linux-kernel - Re: [3/4] powerpc/mm: Clean up memory hotplug failure paths

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Message-ID: <20160301022741.GK5427@voom.redhat.com>
Date:	Tue, 1 Mar 2016 13:27:41 +1100
From:	David Gibson <david@...son.dropbear.id.au>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	paulus@...ba.org, benh@...nel.crashing.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [3/4] powerpc/mm: Clean up memory hotplug failure paths

On Tue, Mar 01, 2016 at 12:59:07PM +1100, Michael Ellerman wrote:
> On Tue, 2016-09-02 at 03:32:42 UTC, 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.
> >
> ...
> > diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> > index baa1a23..fbc9448 100644
> > --- a/arch/powerpc/mm/init_64.c
> > +++ b/arch/powerpc/mm/init_64.c
> > @@ -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);
> 
> This breaks the build when CONFIG_MEMORY_HOTPLUG=n, because
> htab_remove_mapping() is not defined.
> 
> The obvious fix of moving htab_remove_mapping() out of CONFIG_MEMORY_HOTPLUG
> works, so I'll do that unless anyone objects.

Sounds good, thanks for the catch.

-- 
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

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