[1/2] vmcore: allow alternate dump capturing methods to export vmcore without is_kdump_kernel()

Currently, is_kdump_kernel() returns true when elfcorehdr_addr is set.
While elfcorehdr_addr is set for kexec based kernel dump mechanism,
alternate dump capturing methods like fadump [1] also set it to export
the vmcore. is_kdump_kernel() is used to restrict resources in crash
dump capture kernel but such restrictions may not be desirable for
fadump. Allow is_kdump_kernel() to be defined differently for such
scenarios. With this, is_kdump_kernel() could be false while vmcore
is usable. So, introduce is_crashdump_kernel() to return true when
elfcorehdr_addr is set and use it for vmcore related checks.

[1] https://docs.kernel.org/powerpc/firmware-assisted-dump.html

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
---
 include/linux/crash_dump.h | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

Hi Hari,

On 09/02/23 at 12:34am, Hari Bathini wrote:
> Currently, is_kdump_kernel() returns true when elfcorehdr_addr is set.
> While elfcorehdr_addr is set for kexec based kernel dump mechanism,
> alternate dump capturing methods like fadump [1] also set it to export
> the vmcore. is_kdump_kernel() is used to restrict resources in crash
> dump capture kernel but such restrictions may not be desirable for
> fadump. Allow is_kdump_kernel() to be defined differently for such
> scenarios. With this, is_kdump_kernel() could be false while vmcore
> is usable. So, introduce is_crashdump_kernel() to return true when
> elfcorehdr_addr is set and use it for vmcore related checks.

I got what is done in these two patches, but didn't get why they need be
done. vmcore_unusable()/is_vmcore_usable() are only unitilized in ia64.
Why do you care if it's is_crashdump_kernel() or is_kdump_kernel()?
If you want to override the generic is_kdump_kernel() with powerpc's own
is_kdump_kernel(), your below change is enough to allow you to do that.
I can't see why is_crashdump_kernel() is needed. Could you explain that
specifically?

#ifndef is_kdump_kernel
static inline bool is_kdump_kernel(void)
{
        return elfcorehdr_addr != ELFCORE_ADDR_MAX;
}
#endif

Thanks
Baoquan

> [1] https://docs.kernel.org/powerpc/firmware-assisted-dump.html
> 
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
> ---
>  include/linux/crash_dump.h | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> index 0f3a656293b0..1052a0faf0dd 100644
> --- a/include/linux/crash_dump.h
> +++ b/include/linux/crash_dump.h
> @@ -50,6 +50,7 @@ void vmcore_cleanup(void);
>  #define vmcore_elf64_check_arch(x) (elf_check_arch(x) || vmcore_elf_check_arch_cross(x))
>  #endif
>  
> +#ifndef is_kdump_kernel
>  /*
>   * is_kdump_kernel() checks whether this kernel is booting after a panic of
>   * previous kernel or not. This is determined by checking if previous kernel
> @@ -64,6 +65,19 @@ static inline bool is_kdump_kernel(void)
>  {
>  	return elfcorehdr_addr != ELFCORE_ADDR_MAX;
>  }
> +#endif
> +
> +/*
> + * Return true if this is a dump capture kernel, where vmcore needs to be
> + * exported, irrespective of the dump capture mechanism in use.
> + *
> + * Same as is_kdump_kernel() unless arch specific code defines is_kdump_kernel()
> + * differently while supporting other dump capturing mechanisms.
> + */
> +static inline bool is_crashdump_kernel(void)
> +{
> +	return elfcorehdr_addr != ELFCORE_ADDR_MAX;
> +}
>  
>  /* is_vmcore_usable() checks if the kernel is booting after a panic and
>   * the vmcore region is usable.
> @@ -75,7 +89,7 @@ static inline bool is_kdump_kernel(void)
>  
>  static inline int is_vmcore_usable(void)
>  {
> -	return is_kdump_kernel() && elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
> +	return is_crashdump_kernel() && elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
>  }
>  
>  /* vmcore_unusable() marks the vmcore as unusable,
> @@ -84,7 +98,7 @@ static inline int is_vmcore_usable(void)
>  
>  static inline void vmcore_unusable(void)
>  {
> -	if (is_kdump_kernel())
> +	if (is_crashdump_kernel())
>  		elfcorehdr_addr = ELFCORE_ADDR_ERR;
>  }
>  
> -- 
> 2.41.0
>

Hi Baoquan,

Thanks for the review...

On 03/09/23 9:06 am, Baoquan He wrote:
> Hi Hari,
> 
> On 09/02/23 at 12:34am, Hari Bathini wrote:
>> Currently, is_kdump_kernel() returns true when elfcorehdr_addr is set.
>> While elfcorehdr_addr is set for kexec based kernel dump mechanism,
>> alternate dump capturing methods like fadump [1] also set it to export
>> the vmcore. is_kdump_kernel() is used to restrict resources in crash
>> dump capture kernel but such restrictions may not be desirable for
>> fadump. Allow is_kdump_kernel() to be defined differently for such
>> scenarios. With this, is_kdump_kernel() could be false while vmcore
>> is usable. So, introduce is_crashdump_kernel() to return true when
>> elfcorehdr_addr is set and use it for vmcore related checks.
> 
> I got what is done in these two patches, but didn't get why they need be
> done. vmcore_unusable()/is_vmcore_usable() are only unitilized in ia64.
> Why do you care if it's is_crashdump_kernel() or is_kdump_kernel()?
> If you want to override the generic is_kdump_kernel() with powerpc's own
> is_kdump_kernel(), your below change is enough to allow you to do that.
> I can't see why is_crashdump_kernel() is needed. Could you explain that
> specifically?

You mean to just remove is_kdump_kernel() check in is_vmcore_usable() &
vmcore_unusable() functions? Replaced generic is_crashdump_kernel()
function instead, that returns true for any dump capturing method,
irrespective of whether is_kdump_kernel() returns true or false.
For fadump case, is_kdump_kernel() will return false after patch 2/2.

Thanks
Hari

On 09/04/23 at 08:04pm, Hari Bathini wrote:
> Hi Baoquan,
> 
> Thanks for the review...
> 
> On 03/09/23 9:06 am, Baoquan He wrote:
> > Hi Hari,
> > 
> > On 09/02/23 at 12:34am, Hari Bathini wrote:
> > > Currently, is_kdump_kernel() returns true when elfcorehdr_addr is set.
> > > While elfcorehdr_addr is set for kexec based kernel dump mechanism,
> > > alternate dump capturing methods like fadump [1] also set it to export
> > > the vmcore. is_kdump_kernel() is used to restrict resources in crash
> > > dump capture kernel but such restrictions may not be desirable for
> > > fadump. Allow is_kdump_kernel() to be defined differently for such
> > > scenarios. With this, is_kdump_kernel() could be false while vmcore
> > > is usable. So, introduce is_crashdump_kernel() to return true when
> > > elfcorehdr_addr is set and use it for vmcore related checks.
> > 
> > I got what is done in these two patches, but didn't get why they need be
> > done. vmcore_unusable()/is_vmcore_usable() are only unitilized in ia64.
> > Why do you care if it's is_crashdump_kernel() or is_kdump_kernel()?
> > If you want to override the generic is_kdump_kernel() with powerpc's own
> > is_kdump_kernel(), your below change is enough to allow you to do that.
> > I can't see why is_crashdump_kernel() is needed. Could you explain that
> > specifically?
> 
> You mean to just remove is_kdump_kernel() check in is_vmcore_usable() &
> vmcore_unusable() functions? Replaced generic is_crashdump_kernel()
> function instead, that returns true for any dump capturing method,
> irrespective of whether is_kdump_kernel() returns true or false.
> For fadump case, is_kdump_kernel() will return false after patch 2/2.

OK, I could understand what you want to achieve. You want to make
is_kdump_kernel() only return true for kdump, while is_vmcore_usable()
returns true for both kdump and fadump.

IIUC, can we change as below? It could make code clearer and more
straightforward. I don't think adding another is_crashdump_kernel()
is a good idea, that would be a torture for non-powerpc people reading
code when they need differentiate between kdump and crashdump.

diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
index 0f3a656293b0..102a8b710b38 100644
--- a/include/linux/crash_dump.h
+++ b/include/linux/crash_dump.h
@@ -50,6 +50,7 @@ void vmcore_cleanup(void);
 #define vmcore_elf64_check_arch(x) (elf_check_arch(x) || vmcore_elf_check_arch_cross(x))
 #endif
 
+#ifndef is_kdump_active
 /*
  * is_kdump_kernel() checks whether this kernel is booting after a panic of
  * previous kernel or not. This is determined by checking if previous kernel
@@ -64,6 +65,14 @@ static inline bool is_kdump_kernel(void)
 {
 	return elfcorehdr_addr != ELFCORE_ADDR_MAX;
 }
+#endif
+
+#ifndef is_fadump_active
+static inline bool is_fadump_active(void)
+{
+	return false;
+}
+#endif
 
 /* is_vmcore_usable() checks if the kernel is booting after a panic and
  * the vmcore region is usable.
@@ -75,7 +84,8 @@ static inline bool is_kdump_kernel(void)
 
 static inline int is_vmcore_usable(void)
 {
-	return is_kdump_kernel() && elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
+	return (is_kdump_kernel() || is_fadump_active())
+		&& elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0;
 }
 
 /* vmcore_unusable() marks the vmcore as unusable,
@@ -84,7 +94,7 @@ static inline int is_vmcore_usable(void)
 
 static inline void vmcore_unusable(void)
 {
-	if (is_kdump_kernel())
+	if (is_kdump_kernel() || is_fadump_active())
 		elfcorehdr_addr = ELFCORE_ADDR_ERR;
 }

On 05/09/23 8:00 am, Baoquan He wrote:
> On 09/04/23 at 08:04pm, Hari Bathini wrote:
>> Hi Baoquan,
>>
>> Thanks for the review...
>>
>> On 03/09/23 9:06 am, Baoquan He wrote:
>>> Hi Hari,
>>>
>>> On 09/02/23 at 12:34am, Hari Bathini wrote:
>>>> Currently, is_kdump_kernel() returns true when elfcorehdr_addr is set.
>>>> While elfcorehdr_addr is set for kexec based kernel dump mechanism,
>>>> alternate dump capturing methods like fadump [1] also set it to export
>>>> the vmcore. is_kdump_kernel() is used to restrict resources in crash
>>>> dump capture kernel but such restrictions may not be desirable for
>>>> fadump. Allow is_kdump_kernel() to be defined differently for such
>>>> scenarios. With this, is_kdump_kernel() could be false while vmcore
>>>> is usable. So, introduce is_crashdump_kernel() to return true when
>>>> elfcorehdr_addr is set and use it for vmcore related checks.
>>>
>>> I got what is done in these two patches, but didn't get why they need be
>>> done. vmcore_unusable()/is_vmcore_usable() are only unitilized in ia64.
>>> Why do you care if it's is_crashdump_kernel() or is_kdump_kernel()?
>>> If you want to override the generic is_kdump_kernel() with powerpc's own
>>> is_kdump_kernel(), your below change is enough to allow you to do that.
>>> I can't see why is_crashdump_kernel() is needed. Could you explain that
>>> specifically?
>>
>> You mean to just remove is_kdump_kernel() check in is_vmcore_usable() &
>> vmcore_unusable() functions? Replaced generic is_crashdump_kernel()
>> function instead, that returns true for any dump capturing method,
>> irrespective of whether is_kdump_kernel() returns true or false.
>> For fadump case, is_kdump_kernel() will return false after patch 2/2.
> 
> OK, I could understand what you want to achieve. You want to make
> is_kdump_kernel() only return true for kdump, while is_vmcore_usable()
> returns true for both kdump and fadump.
> 
> IIUC, can we change as below? It could make code clearer and more
> straightforward. I don't think adding another is_crashdump_kernel()
> is a good idea, that would be a torture for non-powerpc people reading
> code when they need differentiate between kdump and crashdump.
> 

Sure, Baoquan.
Posted v2 based on your suggestion.

Thanks
Hari