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

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Message-ID: <20170703073153.GE5888@kroah.com>
Date:   Mon, 3 Jul 2017 09:31:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Ben Hutchings <ben.hutchings@...ethink.co.uk>
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 Thu, Jun 29, 2017 at 05:15:17PM +0100, Ben Hutchings wrote:
> 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()

It does?  I don't understand how the two are connected.  Removing
i2c_client off of the stack is a good thing.  Ah, I see how the pointer
is used in tveeprom_hauppauge_analog(), but this shouldn't matter here,
right?

thanks,

greg k-h