[PATCH 2/2] [fs] proc/vmcore: check the dummy place holder for offline cpu to avoid warning

[Xunlei Pang]

On 12/14/2016 at 02:11 PM, Pingfan Liu wrote:
> kexec-tools always allocates program headers for possible cpus. But
> when crashing, offline cpus have dummy headers. We do not copy these
> dummy notes into ELF file, also have no need of warning on them.
>
> Signed-off-by: Pingfan Liu <piliu at redhat.com>
> ---
>  fs/proc/vmcore.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 8ab782d..bbc9dad 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -526,9 +526,10 @@ static u64 __init get_vmcore_size(size_t elfsz, size_t elfnotesegsz,
>   */
>  static int __init update_note_header_size_elf64(const Elf64_Ehdr *ehdr_ptr)
>  {
> -	int i, rc=0;
> +	int i, j, rc = 0;
>  	Elf64_Phdr *phdr_ptr;
>  	Elf64_Nhdr *nhdr_ptr;
> +	bool warn;
>  
>  	phdr_ptr = (Elf64_Phdr *)(ehdr_ptr + 1);
>  	for (i = 0; i < ehdr_ptr->e_phnum; i++, phdr_ptr++) {
> @@ -536,6 +537,7 @@ static int __init update_note_header_size_elf64(const Elf64_Ehdr *ehdr_ptr)
>  		u64 offset, max_sz, sz, real_sz = 0;
>  		if (phdr_ptr->p_type != PT_NOTE)
>  			continue;
> +		warn = true;
>  		max_sz = phdr_ptr->p_memsz;
>  		offset = phdr_ptr->p_offset;
>  		notes_section = kmalloc(max_sz, GFP_KERNEL);
> @@ -547,7 +549,7 @@ static int __init update_note_header_size_elf64(const Elf64_Ehdr *ehdr_ptr)
>  			return rc;
>  		}
>  		nhdr_ptr = notes_section;
> -		while (nhdr_ptr->n_namesz != 0) {
> +		for (j = 0; nhdr_ptr->n_namesz != 0; j++) {

Hi Pingfan,

I think we don't need to be this complex, how about simply check before while loop,
if it is the cpu dummy note(initialize it with some magic), then handle it differently,
e.g. set a "nowarn" flag to use afterwards and make sure it has zero p_memsz?

Also do the similar thing for update_note_header_size_elf32()?

Regards,
Xunlei

>  			sz = sizeof(Elf64_Nhdr) +
>  				(((u64)nhdr_ptr->n_namesz + 3) & ~3) +
>  				(((u64)nhdr_ptr->n_descsz + 3) & ~3);
> @@ -559,11 +561,22 @@ static int __init update_note_header_size_elf64(const Elf64_Ehdr *ehdr_ptr)
>  			real_sz += sz;
>  			nhdr_ptr = (Elf64_Nhdr*)((char*)nhdr_ptr + sz);
>  		}
> +		if (real_sz != 0)
> +			warn = false;
> +		if (j == 1) {
> +			nhdr_ptr = notes_section;
> +			if ((nhdr_ptr->n_type == NT_DUMMY)
> +			  && !strncmp(KEXEC_CORE_NOTE_NAME,
> +				(char *)nhdr_ptr + sizeof(Elf64_Nhdr),
> +				strlen(KEXEC_CORE_NOTE_NAME))) {
> +				/* do not copy this dummy note */
> +				real_sz = 0;
> +			}
> +		}
>  		kfree(notes_section);
>  		phdr_ptr->p_memsz = real_sz;
> -		if (real_sz == 0) {
> +		if (warn)
>  			pr_warn("Warning: Zero PT_NOTE entries found\n");
> -		}
>  	}
>  
>  	return 0;