Subject: Re: [RFCv2 4/9] arch/powerpc: Clean up memory hotplug failure paths

From: David Gibson <[email-masked]>
Date: Wed, 3 Feb 2016 15:31:59 +1100

On Tue, Feb 02, 2016 at 09:04:23AM -0600, Nathan Fontenot wrote:
> On 01/28/2016 11:23 PM, David Gibson wrote:
> > This makes a number of cleanups to handling of mapping failures during
> > memory hotplug on Power:
> > 
> > For errors creating the linear mapping for the hot-added region:
> >   * This is now reported with EFAULT which is more appropriate than the
> >     previous EINVAL (the failure is unlikely to be related to the
> >     function's parameters)
> >   * An error in this path now prints a warning message, rather than just
> >     silently failing to add the extra memory.
> >   * Previously a failure here could result in the region being partially
> >     mapped.  We now clean up any partial mapping before failing.
> > 
> > For errors creating the vmemmap for the hot-added region:
> >    * This is now reported with EFAULT instead of causing a BUG() - this
> >      could happen for external reason (e.g. full hash table) so it's better
> >      to handle this non-fatally
> >    * An error message is also printed, so the failure won't be silent
> >    * As above a failure could cause a partially mapped region, we now
> >      clean this up.
> > 
> > Signed-off-by: David Gibson <[email-masked]>
> > ---
> >  arch/powerpc/mm/hash_utils_64.c | 13 ++++++++++---
> >  arch/powerpc/mm/init_64.c       | 38 ++++++++++++++++++++++++++------------
> >  arch/powerpc/mm/mem.c           | 10 ++++++++--
> >  3 files changed, 44 insertions(+), 17 deletions(-)
> > 
> > diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> > index 0737eae..e88a86e 100644
> > --- a/arch/powerpc/mm/hash_utils_64.c
> > +++ b/arch/powerpc/mm/hash_utils_64.c
> > @@ -635,9 +635,16 @@ static unsigned long __init htab_get_table_size(void)
> >  #ifdef CONFIG_MEMORY_HOTPLUG
> >  int create_section_mapping(unsigned long start, unsigned long end)
> >  {
> > -	return htab_bolt_mapping(start, end, __pa(start),
> > -				 pgprot_val(PAGE_KERNEL), mmu_linear_psize,
> > -				 mmu_kernel_ssize);
> > +	int rc = htab_bolt_mapping(start, end, __pa(start),
> > +				   pgprot_val(PAGE_KERNEL), mmu_linear_psize,
> > +				   mmu_kernel_ssize);
> > +
> > +	if (rc < 0) {
> > +		int rc2 = htab_remove_mapping(start, end, mmu_linear_psize,
> > +					      mmu_kernel_ssize);
> > +		BUG_ON(rc2 && (rc2 != -ENOENT));
> > +	}
> > +	return rc;
> >  }
> >  
> 
> <-- snip -->
> 
> >  #ifdef CONFIG_MEMORY_HOTPLUG
> > @@ -217,15 +219,20 @@ static void vmemmap_remove_mapping(unsigned long start,
> >  }
> >  #endif
> >  #else /* CONFIG_PPC_BOOK3E */
> > -static void __meminit vmemmap_create_mapping(unsigned long start,
> > -					     unsigned long page_size,
> > -					     unsigned long phys)
> > +static int __meminit vmemmap_create_mapping(unsigned long start,
> > +					    unsigned long page_size,
> > +					    unsigned long phys)
> >  {
> > -	int  mapped = htab_bolt_mapping(start, start + page_size, phys,
> > -					pgprot_val(PAGE_KERNEL),
> > -					mmu_vmemmap_psize,
> > -					mmu_kernel_ssize);
> > -	BUG_ON(mapped < 0);
> > +	int rc = htab_bolt_mapping(start, start + page_size, phys,
> > +				   pgprot_val(PAGE_KERNEL),
> > +				   mmu_vmemmap_psize, mmu_kernel_ssize);
> > +	if (rc < 0) {
> > +		int rc2 = htab_remove_mapping(start, start + page_size,
> > +					      mmu_vmemmap_psize,
> > +					      mmu_kernel_ssize);
> > +		BUG_ON(rc2 && (rc2 != -ENOENT));
> > +	}
> > +	return rc;
> >  }
> >  
> 
> If I'm reading this correctly it appears that create_section_mapping() and
> vmemmap_create_mapping() for !PPC_BOOK3E are identical. Any reason to not
> have one routine, perhaps just have vmemmap_create_mapping() just call
> create_section_mapping()?

Not really, apart from documenting what they're used for.  They're
both fairly trivial wrappers around htab_bolt_mapping().  I think
cleaning this up is outside the scope of this series though.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson