netdev - Re: nfs client lockdep warning

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Date:	Fri, 9 Jan 2009 15:29:39 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>, netdev@...r.kernel.org,
	linux-nfs@...r.kernel.org, Trond Myklebust <trond@...app.com>,
	Ingo Molnar <mingo@...e.hu>, Nick Piggin <npiggin@...e.de>
Subject: Re: nfs client lockdep warning

On Fri, Jan 09, 2009 at 07:51:08AM +0100, Peter Zijlstra wrote:
> On Fri, 2009-01-09 at 17:23 +1100, Herbert Xu wrote:
> > On Fri, Jan 09, 2009 at 06:58:17AM +0100, Peter Zijlstra wrote:
> > >
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c054bb26>] copy_from_user+0x36/0x90
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c0737800>] memcpy_fromiovecend+0x60/0x90
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c075ce9f>] ip_generic_getfrag+0x9f/0xb0
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c075cb6b>] ip_append_data+0x6bb/0x950
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c077cb0d>] udp_sendmsg+0x2bd/0x680
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c07835f9>] inet_sendmsg+0x39/0x70
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c072f0e6>] sock_sendmsg+0xd6/0x100
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c072f485>] kernel_sendmsg+0x35/0x50
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c07da698>] xs_send_kvec+0xa8/0xb0
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c07da711>] xs_sendpages+0x71/0x210
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c07dab30>] xs_udp_send_request+0x40/0x120
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c07d91ff>] xprt_transmit+0x6f/0x280
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c07d6c1f>] call_transmit+0x17f/0x250
> > > > > > > Jan  8 15:29:17 ying3 kernel:        [<c07dda13>] __rpc_execute+0x73/0x250
> > > 
> > > Is there anything pinning that user-space page, if not its free to
> > > fault, which would mean its a real warning... 
> > 
> > It's kernel memory, not user memory.  See xs_udp_send_request in
> > net/sunrpc.
> 
> Ahh, so something like this ought to fix it I think...
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
> diff --git a/mm/memory.c b/mm/memory.c
> index 7b9db65..a2ed52e 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3079,6 +3079,9 @@ void print_vma_addr(char *prefix, unsigned long ip)
>  #ifdef CONFIG_PROVE_LOCKING
>  void might_fault(void)
>  {
> +	if (get_fs() == KERNEL_DS)

Looks like that should be

	if ((segment_eq(get_fs(), KERNEL_DS))

?  Anyway, with that, sure, that eliminates the lockdep warning.

--b.

> +		return;
> +
>  	might_sleep();
>  	/*
>  	 * it would be nicer only to annotate paths which are not under
> 
> 
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