Re: [PATCH] xl create: endless loop

[Christoph Egger <Christoph.Egger@amd.com>]

On Monday 08 November 2010 09:18:19 Zhang, Yang Z wrote:
> Did the patch apply? This issue still exist in xen-unstable(22364).

Yes.

>
> best regards
> yang
>
> > -----Original Message-----
> > From: xen-devel-bounces@lists.xensource.com
> > [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Christoph
> > Egger Sent: Thursday, November 04, 2010 11:40 PM
> > To: xen-devel@lists.xensource.com
> > Cc: Jackson; Stefano Stabellini
> > Subject: Re: [Xen-devel][PATCH] xl create: endless loop
> >
> > On Wednesday 03 November 2010 17:12:47 Christoph Egger wrote:
> > > On Thursday 21 October 2010 16:11:55 Stefano Stabellini wrote:
> > > > On Tue, 19 Oct 2010, Christoph Egger wrote:
> > > > > On Monday 18 October 2010 14:50:35 Christoph Egger wrote:
> > > > > > Hi!
> > > > > >
> > > > > > I cannot start a guest with 'xl create' due to an endless loop
> > > > > > in libxl.c, function libxl__get_free_memory_slack():
> > > > > >
> > > > > > There is this code snippet:
> > > > > >
> > > > > > retry:
> > > > > >     free_mem_slack_s = libxl__xs_read(gc, XBT_NULL,
> > > > > > free_mem_slack_path); if (!free_mem_slack_s) {
> > > > > >         rc = libxl__fill_dom0_memory_info(gc, &target_memkb);
> > > > > >         if (rc < 0)
> > > > > >             return rc;
> > > > > >         goto retry;
> > > > > >     } else {
> > > > > >
> > > > > >
> > > > > > libxl__xs_read() returns 0 and libxl__fill_dom0_memory_info()
> > > > > > also returns 0. So there's a loop of retries.
> > > > >
> > > > > Attached patch fixes the endless loop.
> > > > >
> > > > > Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>
> > > >
> > > > thanks for the patch but this cannot possibly be the right fix:
> > > >
> > > >
> > > > diff -r 9d8d6b93114e tools/libxl/libxl.c
> > > > --- a/tools/libxl/libxl.c	Mon Oct 18 15:24:39 2010 +0200
> > > > +++ b/tools/libxl/libxl.c	Tue Oct 19 10:29:00 2010 +0200
> > > > @@ -2836,7 +2836,7 @@ retry:
> > > >      free_mem_slack_s = libxl__xs_read(gc, XBT_NULL,
> > > > free_mem_slack_path); if (!free_mem_slack_s) {
> > > >          rc = libxl__fill_dom0_memory_info(gc, &target_memkb);
> > > > -        if (rc < 0)
> > > > +        if (rc <= 0)
> > > >              return rc;
> > > >          goto retry;
> > > >      } else {
> > > >
> > > > the idea is that libxl__fill_dom0_memory_info should fill the
> > > > missing informations in xenstore so that we can go ahead and try to
> > > > read them again and the second time should be successful.
> > > > Libxl__fill_dom0_memory_info returns 0 on success, so it is correct
> > > > to goto retry in that case.
> > > >
> > > > The bug must be in libxl__fill_dom0_memory_info that doesn't return
> > > > error when it should.
> > > > Does the appended patch works for you?
> > > >
> > > > ---
> > > >
> > > > diff -r 00b92112b055 tools/libxl/libxl.c
> > > > --- a/tools/libxl/libxl.c	Wed Oct 20 17:26:51 2010 +0100
> > > > +++ b/tools/libxl/libxl.c	Thu Oct 21 15:08:29 2010 +0100
> > > > @@ -2793,11 +2793,11 @@ retry_transaction:
> > > >
> > > >      rc = libxl_domain_info(ctx, &info, 0);
> > > >      if (rc < 0)
> > > > -        return rc;
> > > > +        goto out;
> > > >
> > > >      rc = libxl_get_physinfo(ctx, &physinfo);
> > > >      if (rc < 0)
> > > > -        return rc;
> > > > +        goto out;
> > > >
> > > >      libxl__xs_write(gc, t, target_path, "%"PRIu32,
> > > >              (uint32_t) info.current_memkb); @@ -2816,9 +2816,12
> >
> > @@
> >
> > > > retry_transaction:
> > > >      rc = 0;
> > > >
> > > >  out:
> > > > -    if (!xs_transaction_end(ctx->xsh, t, 0))
> > > > +    if (!xs_transaction_end(ctx->xsh, t, 0)) {
> > > >          if (errno == EAGAIN)
> > > >              goto retry_transaction;
> > > > +        else
> > > > +            rc = ERROR_FAIL;
> > > > +    }
> > > >
> > > >
> > > >      return rc;
> > >
> > > No, this patch has no effect for me.
> > > In libxl__fill_dom0_memory_info(), the code path goes that way:
> > >
> > >     t = xs_transaction_start(ctx->xsh);
> > >
> > >     target = libxl__xs_read(gc, t, target_path);
> > >     if (target) {    <-- target contains "5"
> > >         *target_memkb = strtoul(target, &endptr, 10);
> > >         if (*endptr != '\0') {     <-- *endptr contains '\0'
> > >             LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,
> > >                     "invalid memory target %s from %s\n", target,
> > > target_path);
> > >             rc = ERROR_FAIL;
> > >             goto out;
> > >         }
> > >         rc = 0;
> > >         goto out;    <-- take this jump with rc being 0
> > >     }
> >
> > A slightly modified version works.
> >
> > Signed-off-by: Mark Langsdorf <Mark.Langsdorf@amd.com>
> > Signed-off-by: Christoph Egger <Christoph.Egger@amd.com>


-- 
---to satisfy European Law for business letters:
Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach b. Muenchen
Geschaeftsfuehrer: Alberto Bozzo, Andrew Bowd
Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen
Registergericht Muenchen, HRB Nr. 43632