Re: [Xen-devel] Xen-unstable Linux 3.14-rc3 and 3.13 Network troubles "bisected"

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

Tuesday, March 11, 2014, 1:38:07 PM, you wrote:

> On Tue, Mar 11, 2014 at 01:31:42PM +0100, Sander Eikelenboom wrote:
>> 
>> Tuesday, March 11, 2014, 11:19:48 AM, you wrote:
>> 
>> > On Tue, Mar 11, 2014 at 12:00:26AM +0100, Sander Eikelenboom wrote:
>> > [...]
>> >> 
>> >> >> Wei.
>> >> 
>> >> Hi Paul,
>> >> 
>> >> It seems a commit by you: "ca2f09f2b2c6c25047cfc545d057c4edfcfe561c 
>> >> xen-netback: improve guest-receive-side flow control"
>> >> is the first that gives the Bad grant references.
>> >> It seems later patches partly prevent or mask the issue, so it is less 
>> >> easy to trigger it.
>> >> With only this commit applied i can trigger it quite fast.
>> >> 
>> >> This is the result of:
>> >> - First testing a baseline that worked o.k. for several days (3.13.6 for 
>> >> both dom0 and domU)
>> >> - Testing domU 3.14-rc5 and dom0 3.13.6, this worked ok.
>> >> - Testing dom0 3.14-rc5 and domU 3.13.6, this failed.
>> >> - After that took 3.13.6 as base and first applied all the general xen 
>> >> related patches for the dom0 kernel, that works ok.
>> >> - After that started to apply the netback changes for 3.14 and that 
>> >> failed after the commit stated above.
>> >> 
>> >> So i'm quite confident i'm reporting the right thing now :-)
>> >> If you would like me to run debug patches on top of this commit, don't 
>> >> hesitate to send them !
>> >> 
>> 
>> > Hmm.... I just looked at the commit, something that's obvious wrong is
>> > the use of gso_type to determine whether an extra slot is required,
>> > which is fixed by Annie yesterday. Annie fixed that for netback.c but
>> > missed interface.c.
>> 
>> > This can probably fix the problem you're seeing. I will submit a proper
>> > patch if you confirm that...
>> 
>> Although the patch seems correct in it's own right .. it doesn't seem to fix

> I will submit that patch anyway...

>> the issue when using 3.13.6 as a base and ..
>>   - pull all 3.14 patches from the  
>> git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git tree
>>   - apply paul's commit "ca2f09f2b2c6c25047cfc545d057c4edfcfe561c 
>> xen-netback: improve guest-receive-side flow control"
>>   - applying annie's v2 patch
>>   - applying your patch
>> as dom0 and using a 3.14-rc5 as domU kernel.
>> 
>> Unfortunately i'm still getting the Bad grant references ..
>> 

> :-( That's bad news.

> I guess you always have the same DomU kernel when testing? That means we
> can narrow down the bug to netback only.

Yes my previous tests (from my previous mail):

- First testing a baseline that worked o.k. for several days (3.13.6 for both 
dom0 and domU)
- Testing domU 3.14-rc5 and dom0 3.13.6, this worked ok.
- Testing dom0 3.14-rc5 and domU 3.13.6, this failed.
- After that took 3.13.6 as base and first applied all the general xen related 
patches for the dom0 kernel, that works ok.
- After that started to apply the netback changes for 3.14 and that failed 
after the commit "ca2f09f2b2c6c25047cfc545d057c4edfcfe561c xen-netback: improve 
guest-receive-side flow control".

Also seem to indicate just that, although it could also be something in this 
netback commit that triggers a latent bug in netfront, can't rule that one out 
completly.

But the trigger is in that commit &&
annie's and your patch seem to have no effect at all( on this issue) &&
later commits in 3.14 do seems to mask it / make it less likely to trigger, but 
do not fix it.

> Paul, do you have any idea what might go wrong?

> Wei.



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