linux-kernel - Re: [PATCH V2] fork: Improve error message for corrupted page tables

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Message-ID: <73b77479-cdd2-6d53-14ae-25ec4c4c3d25@intel.com>
Date:   Tue, 6 Aug 2019 09:30:45 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Ingo Molnar <mingo@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH V2] fork: Improve error message for corrupted page tables

On 8/5/19 8:05 PM, Sai Praneeth Prakhya wrote:
> +static const char * const resident_page_types[NR_MM_COUNTERS] = {
> +	[MM_FILEPAGES]		= "MM_FILEPAGES",
> +	[MM_ANONPAGES]		= "MM_ANONPAGES",
> +	[MM_SWAPENTS]		= "MM_SWAPENTS",
> +	[MM_SHMEMPAGES]		= "MM_SHMEMPAGES",
> +};

One trick to ensure that this gets updated if the names are ever
updated.  You can do:

#define NAMED_ARRAY_INDEX(x)	[x] = __stringify(x),

and

static const char * const resident_page_types[NR_MM_COUNTERS] = {
	NAMED_ARRAY_INDEX(MM_FILE_PAGES),
	NAMED_ARRAY_INDEX(MM_SHMEMPAGES),
	...
};

That makes sure that any name changes make it into the strings.  Then
stick a:

	BUILD_BUG_ON(NR_MM_COUNTERS != ARRAY_SIZE(resident_page_types));

somewhere.  That makes sure that any new array indexes get a string
added in the array.  Otherwise you get nice, early, compile-time errors.