Re: [PATCH] xend: make xc.vcpu_getinfo() return None if guest not existed

[Matt Wilson <msw@linux.com>]

On Tue, Dec 03, 2013 at 06:38:10PM +0800, Joe Jin wrote:
> Hi Matt,
> 
> Can you please review the patch? or any other ideas to fix the race?

Hi Joe,

I'm sorry about the delay. As you can imagine, it's a busy time of
year for us at work.

When I commented on the original patch, I was talking about the type
of exception you were catching. I prefer the approach in the original
patch to this one, with one change:

The RuntimeError class isn't guaranteed to have exception arguments
that include an errno value. The xen.lowlevel.xc.Error class is always
set via PyErr_SetFromErrno(). So instead of

    except RuntimeError, exn:

I'd rather see:

    except xen.lowlevel.xc.Error, exn:

You can import xen.lowlevel.xc.Error to the local namespace by adding
something like:

from xen.lowlevel.xc import xc, Error as XenError
...
except XenError, exn:

Does that make sense?

--msw

> On 11/21/13 11:12, Joe Jin wrote:
> > We hit failure when when reboot some guests at the same time,
> > xend.log has below:
> > [2013-09-04 20:01:26 6254] ERROR (XendDomainInfo:496) VM start failed
> > Traceback (most recent call last):
> >   File "/usr/lib64/python2.4/site-packages/xen/xend/XendDomainInfo.py", line 482, in start
> >     XendTask.log_progress(31, 60, self._initDomain)
> >   File "/usr/lib64/python2.4/site-packages/xen/xend/XendTask.py", line 209, in log_progress
> >     retval = func(*args, **kwds)
> >   File "/usr/lib64/python2.4/site-packages/xen/xend/XendDomainInfo.py", line 2918, in _initDomain
> >     node = self._setCPUAffinity()
> >   File "/usr/lib64/python2.4/site-packages/xen/xend/XendDomainInfo.py", line 2835, in _setCPUAffinity
> >     best_node = find_relaxed_node(candidate_node_list)[0]
> >   File "/usr/lib64/python2.4/site-packages/xen/xend/XendDomainInfo.py", line 2803, in find_relaxed_node
> >     cpuinfo = dom.getVCPUInfo()
> >   File "/usr/lib64/python2.4/site-packages/xen/xend/XendDomainInfo.py", line 1600, in getVCPUInfo
> >     raise XendError(str(exn))
> > XendError: (3, 'No such process')
> > 
> > This caused by one or more guests be rebooted between the call of
> > find_relaxed_node()->list('all') and getVCPUInfo(). This patch will let
> > xc.vcpu_getinfo() return None if guest not existed to avoid the failure.
> > 
> > Signed-off-by: Joe Jin <joe.jin@oracle.com>
> > Cc: Matt Wilson <msw@amazon.com>
> > Cc: Keir Fraser <keir@xen.org>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > Cc: Ian Jackson <ian.jackson@eu.citrix.com>
> > Cc: Ian Campbell <ian.campbell@citrix.com>
> > Cc: Roger Pau Monne <roger.pau@citrix.com>
> > ---
> >  tools/python/xen/lowlevel/xc/xc.c       |   15 ++++++++++++---
> >  tools/python/xen/xend/XendDomainInfo.py |    2 +-
> >  2 files changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/tools/python/xen/lowlevel/xc/xc.c b/tools/python/xen/lowlevel/xc/xc.c
> > index 2625fc4..9a7e589 100644
> > --- a/tools/python/xen/lowlevel/xc/xc.c
> > +++ b/tools/python/xen/lowlevel/xc/xc.c
> > @@ -396,8 +396,13 @@ static PyObject *pyxc_vcpu_getinfo(XcObject *self,
> >          return pyxc_error_to_exception(self->xc_handle);
> >  
> >      rc = xc_vcpu_getinfo(self->xc_handle, dom, vcpu, &info);
> > -    if ( rc < 0 )
> > -        return pyxc_error_to_exception(self->xc_handle);
> > +    if ( rc < 0)
> > +    {
> > +        if (errno == ESRCH)
> > +            return Py_BuildValue("");
> > +        else
> > +            return pyxc_error_to_exception(self->xc_handle);
> > +    }
> >  
> >      cpumap = xc_cpumap_alloc(self->xc_handle);
> >      if(cpumap == NULL)
> > @@ -407,7 +412,11 @@ static PyObject *pyxc_vcpu_getinfo(XcObject *self,
> >      if ( rc < 0 )
> >      {
> >          free(cpumap);
> > -        return pyxc_error_to_exception(self->xc_handle);
> > +
> > +        if (errno == ESRCH)
> > +            return Py_BuildValue("");
> > +        else
> > +            return pyxc_error_to_exception(self->xc_handle);
> >      }
> >  
> >      info_dict = Py_BuildValue("{s:i,s:i,s:i,s:L,s:i}",
> > diff --git a/tools/python/xen/xend/XendDomainInfo.py b/tools/python/xen/xend/XendDomainInfo.py
> > index e9d3e7e..6b5fd83 100644
> > --- a/tools/python/xen/xend/XendDomainInfo.py
> > +++ b/tools/python/xen/xend/XendDomainInfo.py
> > @@ -1518,7 +1518,7 @@ class XendDomainInfo:
> >              for i in range(0, self.info['VCPUs_max']):
> >                  if self.domid is not None:
> >                      info = xc.vcpu_getinfo(self.domid, i)
> > -
> > +                    if info == None: continue
> >                      sxpr.append(['vcpu',
> >                                   ['number',   i],
> >                                   ['online',   info['online']],
> > 
> 
>