linux-kernel - Re: [RFC 7/7] [media] rc: add support for IR LEDs driven through SPI

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160721102208.GA1246@gofer.mess.org>
Date:	Thu, 21 Jul 2016 11:22:09 +0100
From:	Sean Young <sean@...s.org>
To:	Andi Shyti <andi.shyti@...sung.com>
Cc:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andi Shyti <andi@...zian.org>
Subject: Re: [RFC 7/7] [media] rc: add support for IR LEDs driven through SPI

Hi Andi,

On Thu, Jul 21, 2016 at 10:09:26AM +0900, Andi Shyti wrote:
> > > +	ret = regulator_enable(idata->regulator);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	mutex_lock(&idata->mutex);
> > > +	idata->xfer.len = n;
> > > +	idata->xfer.tx_buf = buffer;
> > > +	mutex_unlock(&idata->mutex);
> > 
> > I'm not convinced the locking works here. You want to guard against 
> > someone modifying xfer while you are sending (so in spi_sync_transfer), 
> > which this locking is not doing. You could declare a 
> > local "struct spi_transfer xfer" and avoid the mutex altogether.
> 
> I cannot declare xfer locally because the spi framework needs
> a statically allocated xfer, so that either I dynamically
> allocate it in the function or I declare it global in idata.

It can be stack allocated for sync transfers. You might want to lock
the spi bus.

> With the mutex I would like to prevent different tasks to change
> the value at the same time, it's an easy case, it shouldn't make
> much difference.

That's cargo-cult locking. It does not achieve anything.


Sean