linux-kernel - Re: [GIT PULL] memblock:fix validation of NUMA coverage

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Message-ID: <CAHk-=wgOMcScTviziAbL9Z2RDduaEFdZbHsESxqUS2eFfUmUVg@mail.gmail.com>
Date: Thu, 13 Jun 2024 10:38:28 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>, Jan Beulich <jbeulich@...e.com>, Narasimhan V <Narasimhan.V@....com>, 
	"Paul E. McKenney" <paulmck@...nel.org>, stable@...r.kernel.org, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] memblock:fix validation of NUMA coverage

On Thu, 13 Jun 2024 at 10:09, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Is there some broken scripting that people have started using (or have
> been using for a while and was recently broken)?

... and then when I actually pull the code, I note that the problem
where it checked _one_ bogus value has just been replaced with
checking _another_ bogus value.

Christ.

What if people use a node ID that is simply outside the range
entirely, instead of one of those special node IDs?

And now for memblock_set_node() you should apparently use NUMA_NO_NODE
to not get a warning, but for memblock_set_region_node() apparently
the right random constant to use is MAX_NUMNODES.

Does *any* of this make sense? No.

How about instead of having two random constants - and not having any
range checking that I see - just have *one* random constant for "I
have no range", call that NUMA_NO_NODE, and then have a simple helper
for "do I have a valid range", and make that be

   static inline bool numa_valid_node(int nid)
   { return (unsigned int)nid < MAX_NUMNODES; }

or something like that? Notice that now *all* of

 - NUMA_NO_NODE (explicitly no node)

 - MAX_NUMNODES (randomly used no node)

 - out of range node (who knows wth firmware tables do?)

will get the same result from that "numa_valid_node()" function.

And at that point you don't need to care, you don't need to warn, and
you don't need to have these insane rules where "sometimes you *HAVE*
to use NUMA_NO_NODE, or we warn, in other cases MAX_NUMNODES is the
thing".

Please? IOW, instead of adding a warning for fragile code, then change
some caller to follow the new rules, JUST FIX THE STUPID FRAGILITY!

Or hey, just do

    #define NUMA_NO_NODE MAX_NUMNODES

and have two names for the *same* constant, instead fo having two
different constants with strange semantic differences that seem to
make no sense and where the memblock code itself seems to go
back-and-forth on it in different contexts.

              Linus