linux-kernel - Re: [PATCH v3 1/2] vmcore: remove dependency with is_kdump

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Message-ID: <ZQKO1ckVu0Xj1abW@MiWiFi-R3L-srv>
Date:   Thu, 14 Sep 2023 12:40:53 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Hari Bathini <hbathini@...ux.ibm.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Dave Young <dyoung@...hat.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v3 1/2] vmcore: remove dependency with is_kdump_kernel()
 for exporting vmcore

On 09/12/23 at 01:59pm, 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. Since, is_kdump_kernel() is used to restrict resources in
> crash dump capture kernel and 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, remove unnecessary dependency with is_kdump_kernel(), for
> exporting vmcore.
> 
> [1] https://docs.kernel.org/powerpc/firmware-assisted-dump.html
> 
> Suggested-by: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>
> ---
> 
> Changes in v3:
> * Decoupled is_vmcore_usable() & vmcore_unusable() from is_kdump_kernel()
>   as suggested here: 
>     https://lore.kernel.org/linuxppc-dev/ZP7si3UMVpPfYV+w@MiWiFi-R3L-srv/T/#m13ae5a7e4ba6f4d8397f0f66581832292eee3a85
> 
> 
>  include/linux/crash_dump.h | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)

LGTM,

Acked-by: Baoquan He <bhe@...hat.com>

> 
> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> index 0f3a656293b0..acc55626afdc 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 +65,7 @@ static inline bool is_kdump_kernel(void)
>  {
>  	return elfcorehdr_addr != ELFCORE_ADDR_MAX;
>  }
> +#endif
>  
>  /* is_vmcore_usable() checks if the kernel is booting after a panic and
>   * the vmcore region is usable.
> @@ -75,7 +77,8 @@ 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 elfcorehdr_addr != ELFCORE_ADDR_ERR &&
> +		elfcorehdr_addr != ELFCORE_ADDR_MAX ? 1 : 0;
>  }
>  
>  /* vmcore_unusable() marks the vmcore as unusable,
> @@ -84,8 +87,7 @@ static inline int is_vmcore_usable(void)
>  
>  static inline void vmcore_unusable(void)
>  {
> -	if (is_kdump_kernel())
> -		elfcorehdr_addr = ELFCORE_ADDR_ERR;
> +	elfcorehdr_addr = ELFCORE_ADDR_ERR;
>  }
>  
>  /**
> -- 
> 2.41.0
>