Re: [Xen-devel] [BUG] kernel bug encountered at drivers/net/xen-netback/netback.c:430!

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Christoph Moench-Tegeder [mailto:cmt@xxxxxxxxxxxxxx]
> Sent: 03 January 2018 20:34
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: 'Alex Braunegg' <alex.braunegg@xxxxxxxxx>; 'Michael Collins'
> <mike@xxxxxxxxxxx>; 'Juergen Gross' <jgross@xxxxxxxx>; xen-
> devel@xxxxxxxxxxxxxxxxxxxx; Wei Liu <wei.liu2@xxxxxxxxxx>
> Subject: Re: [Xen-devel] [BUG] kernel bug encountered at drivers/net/xen-
> netback/netback.c:430!
> 
> ## Paul Durrant (Paul.Durrant@xxxxxxxxxx):
> 
> > How easy is it to trigger this? I'm assuming, from the original
> > description, that I can probably trigger it by forcibly terminating
> > a running domain and then trying to restart it.
> 
> As Alex said: in the "common cases" (like his and mine) it seems to
> be enough to run a few DomUs and just wait a little (no special
> load required) - with my 10 domains, the bg triggers in a few minutes
> ( https://lists.xenproject.org/archives/html/xen-devel/2017-
> 12/msg01516.html
> is my report of the issue - I didn't spot Alex' report).
> The order of event here is:
> - boot Dom0
> - xl create a few DomUs (all recent Linux, all builder=hvm in my setup,
>   each VM has exactly one virtual network interface, all bridged onto
>   the one ethernet interface on the Dom0 which carries all traffic
>   to the Dom0 and the DomUs)
> - after a few minutes, the Dom0 kernel logs the BUG() in question
> - shortly after (not immediately! - may take even some more minutes)
>   the DomU behind the vif reported in the BUG becomes unresponsive:
>   no network traffic, no reaction on the virtual console, no message
>   in syslog).
> - trying to xl destroy the unresponsive domain (or trying to do a
>   normal shutdown on one of the other domains) results in the corrupted
>   state documented in my earlier report (see link).
> 
> In my case this "cannot" be an issue with an old gcc - Debian 9 ships
> with "gcc (Debian 6.3.0-18) 6.3.0 20170516" (but beware of new bugs,
> who knows?).
> 
> I could try a new kernel (KPTI, yay!) with that "mildly suspicious" commit
> cc8737a5fe9051b7fa052b08c57ddb9f539c389a reverted on the weekend and
> report back (just to rule that out - like you, I don't really believe
> that this is the cause).
> For the record, I'm still running 4.13.16 on the Dom0 (that's the last
> working Dom0 kernel).

Thanks. Well, that's the only netback commit that's in master but not in 
4.13.16 so it would be useful to conclusively rule that out as a cause.

  Cheers,

    Paul

> 
> Regards,
> Christoph
> 
> --
> Spare Space
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