linux-kernel - [PATCH 3.2 02/59] [media] pvrusb2: reduce stack usage pvr2_eeprom

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Message-ID: <lsq.1503061993.705459509@decadent.org.uk>
Date:   Fri, 18 Aug 2017 14:13:13 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Arnd Bergmann" <arnd@...db.de>,
        "Mauro Carvalho Chehab" <mchehab@...pensource.com>,
        "Hans Verkuil" <hans.verkuil@...co.com>
Subject: [PATCH 3.2 02/59] [media] pvrusb2: reduce stack usage
 pvr2_eeprom_analyze()

3.2.92-rc1 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.

Fixes: d855497edbfb ("V4L/DVB (4228a): pvrusb2 to kernel 2.6.18")

Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Hans Verkuil <hans.verkuil@...co.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@...pensource.com>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/media/video/pvrusb2/pvrusb2-eeprom.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

--- a/drivers/media/video/pvrusb2/pvrusb2-eeprom.c
+++ b/drivers/media/video/pvrusb2/pvrusb2-eeprom.c
@@ -123,15 +123,10 @@ int pvr2_eeprom_analyze(struct pvr2_hdw
 	memset(&tvdata,0,sizeof(tvdata));
 
 	eeprom = pvr2_eeprom_fetch(hdw);
-	if (!eeprom) return -EINVAL;
+	if (!eeprom)
+		return -EINVAL;
 
-	{
-		struct i2c_client fake_client;
-		/* Newer version expects a useless client interface */
-		fake_client.addr = hdw->eeprom_addr;
-		fake_client.adapter = &hdw->i2c_adap;
-		tveeprom_hauppauge_analog(&fake_client,&tvdata,eeprom);
-	}
+	tveeprom_hauppauge_analog(NULL, &tvdata, eeprom);
 
 	trace_eeprom("eeprom assumed v4l tveeprom module");
 	trace_eeprom("eeprom direct call results:");