Message-ID: <1390759506.6778.1.camel@laptop>
Subject: Re: [PATCH] for_each macros correctness
From: Jose Alonso <joalonsof@gmail.com>
To: Fubo Chen <fubo.chen@gmail.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Lukasz Dorau <lukasz.dorau@intel.com>,
        Maciej Patelczyk <maciej.patelczyk@intel.com>,
        Dave Jiang <dave.jiang@intel.com>, Simon Horman <horms@verge.net.au>,
        Magnus Damm <magnus.damm@gmail.com>, Paul Mundt <lethal@linux-sh.org>,
        Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Guennadi Liakhovetski <g.liakhovetski@gmx.de>,
        Liam Girdwood <lgirdwood@gmail.com>, Mark Brown <broonie@kernel.org>,
        Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>
Date: Sun, 26 Jan 2014 16:05:06 -0200
In-Reply-To: <CAJAFBLBONBLnMnC3Dq8fad4vAUPJPOjp6+5TEzdUAC=Dq6x7pQ@mail.gmail.com>
References: <1390733658.3059.10.camel@laptop>
	 <CAJAFBLBONBLnMnC3Dq8fad4vAUPJPOjp6+5TEzdUAC=Dq6x7pQ@mail.gmail.com>
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On Sun, 2014-01-26 at 14:39 +0100, Fubo Chen wrote:
> On Sun, Jan 26, 2014 at 11:54 AM, Jose Alonso <joalonsof@gmail.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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