linux-kernel - Re: [PATCH] for_each macros correctness

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Message-ID: <1390759506.6778.1.camel@laptop>
Date:	Sun, 26 Jan 2014 16:05:06 -0200
From:	Jose Alonso <joalonsof@...il.com>
To:	Fubo Chen <fubo.chen@...il.com>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Lukasz Dorau <lukasz.dorau@...el.com>,
	Maciej Patelczyk <maciej.patelczyk@...el.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] for_each macros correctness

On Sun, 2014-01-26 at 14:39 +0100, Fubo Chen wrote:
> On Sun, Jan 26, 2014 at 11:54 AM, Jose Alonso <joalonsof@...il.com> wrote:
> > I observed that there are for_each macros that do an extra memory access
> > beyond the defined area.
> > Normally this does not cause problems.
> > But, this can cause exceptions. For example: if the area is allocated at
> > the end of a page and the next page is not accessible.
> >
> > For correctness, I suggest changing the arguments of the 'for loop' like
> > others 'for_each' do in the kernel.
> 
> Does this patch fix a kernel crash when using gcc 4.8 like the patch
> in http://lkml.org/lkml/2014/1/21/146 ?

The patch for 'for_each_isci_host' is equivalent.

I followed the link above, and as I understand: The access to 
to_pci_info(pdev)->hosts[2] do not caused exception, but
the fact of hosts[2] is "logically accessed" "confused" the
gcc 4.8 compiler. (The gcc compiler do very aggressive loop
optimization and can eliminate loops executing each pass
linearly).


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