linux-kernel - Re: [PATCH v2 4/4] remoteproc: debugfs: Add ability to boot remote processor using debugfs

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Date:	Fri, 28 Aug 2015 10:23:14 -0500
From:	Nathan Lynch <Nathan_Lynch@...tor.com>
To:	Lee Jones <lee.jones@...aro.org>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <kernel@...inux.com>,
	<ohad@...ery.com>, <devicetree@...r.kernel.org>,
	Ludovic Barre <ludovic.barre@...com>
Subject: Re: [PATCH v2 4/4] remoteproc: debugfs: Add ability to boot remote
 processor using debugfs

On 08/28/2015 05:31 AM, Lee Jones wrote:
> +static ssize_t rproc_state_write(struct file *filp, const char __user *userbuf,
> +				 size_t count, loff_t *ppos)
> +{
> +	struct rproc *rproc = filp->private_data;
> +	char buf[2];
> +	int ret;
> +
> +	ret = copy_from_user(buf, userbuf, 1);
> +	if (ret)
> +		return -EFAULT;
> +
> +	switch (buf[0]) {
> +	case '0':
> +		rproc_shutdown(rproc);
> +		break;
> +	case '1':
> +		ret = rproc_boot(rproc);
> +		if (ret)
> +			dev_warn(&rproc->dev, "Boot failed: %d\n", ret);
> +		break;
> +	default:
> +		dev_err(&rproc->dev, "Unrecognised option: %x\n", buf[1]);
> +		return -EINVAL;

This prints uninitialized kernel stack contents instead of what was
copied from user space.

Is the dev_err statement really necessary anyway?

> +	}
> +
> +	return count;
> +}

If rproc_boot fails, that should be reflected in the syscall result.

This interface is essentially exposing the remoteproc->power refcount to
user space; is that okay?  Seems like it makes it easy to underflow
remoteproc->power through successive shutdown calls.

The other debugfs interface in remoteproc that has a write method
(recovery) accepts more expressive string commands as opposed to 0/1.
It would be more consistent for this interface to take commands such as
"boot" and "shutdown" IMO.

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