BUG NULL pointer dereference in SUNRPC xs_udp_send

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Date:	Tue, 24 Feb 2009 20:39:00 -0600
From:	Ben Myers <bpm@....com>
To:	Aaron Straus <aaron@...finllc.com>
Cc:	bfields@...ldses.org, neilb@...e.de, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, Trond.Myklebust@...app.com
Subject: Re: BUG NULL pointer dereference in SUNRPC xs_udp_send_request

Hi Aaron,

On Mon, Feb 23, 2009 at 12:11:09PM -0800, Aaron Straus wrote:
>   We received the trace below on one of our machines this weekend.   The
> machine is running vanilla 2.6.27.14.
> 
>   If I'm reading the trace correctly, it looks like this line of
> xs_udp_send_request:
> 
>    clear_bit(SOCK_ASYNC_NOSPACE, &transport->sock->flags);
> 
>   The machine is x86 (32-bit).  
> 
>   Please let me know if you need anything else e.g .config or full
> dmesg.  

That's a coincidence.  I looked at a similar bug today that crashed on
the same line but a different stack.  My suggestion is:

Index: linux/net/sunrpc/xprtsock.c
===================================================================
--- linux.orig/net/sunrpc/xprtsock.c
+++ linux/net/sunrpc/xprtsock.c
@@ -1512,14 +1512,13 @@ static void xs_udp_finish_connecting(str
                sk->sk_no_check = UDP_CSUM_NORCV;
                sk->sk_allocation = GFP_ATOMIC;

-               xprt_set_connected(xprt);
-
                /* Reset to new socket */
                transport->sock = sock;
                transport->inet = sk;

                xs_set_memalloc(xprt);

+               xprt_set_connected(xprt);
                write_unlock_bh(&sk->sk_callback_lock);
        }
        xs_udp_do_set_buffer_size(xprt);

Looks like xs_sendpages() returned -ENOTCONN.  The above should sort
that out by returning earlier in xprt_prepare_transmit() and the rpc
would be retried by __rpc_execute().

-ben
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