linux-kernel - Re: [PATCH] fork: Improve error message for corrupted page tables

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Date:   Wed, 31 Jul 2019 15:36:49 -0700
From:   Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        dave.hansen@...el.com, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] fork: Improve error message for corrupted page tables


> > With patch:
> > -----------
> > [   69.815453] mm/pgtable-generic.c:29: bad p4d
> > 0000000084653642(800000025ca37467)
> > [   69.815872] BUG: Bad rss-counter state mm:00000000014a6c03
> > type:MM_FILEPAGES val:2
> > [   69.815962] BUG: Bad rss-counter state mm:00000000014a6c03
> > type:MM_ANONPAGES val:5
> > [   69.816050] BUG: non-zero pgtables_bytes on freeing mm: 20480
> 
> Seems useful.
> 
> > --- a/include/linux/mm_types_task.h
> > +++ b/include/linux/mm_types_task.h
> > @@ -44,6 +44,13 @@ enum {
> >  	NR_MM_COUNTERS
> >  };
> >  
> > +static const char * const resident_page_types[NR_MM_COUNTERS] = {
> > +	"MM_FILEPAGES",
> > +	"MM_ANONPAGES",
> > +	"MM_SWAPENTS",
> > +	"MM_SHMEMPAGES",
> > +};
> 
> But please let's not put this in a header file.  We're asking the
> compiler to put a copy of all of this into every compilation unit which
> includes the header.  Presumably the compiler is smart enough not to
> do that, but it's not good practice.

Thanks for the explanation. Makes sense to me.

Just wanted to check before sending V2,
Is it OK if I add this to kernel/fork.c? or do you have something else in
mind?

Regards,
Sai