[PATCH] makedumpfile: call initial before use cache

[HAGIO KAZUHITO(萩尾 一仁)]

Hi Lichen,

sorry for the long delay.

On 2024/06/25 10:57, Lichen Liu wrote:
> Run 'makedumpfile --mem-usage /proc/kcore' will coredump on ppc64, it is
> because show_mem_usage()->get_page_offset()->get_versiondep_info_ppc64()
> ->readmem() use cache before it is inited by initial().
> 
> Currently only ppc64 has this issue because only
> get_versiondep_info_ppc64() call readmem().
> 
> Signed-off-by: Lichen Liu <lichliu at redhat.com>
> ---
>   makedumpfile.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/makedumpfile.c b/makedumpfile.c
> index 5b34712..6a42264 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -12019,6 +12019,9 @@ int show_mem_usage(void)
>   		DEBUG_MSG("Read vmcoreinfo from NOTE segment: %d\n", vmcoreinfo);
>   	}
>   
> +	if (!initial())
> +		return FALSE;
> +
>   	if (!get_page_offset())
>   		return FALSE;
>   
> @@ -12034,9 +12037,6 @@ int show_mem_usage(void)
>   			return FALSE;
>   	}
>   
> -	if (!initial())
> -		return FALSE;
> -
>   	if (!open_dump_bitmap())
>   		return FALSE;
>   

initial() needs to be called after set_kcore_vmcoreinfo(), when there is 
no vmcoreinfo in /proc/kcore ELF note.

So with the patch, "makedumpfile --mem-usage" fails on kernels that do 
not have a vmcoreinfo in ELF note, e.g. RHEL7 kernel:

   # makedumpfile-dev -f --mem-usage /proc/kcore
   exclude_free_page: Can't get necessary symbols for excluding free pages.

   makedumpfile Failed.


Probably readmem() should not be called before initial() in the first 
place.  I think it's the root cause, but I'm not sure how we can fix it.

A workaround I thought of is that moving get_page_offset() and 
get_phys_base() into the !vmcoreinfo block.  These are needed by 
set_kcore_vmcoreinfo(), so we can avoid calling them if there is a 
vmcoreinfo in ELF note:

--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -12019,14 +12019,14 @@ int show_mem_usage(void)
                 DEBUG_MSG("Read vmcoreinfo from NOTE segment: %d\n", 
vmcoreinfo);
         }

-       if (!get_page_offset())
-               return FALSE;
+       if (!vmcoreinfo) {
+               if (!get_page_offset())
+                       return FALSE;

-       /* paddr_to_vaddr() on arm64 needs phys_base. */
-       if (!get_phys_base())
-               return FALSE;
+               /* paddr_to_vaddr() on arm64 needs phys_base. */
+               if (!get_phys_base())
+                       return FALSE;

-       if (!vmcoreinfo) {
                 if (!get_sys_kernel_vmcoreinfo(&vmcoreinfo_addr, 
&vmcoreinfo_len))
                         return FALSE;


This will work only for 4.19 and later kernels, but might reduce users 
that hit the issue.  Does this work for you?

Thanks,
Kazu