linux-kernel - Re: [PATCH] mm: drop VM_BUG_ON from __get_free

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Message-ID: <e0f4426d-1b7c-e590-aae0-e8f7ae3bb948@suse.cz>
Date:   Wed, 27 Jun 2018 09:50:01 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     JianKang Chen <chenjiankang1@...wei.com>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, xieyisheng1@...wei.com,
        guohanjun@...wei.com, wangkefeng.wang@...wei.com
Subject: Re: [PATCH] mm: drop VM_BUG_ON from __get_free_pages

On 06/27/2018 09:34 AM, Michal Hocko wrote:
> On Tue 26-06-18 10:04:16, Andrew Morton wrote:
> 
> And as I've argued before the code would be wrong regardless. We would
> leak the memory or worse touch somebody's else kmap without knowing
> that.  So we have a choice between a mem leak, data corruption k or a
> silent fixup. I would prefer the last option. And blowing up on a BUG
> is not much better on something that is easily fixable. I am not really
> convinced that & ~__GFP_HIGHMEM is something to lose sleep over.

Maybe put the fixup into a "#ifdef CONFIG_HIGHMEM" block and then modern
systems won't care? In that case it could even be if (WARN_ON_ONCE(...))
so future cases with wrong expectations would become known.

Vlastimil