Date:	Mon, 10 Feb 2014 07:08:05 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Wang Weidong <wangweidong1@...wei.com>
Cc:	davem@...emloft.net, vyasevich@...il.com, dborkman@...hat.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH 0/2] sctp: fix a problem with net_namespace

On Mon, Feb 10, 2014 at 10:56:51AM +0800, Wang Weidong wrote:
> On 2014/1/28 19:57, Neil Horman wrote:
> > On Tue, Jan 28, 2014 at 04:13:44PM +0800, Wang Weidong wrote:
> >> On 2014/1/27 19:49, Neil Horman wrote:
> >>> On Mon, Jan 27, 2014 at 11:49:01AM +0800, Wang Weidong wrote:
> >>>> fix a problem with net_namespace, and optimize
> >>>> the sctp_sysctl_net_register.
> >>>>
> >>>> Wang Weidong (2):
> >>>>   sctp: fix a missed .data initialization
> >>>>   sctp: optimize the sctp_sysctl_net_register
> >>>>
> >>>>  net/sctp/sysctl.c | 17 ++++++++++-------
> >>>>  1 file changed, 10 insertions(+), 7 deletions(-)
> >>>>
> >>>> -- 
> >>>> 1.7.12
> >>>>
> >>>>
> >>>>
> >>> I don't see that either of these patches are needed.  In sctp_init_net, the
> >>> sctp_hmac_alg pointer gets initalized before calling sctp_sysctl_net_register,
> >>> and sctp_proc_do_hmac_alg is written to specifically expect NULL values, so this
> >>> code may change behavior regarding default cookie selection.
> >>>
> >> Hi Neil,
> >>
> >> Here, I think the sctp_proc_do_hmac_alg will be called only when we change the 
> >> /proc/sys/net/cookie_hmac_alg. So add the .data won't effect the default value.
> >> and the data isn't equal to the "cookie_hmac_alg"?
> >>
> >>> This was coded so that poniters to entires in the string table could be used,
> >>> rather than needing to allocate or maintain character buffers.  That said, it
> >>> does look like that for loop in sctp_sysctl_register_table might compute an odd
> >>> offset when cloning the table.  I think the right fix for that is likely to just
> >>> move the sysctl value initalization in sctp_init_net to below the sysctl
> >>> register function.
> >>>
> >>> Neil
> >>>
> >>
> >> I found the problem is that:
> >> I use "ip netns add netns1/netns2"
> >> In any netns(netns1 or netns2 or init_net) when I change the value of the entry
> >> such as "addip_enable" "max_autoclose" which after the cookie_hmac_alg (contain it),
> >> and the other netns will be effected.
> >>
> >> In sctp_sysctl_net_register, kmemdup does cloning the table. The offset of netns1 and
> >> init_net's clt_table.data is the same as two netns offset. So the for(){...} would do
> >> add the offset for every clt_table.data.
> >>
> >> The code:
> >> 	for (i = 0; table[i].data; i++)
> >> 		table[i].data += (char *)(&net->sctp) - (char *)&init_net.sctp;
> >>
> >> And I add a pr_info into the for(){...} in sctp_sysctl_net_register and only print 7 times for each ns.
> >> 7 is the index of "cookie_preserve_enable" which before the "cookie_hmac_alg". 
> >>
> >> As the "cookie_hmac_alg" data is NULL, so we can't add offset to the rest, and all the netns use the same
> >> address of clt_table entry after the "cookie_hmac_alg".
> >>
> >> So I think only "move the sysctl value initalization in sctp_init_net to below the sysctl
> >> register function" won't solve the problem, because the problem is at the for() {...}.
> >>
> > I'm sorry, you're right, the kmemdup duplicates the table, not the structure in
> > which the table points to with its .data pointers.  I was looking at it
> > backwards.
> > 
> 
> Hi Neil,
> 
> Should I resend "sctp: fix a problem with net_namespace" series again?
> 
Not sure.  I agree with your assesment on the table adjustments, but I think the
discussion below is holding things up.  You probably want to get to the root
cause of whats causing the lockdep issue before that patch goes in

for 1/2 though
Acked-by: Neil Horman <nhorman@...driver.com>

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