linux-kernel - Re: [PATCH 4.4 16/30] [media] pvrusb2: reduce stack usage pvr2_eeprom

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Message-ID: <1498752917.1935.52.camel@codethink.co.uk>
Date:   Thu, 29 Jun 2017 17:15:17 +0100
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>
Subject: Re: [PATCH 4.4 16/30] [media] pvrusb2: reduce stack usage
 pvr2_eeprom_analyze()

On Mon, 2017-06-19 at 23:20 +0800, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Arnd Bergmann <arnd@...db.de>
> 
> commit 6830733d53a4517588e56227b9c8538633f0c496 upstream.
> 
> The driver uses a relatively large data structure on the stack, which
> showed up on my radar as we get a warning with the "latent entropy"
> GCC plugin:
> 
> drivers/media/usb/pvrusb2/pvrusb2-eeprom.c:153:1: error: the frame size of 1376 bytes is larger than 1152 bytes [-Werror=frame-larger-than=]
> 
> The warning is usually hidden as we raise the warning limit to 2048
> when the plugin is enabled, but I'd like to lower that again in the
> future, and making this function smaller helps to do that without
> build regressions.
> 
> Further analysis shows that putting an 'i2c_client' structure on
> the stack is not really supported, as the embedded 'struct device'
> is not initialized here, and we are only saved by the fact that
> the function that is called here does not use the pointer at all.
[...]

That is not true in 4.4-stable.  This commit depends on:

commit 6037b3ca28f4258d913dbe77248fd77827702ae3
Author: Mauro Carvalho Chehab <mchehab@...pensource.com>
Date:   Wed Nov 16 14:21:48 2016 -0200

    [media] tveeprom: print log messages using pr_foo()

Ben.

-- 
Ben Hutchings
Software Developer, Codethink Ltd.