question regarding 2.6.18 backport

question regarding 2.6.18 backport

[Andrew Jones]

Hi Ian,

I believe there's a problem with the 2.6.18 reference tree backport of
48856286b64e: "xen/netback: shutdown the ring if it contains garbage",
which is c/s 1219. While the version in Linus' tree should be fine,
as xen_netbk_tx_action runs in a kthread, the 2.6.18 version needs
something different. In 2.6.18 net_tx_action is a tasklet, thus calling
xenvif_carrier_off from it is problematic due to needing the rtnl
mutex. A proposal I have that I haven't tried yet is for
netbk_fatal_tx_err to schedule xenvif_carrier_off in a workqueue. This
is a bit ugly though since the main point of xenvif_carrier_off is to
queue linkwatch work. I'm wondering if you or anyone else have other
suggestions.

Thanks,
Drew

Re: question regarding 2.6.18 backport

[Ian Campbell]

On Tue, 2013-02-19 at 13:51 +0000, Andrew Jones wrote:
> Hi Ian,
> 
> I believe there's a problem with the 2.6.18 reference tree backport of
> 48856286b64e: "xen/netback: shutdown the ring if it contains garbage",
> which is c/s 1219. While the version in Linus' tree should be fine,
> as xen_netbk_tx_action runs in a kthread, the 2.6.18 version needs
> something different. In 2.6.18 net_tx_action is a tasklet, thus calling
> xenvif_carrier_off from it is problematic due to needing the rtnl
> mutex. A proposal I have that I haven't tried yet is for
> netbk_fatal_tx_err to schedule xenvif_carrier_off in a workqueue. This
> is a bit ugly though since the main point of xenvif_carrier_off is to
> queue linkwatch work. I'm wondering if you or anyone else have other
> suggestions.

Jan was looking into something of this nature, not sure wht the status
is though.

Ian.

Re: question regarding 2.6.18 backport

[Jan Beulich]

>>> On 19.02.13 at 14:54, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> On Tue, 2013-02-19 at 13:51 +0000, Andrew Jones wrote:
>> Hi Ian,
>> 
>> I believe there's a problem with the 2.6.18 reference tree backport of
>> 48856286b64e: "xen/netback: shutdown the ring if it contains garbage",
>> which is c/s 1219. While the version in Linus' tree should be fine,
>> as xen_netbk_tx_action runs in a kthread, the 2.6.18 version needs
>> something different. In 2.6.18 net_tx_action is a tasklet, thus calling
>> xenvif_carrier_off from it is problematic due to needing the rtnl
>> mutex. A proposal I have that I haven't tried yet is for
>> netbk_fatal_tx_err to schedule xenvif_carrier_off in a workqueue. This
>> is a bit ugly though since the main point of xenvif_carrier_off is to
>> queue linkwatch work. I'm wondering if you or anyone else have other
>> suggestions.
> 
> Jan was looking into something of this nature, not sure wht the status
> is though.

http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/rev/ff0befcaac09

Jan