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

[Liu ping fan]

On Wed, Dec 14, 2016 at 2:11 PM, Pingfan Liu <piliu at redhat.com> wrote:
> kexec-tools always allocates program headers for each possible cpu. This

The code is in the file:    kexec-tools/kexec/crashdump-elf.c
   nr_cpus = sysconf(_SC_NPROCESSORS_CONF);

> 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.
>
> 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
>