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

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Date:	Wed, 24 Sep 2014 15:34:08 +0300
From:	Octavian Purdila <octavian.purdila@...el.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	Lee Jones <lee.jones@...aro.org>,
	lkml <linux-kernel@...r.kernel.org>, linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 1/2] mfd: viperboard: allocate I/O buffer separately

On Wed, Sep 24, 2014 at 3:26 PM, Johan Hovold <johan@...nel.org> wrote:
> On Wed, Sep 24, 2014 at 01:00:02PM +0100, Lee Jones wrote:
>> On Wed, 24 Sep 2014, Johan Hovold wrote:
>>
>> > On Wed, Sep 24, 2014 at 11:12:06AM +0100, Lee Jones wrote:
>> > > On Mon, 22 Sep 2014, 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);
>> > >
>> > > Can you obtain the 'struct device' first then use managed resources
>> > > (devm_*)?
>> >
>> > I think any devres conversion should be done in a follow-up patch and
>> > not be included in the fix (e.g. in order to facilitate backporting). We
>> > also don't want to mix allocation schemes.
>>
>> I agree, but equally I'm not keen on accepting this patch as I believe
>> it could be done better.
>>
>> Please submit two patches, one converting to shared resources and this
>> being the subsequent one, fixed up to do the right thing.
>
> A buffer-corruption fix is a candidate for stable, whereas a devres
> conversion (clean up) is not. Hence the former should not depend on the
> latter.
>

I can follow-up with a v3 3 patch series: first for the fix, second
for the OOM & error path cleanup, third for devm conversion.

I think this will address both issues (backport and better final result).
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