linux-kernel - Re: [PATCH v2 2/3] vmcore: allow fadump to export vmcore even if is_kdump

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Date:   Mon, 11 Sep 2023 18:31:39 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Hari Bathini <hbathini@...ux.ibm.com>,
        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>
Subject: Re: [PATCH v2 2/3] vmcore: allow fadump to export vmcore even if
 is_kdump_kernel() is false

On 09/11/23 at 05:13pm, Michael Ellerman wrote:
> Hari Bathini <hbathini@...ux.ibm.com> writes:
> > 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 are not desirable for
> > fadump, allow is_kdump_kernel() to be defined differently for fadump
> > case. With that change, include is_fadump_active() check in functions
> > is_vmcore_usable() & vmcore_unusable() to be able to export vmcore for
> > fadump case too.
> ...
> > diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> > index 0f3a656293b0..de8a9fabfb6f 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
> > +
> > +#ifndef is_fadump_active
> > +/*
> > + * If f/w assisted dump capturing mechanism (fadump), instead of kexec based
> > + * dump capturing mechanism (kdump) is exporting the vmcore, then this function
> > + * will be defined in arch specific code to return true, when appropriate.
> > + */
> > +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 +89,8 @@ 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 +99,7 @@ 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;
> >  }
> 
> I think it would be cleaner to decouple is_vmcore_usable() and
> vmcore_usable() from is_kdump_kernel().
> 
> ie, make them operate solely based on the value of elforehdr_addr:
> 
> static inline int is_vmcore_usable(void)
> {
> 	elfcorehdr_addr != ELFCORE_ADDR_ERR && \
> 		elfcorehdr_addr != ELFCORE_ADDR_MAX;

Agree. I fell into the blind corner of thinking earlier. Above change
is better.

> }
> 
> static inline void vmcore_unusable(void)
> {
> 	elfcorehdr_addr = ELFCORE_ADDR_ERR;
> }
> 
> 
> Then all we need on powerpc is a way to override is_kdump_kernel().
> 
> cheers
>