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

[Liu ping fan]

On Thu, Dec 15, 2016 at 7:56 AM, Xunlei Pang  wrote:
> 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 
>> ---
>>  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?
>
I had thought that how the percpu note section was filled. But you are
right,  we can suppose that for all archs, cpus just overwrite the
note, not append the note.

> Also do the similar thing for update_note_header_size_elf32()?
>
Yes, will fix it.

Thx,

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Re: [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 
> ---
>  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;


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

[Pingfan Liu]

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 
---
 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++) {
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;
-- 
2.7.4


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