[Crash-utility] crash: cannot resolve "init_task_union"

[Dave Anderson]

Dave Anderson wrote:

>
> Sachin,
>
> This may require help from the IBM ppc64 people out there,
> but it appears that the issue at hand has something to do
> with the uniprocessor aspect.
>
> Your vmlinux is an SMP kernel, but I'm guessing that the wrong
> choice of "runq" addresses is being made below:
>
>         if (symbol_exists("per_cpu__runqueues") &&
>             VALID_MEMBER(runqueue_idle)) {
>                 runqbuf = GETBUF(SIZE(runqueue));
>                 for (i = 0; i < nr_cpus; i++) {
>                        if ((kt->flags & SMP) && (kt->flags & PER_CPU_OFF)) {
>                                 runq = symbol_value("per_cpu__runqueues") +
>                                         kt->__per_cpu_offset[i];
>                         } else
>                                 runq = symbol_value("per_cpu__runqueues");
>
>                         readmem(runq, KVADDR, runqbuf,
>                                 SIZE(runqueue), "runqueues entry (per_cpu)",
>                                 FAULT_ON_ERROR);
>                         tasklist[i] = ULONG(runqbuf + OFFSET(runqueue_idle));
>                         if (IS_KVADDR(tasklist[i]))
>                                 cnt++;
>
> I don't know what your "kt->flags" is showing at the
> decision point above, but if you hack the code and force
> it to select the "other" runq value, does it work OK?
>
> When CONFIG_SMP is not configured into the kernel, then
> the direct value of "per_cpu__runqueues" is used, whereas
> with SMP kernels, the appropriate offset needs to be
> applied.  At least that's how it works (has worked?) with
> the other architectures.
>
> Dave

Looking at ppc64_paca_init(), it appears that this might be
the problem if SMP is not set in kt->flags:

static void
ppc64_paca_init()
{
        ...

        for (i = cpus = 0; i < nr_paca; i++) {
                div_t val = div(i, BITS_FOR_LONG);
                /*
                 * CPU online?
                 */
                if (!(cpu_online_map[val.quot] & (0x1UL << val.rem)))
                        continue;

                readmem(symbol_value("paca") + (i * SIZE(ppc64_paca)),
                        KVADDR, cpu_paca_buf, SIZE(ppc64_paca),
                        "paca entry", FAULT_ON_ERROR);

                kt->__per_cpu_offset[i] = ULONG(cpu_paca_buf + data_offset);
                kt->flags |= PER_CPU_OFF;
                cpus++;
        }
        kt->cpus = cpus;
        if (kt->cpus > 1)
                kt->flags |= SMP;
}

If SMP is not set coming into this function, and therefore won't
get set above, then the wrong runq pointer would be selected later
on get_idle_threads().

Dave

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