[PATCH 1/2] kexec: add a dummy note for each offline cpu

[Liu ping fan]

On Thu, Dec 15, 2016 at 3:16 PM, Dave Young <dyoung at redhat.com> wrote:
> Hi, Pingfan
> On 12/14/16 at 02:11pm, Pingfan Liu wrote:
>> kexec-tools always allocates program headers for each possible cpu. This
>> incurs zero PT_NOTE for offline cpu. We mark this case so that later,
>> the capture kernel can distinguish it from the mistake of allocated
>> program header.
>> The counterpart of the capture kernel comes in next patch.
>
> I thought you saw the warnings on ppc64 and it might be a ppc64 issue.
It affects all archs, since kexec-tools creates each program header
for each _present_ cpu. So if the cpu is offline, then the warning
buzzes.

> But if this is instead a general issue, can we think about if this is
> really necessary?
>
> Does it have any side effect other than the warning messages? If there
> is nothing bad other than the warnings maybe leave it as is will be
> a better way.
>
I think kernel warning always made people upset  who do not know the
back ground of the related field.
While on the other hand, the program behaves correctly against our
expectation, so just suppress the warning to make everyone easy.

Regards,
Pingfan
>>
>> Signed-off-by: Pingfan Liu <piliu at redhat.com>
>> ---
>> This unnecessary warning buzz on all archs when there is offline cpu
>>
>>  include/uapi/linux/elf.h | 1 +
>>  kernel/kexec_core.c      | 9 +++++++++
>>  2 files changed, 10 insertions(+)
>>
>> diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
>> index b59ee07..9744f1e 100644
>> --- a/include/uapi/linux/elf.h
>> +++ b/include/uapi/linux/elf.h
>> @@ -367,6 +367,7 @@ typedef struct elf64_shdr {
>>   * using the corresponding note types via the PTRACE_GETREGSET and
>>   * PTRACE_SETREGSET requests.
>>   */
>> +#define NT_DUMMY     0
>>  #define NT_PRSTATUS  1
>>  #define NT_PRFPREG   2
>>  #define NT_PRPSINFO  3
>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>> index 5616755..aeac16e 100644
>> --- a/kernel/kexec_core.c
>> +++ b/kernel/kexec_core.c
>> @@ -891,9 +891,12 @@ void __crash_kexec(struct pt_regs *regs)
>>       if (mutex_trylock(&kexec_mutex)) {
>>               if (kexec_crash_image) {
>>                       struct pt_regs fixed_regs;
>> +                     unsigned int cpu;
>>
>>                       crash_setup_regs(&fixed_regs, regs);
>>                       crash_save_vmcoreinfo();
>> +                     for_each_cpu_not(cpu, cpu_online_mask)
>> +                             crash_save_cpu(NULL, cpu);
>>                       machine_crash_shutdown(&fixed_regs);
>>                       machine_kexec(kexec_crash_image);
>>               }
>> @@ -1040,6 +1043,12 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
>>       buf = (u32 *)per_cpu_ptr(crash_notes, cpu);
>>       if (!buf)
>>               return;
>> +     if (regs == NULL) {
>> +             buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_DUMMY,
>> +                             NULL, 0);
>> +             final_note(buf);
>> +             return;
>> +     }
>>       memset(&prstatus, 0, sizeof(prstatus));
>>       prstatus.pr_pid = current->pid;
>>       elf_core_copy_kernel_regs(&prstatus.pr_reg, regs);
>> --
>> 2.7.4
>>
>
> Thanks
> Dave