[Crash-utility] crash version 4.0-3.15 is available

[Dave Anderson]

Dave Anderson wrote:

> Itsuro ODA wrote:
>
> > Hi Dave,
> >
> > > - Introduced support for xendumps of para-virtualized ia64 kernels.
> > >   It should be noted that currently the ia64 Xen kernel does not
> > >   lay down a switch_stack for the panic task, so only raw "bt -t"
> > >   backtraces can be done on the panic task.  (anderson at redhat.com)
> >
> > page_index may contain INVALID_MFN (0xffffffffffffffffUL).
> > I think it is better to check it.
> > Here is a patch for this.
> >
> > ---
> > --- crash-4.0-3.15-org/xendump.h        2006-12-21 09:57:29.000000000 +0900
> > +++ crash-4.0-3.15/xendump.h    2006-12-21 14:37:35.000000000 +0900
> > @@ -113,3 +113,8 @@
> >      uint32_t hypercall_imm; /* Break imm for Xen hypercalls.  */
> >  /* #endif */
> >  } xen_domctl_arch_setup_t;
> > +
> > +#ifdef IA64
> > +#define INVALID_MFN (0xffffffffffffffffUL)
> > +#endif
> > +
> > --- crash-4.0-3.15-org/xendump.c        2006-12-21 09:57:29.000000000 +0900
> > +++ crash-4.0-3.15/xendump.c    2006-12-21 14:42:48.000000000 +0900
> > @@ -31,6 +31,7 @@
> >
> >  static void xc_core_p2m_create(void);
> >  static ulong xc_core_pfn_to_page_index(ulong);
> > +static int check_mfn_is_valid(ulong);
> >
> >  /*
> >   *  Determine whether a file is a xendump creation, and if TRUE,
> > @@ -1362,7 +1363,7 @@
> >         off_t offset;
> >
> >         if (xd->flags & XC_CORE_NO_P2MM)
> > -               return pfn;
> > +               return check_mfn_is_valid(pfn) ? pfn : PFN_NOT_FOUND;
> >
> >         idx = pfn/PFNS_PER_PAGE;
> >
> > @@ -1405,6 +1406,34 @@
> >         return mfn_idx;
> >  }
> >
> > +static int
> > +check_mfn_is_valid(ulong idx)
> > +{
> > +        ulong mfn;
> > +
> > +       if (idx >= xd->xc_core.header.xch_nr_pages)
> > +               return FALSE;
> > +
> > +        if (lseek(xd->xfd,
> > +           (off_t)xd->xc_core.header.xch_index_offset + idx * sizeof(ulong),
> > +            SEEK_SET) == -1) {
> > +                error(INFO, "cannot lseek to page index\n");
> > +                return FALSE;
> > +        }
> > +
> > +       if (read(xd->xfd, &mfn, sizeof(ulong)) != sizeof(ulong)) {
> > +               error(INFO, "cannot read index page %d\n", idx);
> > +               return FALSE;
> > +       }
> > +
> > +       if (mfn == INVALID_MFN) {
> > +               error(INFO, "idx: %lx indicates INVALID_MFN\n", idx);
> > +               return FALSE;
> > +       } else {
> > +               return TRUE;
> > +       }
> > +}
> > +
> >  /*
> >   *  Store the panic task's stack hooks from where it was found
> >   *  in get_active_set_panic_task().
> > ---
> >
> > Thanks.
> > --
> > Itsuro ODA <oda at valinux.co.jp>
>
> Oda-san,
>
> Good catch.  I was never reading "bad addresses", so I didn't
> see any issue there.  Now, after going back and checking it out,
> I see that if you attempt to read an uninstantiated pfn, it returns
> the page index, and so it seeks to and reads whatever's in the
> xendump from that location.  Given the way the FV xendump is
> laid out, there has to be *something* there in the dumpfile, which
> I would have thought would have been sparse file space and
> read as all zeroes?  But in some dumps, it looks like there's "junk"
> data there?  Whatever -- it's harmless.
>
> In any case, I agree with you -- it's much better to return a read
> error as xc_core_read() expects.  I'll just adjust your patch slightly
> to handle all architectures.
>
> Thanks,
>   Dave

Oda-san,

Thanks again for the "overnight-QA" and for introducing support
for xendumps of fully-virtualized ia64 kernels!  I've posted a new
crash version with both fixes.

I modified your check_mfn_is_valid() function so that it could
be used by all 3 architectures as well as for xendumps of
32-bit kernels running on a 64-bit host:


/*
 *  In xendumps containing INVALID_MFN markers in the page index,
 *  return the validity of the pfn.
 */
static int
xc_core_pfn_valid(ulong pfn)
{
        ulong mfn;
        off_t offset;

        if (pfn >= (ulong)xd->xc_core.header.xch_nr_pages)
                return FALSE;

        offset = (off_t)xd->xc_core.header.xch_index_offset;

        if (xd->flags & XC_CORE_64BIT_HOST)
                offset += (off_t)(pfn * sizeof(ulonglong));
        else
                offset += (off_t)(pfn * sizeof(ulong));

        /*
         *  The lseek and read should never fail, so report
         *  any errors unconditionally.
         */
        if (lseek(xd->xfd, offset, SEEK_SET) == -1) {
                error(INFO,
                    "xendump: cannot lseek to page index for pfn %lx\n",
                        pfn);
                return FALSE;
        }

        if (read(xd->xfd, &mfn, sizeof(ulong)) != sizeof(ulong)) {
                error(INFO,
                    "xendump: cannot read index page for pfn %lx\n",
                        pfn);
                return FALSE;
        }

        /*
         *  If it's an invalid mfn, let the caller decide whether
         *  to display an error message (unless debugging).
         */
        if (mfn == INVALID_MFN) {
                if (CRASHDEBUG(1))
                        error(INFO,
                            "xendump: pfn %lx contains INVALID_MFN\n",
                                pfn);
                return FALSE;
        }

        return TRUE;
}

Thanks again,
  Dave

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