RE: [PATCH 3/3] powerpc/fsl: add MPIC timer wakeup support

-----Original Message-----
From: Wood Scott-B07421
Sent: Wednesday, March 20, 2013 6:55 AM
To: Wang Dongsheng-B40534
Cc: Wood Scott-B07421; Gala Kumar-B11780; linuxppc-dev@lists.ozlabs.org;
Zhao Chenhui-B35336; Li Yang-R58472
Subject: Re: [PATCH 3/3] powerpc/fsl: add MPIC timer wakeup support
=20
On 03/19/2013 01:25:42 AM, Wang Dongsheng-B40534 wrote:

quoted

quoted

-----Original Message-----
From: Wood Scott-B07421
Sent: Tuesday, March 19, 2013 8:31 AM
To: Wang Dongsheng-B40534
Cc: Gala Kumar-B11780; linuxppc-dev@lists.ozlabs.org; Wang

Dongsheng-

quoted

B40534; Zhao Chenhui-B35336; Li Yang-R58472
Subject: Re: [PATCH 3/3] powerpc/fsl: add MPIC timer wakeup support

On 03/08/2013 01:38:47 AM, Wang Dongsheng wrote:

quoted

+static ssize_t fsl_timer_wakeup_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf,
+				size_t count)
+{
+	struct timeval interval;
+	int ret;
+
+	interval.tv_usec =3D 0;
+	if (kstrtol(buf, 0, &interval.tv_sec))
+		return -EINVAL;

I don't think the buffer will NUL-terminated...  Ordinarily

there'll be

quoted

an LF terminator, but you can't rely on that (many other sysfs

attributes

quoted

seem to, though...).

I think we don't need to care about LF terminator.
The kstrtol--> _kstrtoull has been done.

=20
My point is, what happens if userspace passes in a buffer that has no
terminator of any sort?  kstrtol will continue reading beyond the end of
the buffer.
=20

Do not care about terminator.

kstrtol--> _kstrtoull--> _parse_integer

_kstrtoull(...) {
	...
	rv =3D _parse_integer(s, base, &_res);
	if (rv & KSTRTOX_OVERFLOW)
		return -ERANGE;
	rv &=3D ~KSTRTOX_OVERFLOW;
	if (rv =3D=3D 0)
		return -EINVAL;
	s +=3D rv;

	if (*s =3D=3D '\n')
		s++;
	if (*s)
		return -EINVAL;
	...
}

_parse_integer(...) {
	...
	while (*s) {
		if ('0' <=3D *s && *s <=3D '9')
			val =3D *s - '0';
		else if ('a' <=3D _tolower(*s) && _tolower(*s) <=3D 'f')
			val =3D _tolower(*s) - 'a' + 10;
		else
			break;	//this will break out to convert.

		if (val >=3D base)
			break;
	}
	...
}

quoted

quoted

quoted

+	mutex_lock(&sysfs_lock);
+
+	if (fsl_wakeup->timer && !interval.tv_sec) {
+		disable_irq_wake(fsl_wakeup->timer->irq);
+		mpic_free_timer(fsl_wakeup->timer);
+		fsl_wakeup->timer =3D NULL;
+		mutex_unlock(&sysfs_lock);
+
+		return count;
+	}
+
+	if (fsl_wakeup->timer) {
+		mutex_unlock(&sysfs_lock);
+		return -EBUSY;
+	}

So to change an already-set timer you have to set it to zero and

then to

quoted

what you want?  Why not just do:

	if (fsl_wakeup->timer) {
		disable_irq_wake(...);
		mpic_free_timer(...);
		fsl_wakeup_timer =3D NULL;
	}

	if (!interval.tv_sec) {
		mutex_unlock(&sysfs_lock);
		return count;
	}

You can't break up the it.
if echo zero the code will cancel the timer that is currently running.
Not echo non-zero value just zero to cancel.

=20
Echoing a nonzero value wouldn't just be to cancel, it would be to set a
new timer after cancelling the old.
=20

If you think this way is better, I can change.
But why should do it?=20
Explicitly stop the timer (echo 0) before reuse it is more reasonable for m=
e.=20

quoted

quoted

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+	for (i =3D 0; mpic_attributes[i]; i++) {
+		ret =3D device_create_file(mpic_subsys.dev_root,
+					mpic_attributes[i]);
+		if (ret)
+			goto err2;
+	}

Is this code ever going to register more than one?

No, just one. I only keep the style here.
If you don't think it's necessary I can remove this loop.

=20
I don't think it's necessary.
=20

Ok, I will remove this loop.