linux-kernel - Re: [PATCH v2 1/2] mfd: viperboard: allocate I/O buffer separately

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Date:	Tue, 23 Sep 2014 09:38:40 +0200
From:	Johan Hovold <johan@...nel.org>
To:	Octavian Purdila <octavian.purdila@...el.com>
Cc:	sameo@...ux.intel.com, lee.jones@...aro.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	johan@...nel.org
Subject: Re: [PATCH v2 1/2] mfd: viperboard: allocate I/O buffer separately

On Tue, Sep 23, 2014 at 09:35:41AM +0200, Johan Hovold wrote:
> On Mon, Sep 22, 2014 at 10:39:18PM +0300, Octavian Purdila wrote:
> > Currently the I/O buffer is allocated part of the device status
> > structure, potentially sharing the same cache line with other members
> > in this structure.
> > 
> > Allocate the buffer separately, to avoid the I/O operations corrupting
> > the device status structure due to cache line sharing.
> > 
> > Compiled tested only as I don't have access to hardware.
> > 
> > Signed-off-by: Octavian Purdila <octavian.purdila@...el.com>
> > ---
> >  drivers/mfd/viperboard.c       | 8 ++++++++
> >  include/linux/mfd/viperboard.h | 2 +-
> >  2 files changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mfd/viperboard.c b/drivers/mfd/viperboard.c
> > index e00f534..5f62f4e 100644
> > --- a/drivers/mfd/viperboard.c
> > +++ b/drivers/mfd/viperboard.c
> > @@ -64,6 +64,12 @@ static int vprbrd_probe(struct usb_interface *interface,
> >  		return -ENOMEM;
> >  	}
> >  
> > +	vb->buf = kzalloc(sizeof(struct vprbrd_i2c_write_msg), GFP_KERNEL);
> > +	if (vb->buf == NULL) {
> > +		ret = -ENOMEM;
> > +		goto error;
> 
> This will cause a kref imbalance as you have a usb_put_dev in error,
> but haven't done the get yet.

Nevermind. This isn't problem as the usb device is null.

Haven't had my morning coffee yet. ;)

Johan
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