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

[Dave Anderson]

Dave Anderson wrote:

> 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

And then there's this code in kernel_init():

        if ((sp1 = symbol_search("__per_cpu_start")) &&
            (sp2 =  symbol_search("__per_cpu_end")) &&
            (sp1->type == 'A') && (sp2->type == 'A') &&
            (sp2->value > sp1->value))
                kt->flags |= SMP|PER_CPU_OFF;

On a RHEL5 x86_64:

  crash> sym -q __per_cpu_ | grep -e start -e end
  ffffffff80603000 (A) __per_cpu_start
  ffffffff80607288 (A) __per_cpu_end
  crash>

On a RHEL5 x86:

  crash> sym -q __per_cpu | grep -e start -e end
  c03100a0 (A) __per_cpu_start
  c0315ae4 (A) __per_cpu_end
  crash>

But on your RHEL5 ppc64 kernel:

  # nm -Bn vmlinux | grep __per_cpu
  c000000000430100 D __per_cpu_start
  c0000000004356f0 D __per_cpu_end
  #

So if you remove the two "type == 'A'" qualifiers
from the if statement above, does it work OK?

Dave




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