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

[Baoquan He <bhe@redhat.com>]

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.

When you execute dmesg on your testing machine and grep nr_cpu_ids,
what's the value of nr_cpu_ids?

> 
> Signed-off-by: Pingfan Liu <piliu@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
> 

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