linux-kernel - Re: [PATCH] video: limit stack usage of ir-kbd-i2c.c

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Date:	Tue, 26 Feb 2008 22:03:16 +0100
From:	Marcin Slusarz <marcin.slusarz@...il.com>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	i2c@...sensors.org, video4linux-list@...hat.com
Subject: Re: [PATCH] video: limit stack usage of ir-kbd-i2c.c

On Tue, Feb 26, 2008 at 01:32:22PM +0100, Jean Delvare wrote:
> Hi Marcin,
> 
> On Mon, 25 Feb 2008 21:51:00 +0100, Marcin Slusarz wrote:
> > ir_probe allocated struct i2c_client on stack;
> > it's pretty big structure, so allocate it with kzalloc
> > 
> > make checkstack output without this patch:
> > x059d ir_probe [ir-kbd-i2c]:                           1000
> > 
> > compile tested only
> > 
> > Signed-off-by: Marcin Slusarz <marcin.slusarz@...il.com>
> > Cc: Mauro Carvalho Chehab <mchehab@...radead.org>
> > Cc: Jean Delvare <khali@...ux-fr.org>
> > ---
> >  drivers/media/video/ir-kbd-i2c.c |   18 +++++++++++-------
> >  1 files changed, 11 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/media/video/ir-kbd-i2c.c b/drivers/media/video/ir-kbd-i2c.c
> > index 9851987..aec122f 100644
> > --- a/drivers/media/video/ir-kbd-i2c.c
> > +++ b/drivers/media/video/ir-kbd-i2c.c
> > @@ -510,9 +510,9 @@ static int ir_probe(struct i2c_adapter *adap)
> >  	static const int probe_cx88[] = { 0x18, 0x6b, 0x71, -1 };
> >  	static const int probe_cx23885[] = { 0x6b, -1 };
> >  	const int *probe = NULL;
> > -	struct i2c_client c;
> > +	struct i2c_client *c;
> >  	unsigned char buf;
> > -	int i,rc;
> > +	int i, rc;
> >  
> >  	switch (adap->id) {
> >  	case I2C_HW_B_BT848:
> > @@ -537,19 +537,23 @@ static int ir_probe(struct i2c_adapter *adap)
> >  	if (NULL == probe)
> >  		return 0;
> >  
> > -	memset(&c,0,sizeof(c));
> > -	c.adapter = adap;
> > +	c = kzalloc(sizeof(*c), GFP_KERNEL);
> > +	if (!c)
> > +		return -ENOMEM;
> > +
> > +	c->adapter = adap;
> >  	for (i = 0; -1 != probe[i]; i++) {
> > -		c.addr = probe[i];
> > -		rc = i2c_master_recv(&c,&buf,0);
> > +		c->addr = probe[i];
> > +		rc = i2c_master_recv(c, &buf, 0);
> >  		dprintk(1,"probe 0x%02x @ %s: %s\n",
> >  			probe[i], adap->name,
> >  			(0 == rc) ? "yes" : "no");
> >  		if (0 == rc) {
> > -			ir_attach(adap,probe[i],0,0);
> > +			ir_attach(adap, probe[i], 0, 0);
> >  			break;
> >  		}
> >  	}
> > +	kfree(c);
> >  	return 0;
> >  }
> >  
> 
> While this works, I'd rather change the code to call i2c_transfer()
> instead of i2c_master_recv(). i2c_transfer() is meant exactly for this
> case (no i2c_client at hand.) This solves the stack usage problem
> without requiring a temporary memory allocation:
> 
> * * * * *
> 
> Limit stack usage in ir_probe by calling i2c_transfer, which doesn't
> require a struct i2c_client, instead of i2c_master_recv which does.
> 
> Signed-off-by: Jean Delvare <khali@...ux-fr.org>
> ---
>  drivers/media/video/ir-kbd-i2c.c |   17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> --- linux-2.6.25-rc3.orig/drivers/media/video/ir-kbd-i2c.c	2008-02-26 11:35:51.000000000 +0100
> +++ linux-2.6.25-rc3/drivers/media/video/ir-kbd-i2c.c	2008-02-26 11:44:54.000000000 +0100
> @@ -510,8 +510,11 @@ static int ir_probe(struct i2c_adapter *
>  	static const int probe_cx88[] = { 0x18, 0x6b, 0x71, -1 };
>  	static const int probe_cx23885[] = { 0x6b, -1 };
>  	const int *probe = NULL;
> -	struct i2c_client c;
> -	unsigned char buf;
> +	struct i2c_msg msg = {
> +		.flags = I2C_M_RD,
> +		.len = 0,
> +		.buf = NULL,
> +	};
>  	int i,rc;
>  
>  	switch (adap->id) {
> @@ -537,15 +540,13 @@ static int ir_probe(struct i2c_adapter *
>  	if (NULL == probe)
>  		return 0;
>  
> -	memset(&c,0,sizeof(c));
> -	c.adapter = adap;
>  	for (i = 0; -1 != probe[i]; i++) {
> -		c.addr = probe[i];
> -		rc = i2c_master_recv(&c,&buf,0);
> +		msg.addr = probe[i];
> +		rc = i2c_transfer(adap, &msg, 1);
>  		dprintk(1,"probe 0x%02x @ %s: %s\n",
>  			probe[i], adap->name,
> -			(0 == rc) ? "yes" : "no");
> -		if (0 == rc) {
> +			(1 == rc) ? "yes" : "no");
> +		if (1 == rc) {
>  			ir_attach(adap,probe[i],0,0);
>  			break;
>  		}
> 
> 
> Built-tested, I've also tested loading the ir-kbd-i2c driver on an
> unsupported cx88 adapter. Review and more testing welcome.
I know nothing about I2C API, so I can't comment on correctness of this patch ;)

Do you have an idea (or patch :D) how to solve this:
0x00000234 v4l_compat_translate_ioctl [v4l1-compat]:    1376
? That's on top of my make checkstack output

Marcin
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