Re: [Xen-devel] [PATCH 7/7] xl: Fix 'free_memory' to include outstanding_claims value.

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Jackson writes ("Re: [PATCH 7/7] xl: Fix 'free_memory' to include 
outstanding_claims value."):
> Konrad Rzeszutek Wilk writes ("[PATCH 7/7] xl: Fix 'free_memory' to include 
> outstanding_claims value."):
> > Updating to make it clear that free_memory reported by 'xl info'
> > is influenced by the outstanding claim value. [...]
> 
> >      if (libxl_get_physinfo(ctx, &info) != 0) {
> >          fprintf(stderr, "libxl_physinfo failed.\n");
> >          return;
> >      }
> > -
> > +    /*
> > +     * Don't bother checking "claim_mode" as user might have turned it off
> > +     * and we have outstanding claims.
> > +     */
> > +    if ((claims = libxl_get_claiminfo(ctx)) < 0){
> > +        fprintf(stderr, "libxl_get_claiminfo failed. errno: %d (%s)\n",
> > +                errno, strerror(errno));
> > +        return;
> > +    }
> ...
> > +        printf("free_memory            : %"PRIu64"\n", (info.free_pages - 
> > claims) / i);
> 
> This has a race, I think.

I have checked this and the race is in the hypercall API.  The
hypercall API has already been checked in.  So, under the
circumstances, for this patch:

Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>


However, there is a release-critical bug here.  The following things
need to be changed:

 * We need a race-free version of the hypercall API.
 * We need a race-free version of the xc API.
 * We need a race-free version of the libxl API.

I think this is a release-critical bug because fixing it involves an
API change at all these 3 levels.  We don't want to release 4.3 with
a broken API as that will complicate fixing this bug.

George, can you please add this to your tracking list ?

Having said all that, George, am I OK from a freeze POV to pull
Konrad's series into staging ?

Ian.

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