linux-kernel - Re: [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under

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Date:   Tue, 14 Aug 2018 12:06:44 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     David Hildenbrand <david@...hat.com>
Cc:     akpm@...ux-foundation.org, mhocko@...e.com,
        dan.j.williams@...el.com, jglisse@...hat.com, rafael@...nel.org,
        yasu.isimatu@...il.com, logang@...tatee.com, dave.jiang@...el.com,
        Jonathan.Cameron@...wei.com, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from
 unregister_mem_sect_under_nodes

On Tue, Aug 14, 2018 at 11:44:50AM +0200, David Hildenbrand wrote:
> 
> Yes I know, as I said, if it would be local to a file I would not care.
> Making this functions never return an error is nice, though (and as you
> noted, the return value is never checked).
> 
> I am a friend of stating which conditions a function expects to hold if
> a function can be called from other parts of the system. Usually I
> prefer to use BUG_ONs for that (whoever decides to call it can directly
> see what he as to check before calling) or comments. But comments tend
> to become obsolete.

Uhm, I think a BUG_ON is too much here.
We could replace the check with a WARN_ON, just in case
a new function decides to call unregister_mem_sect_under_nodes() in the future.

Something like:

WARN_ON(!mem_blk)
	return;

In that case, we should get a nice splat in the logs that should tell us
who is calling it with an invalid mem_blk.

-- 
Oscar Salvador
SUSE L3