Date: Tue, 18 Nov 2014 15:34:24 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Seth Jennings <sjennings@variantweb.net>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Nitin Gupta <ngupta@vflare.org>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Dan Streetman <ddstreet@ieee.org>,
        Jerome Marchand <jmarchan@redhat.com>
Subject: Re: [PATCH] zsmalloc: correct fragile [kmap|kunmap]_atomic use
Message-Id: <20141118153424.70899732d4ed7933892b6055@linux-foundation.org>
In-Reply-To: <20141118232139.GA7393@bbox>
References: <1415927461-14220-1-git-send-email-minchan@kernel.org>
	<20141114150732.GA2402@cerebellum.variantweb.net>
	<20141118150138.668c81fda55c3ce39d7b2aac@linux-foundation.org>
	<20141118232139.GA7393@bbox>
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Sender: linux-kernel-owner@vger.kernel.org

On Wed, 19 Nov 2014 08:21:39 +0900 Minchan Kim <minchan@kernel.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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