linux-kernel - Re: [PATCH] zsmalloc: correct fragile [kmap|kunmap]

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Date:	Tue, 18 Nov 2014 15:34:24 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Seth Jennings <sjennings@...iantweb.net>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Dan Streetman <ddstreet@...e.org>,
	Jerome Marchand <jmarchan@...hat.com>
Subject: Re: [PATCH] zsmalloc: correct fragile [kmap|kunmap]_atomic use

On Wed, 19 Nov 2014 08:21:39 +0900 Minchan Kim <minchan@...nel.org> wrote:

> Main reason I sent the patch is I got a subtle bug when I implement
> new feature of zsmalloc(ie, compaction) due to link's mishandling
> (ie, link was over page boundary by my fault).
> Although it was totally my mistake, it took time for a while
> to find a root cause because unpredictable kmapped address should
> be unmapped so it's almost random crash.

Fair enough.

That's pretty rude behaviour from kunmap_atomic().  Unfortunately it
just doesn't have anything with which to check the address - we'd need
to create a special per-cpu array[KM_TYPE_NR] just for the purpose.
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