Re: [PATCH v4 3/4] PM / devfreq: Rework freq_table to be local to devfreq struct

[Christian Marangi]

On Sat, Jun 18, 2022 at 04:33:19AM +0900, Chanwoo Choi wrote:
> Hi,
> 
> Thanks for the good catch. 
> 
> 
> I think that this patch fixes issue of commit 0ec09ac2cebe
> ("PM / devfreq: Set the freq_table of devfreq device").
>

Should I add this to the Fixes list?

> When some devfreq driver without using passive governor
> faces on the all errors including PROBE_DEFER
> after executing devfreq_add_device, this issue will happen.
> 
> Also need to check the devfreq device driver using freq_table
> which was allocated dynamically. In case of devfreq/drivers/exynos-bus.c
> used the devfreq->profile->freq_table after devfreq_add_device.
> 
> On 22. 6. 15. 08:09, Christian 'Ansuel' Marangi wrote:
> > Currently we reference the freq_table to the profile defined one and we
> > make changes on it. Devfreq never supported PROBE_DEFER before the cpu
> > based scaling support to the passive governor and assumed that a devfreq
> > device could only had error and be done with it.
> > Now that a device can PROBE_DEFER a rework to the freq_table logic is
> > required.
> > 
> > If a device PROBE_DEFER on the GOV_START, the freq_table is already set
> > in the device profile struct and its init is skipped. This is due to the
> > fact that it's common for devs to declare this kind of struct static.
> > This cause the devfreq logic to find a freq table declared (freq_table
> > not NULL) with random data and poiting to the old addrs freed by devm.
>  > This problem CAN be solved by devs by clearing the freq_table in their
> > profile struct on driver exit path but it should not be trusted and it
> > looks to use a flawed logic.
> > 
> > A better solution is to move the freq_table and max_state to the
> > devfreq struct and never change the profile struct.
> > This permit to correctly handle PROBE_DEFER since the devfreq struct is
> > reallocated and contains new values.
> > Also the profile struct should only be used to init the driver and should
> > not be used by the devfreq to write the freq_table if it's not provided
> > by the driver.
> > 
> 
> If possible, could you explain the patch description more simply?
> Maybe, just focus on the 'freq_table' issue by device managed functions (devs).
>

Sure!

> 
> > Fixes: a03dacb0316f ("PM / devfreq: Add cpu based scaling support to passive governor")
> > Signed-off-by: Christian 'Ansuel' Marangi <ansuelsmth@xxxxxxxxx>
> > ---
> >  drivers/devfreq/devfreq.c          | 71 ++++++++++++++----------------
> >  drivers/devfreq/governor_passive.c | 14 +++---
> >  include/linux/devfreq.h            |  4 ++
> >  3 files changed, 45 insertions(+), 44 deletions(-)
> > 
> > diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> > index 01474daf4548..2e2b3b414d67 100644
> > --- a/drivers/devfreq/devfreq.c
> > +++ b/drivers/devfreq/devfreq.c
> > @@ -123,7 +123,7 @@ void devfreq_get_freq_range(struct devfreq *devfreq,
> >  			    unsigned long *min_freq,
> >  			    unsigned long *max_freq)
> >  {
> > -	unsigned long *freq_table = devfreq->profile->freq_table;
> > +	unsigned long *freq_table = devfreq->freq_table;
> >  	s32 qos_min_freq, qos_max_freq;
> >  
> >  	lockdep_assert_held(&devfreq->lock);
> > @@ -133,11 +133,11 @@ void devfreq_get_freq_range(struct devfreq *devfreq,
> >  	 * The devfreq drivers can initialize this in either ascending or
> >  	 * descending order and devfreq core supports both.
> >  	 */
> > -	if (freq_table[0] < freq_table[devfreq->profile->max_state - 1]) {
> > +	if (freq_table[0] < freq_table[devfreq->max_state - 1]) {
> >  		*min_freq = freq_table[0];
> > -		*max_freq = freq_table[devfreq->profile->max_state - 1];
> > +		*max_freq = freq_table[devfreq->max_state - 1];
> >  	} else {
> > -		*min_freq = freq_table[devfreq->profile->max_state - 1];
> > +		*min_freq = freq_table[devfreq->max_state - 1];
> >  		*max_freq = freq_table[0];
> >  	}
> >  
> > @@ -169,8 +169,8 @@ static int devfreq_get_freq_level(struct devfreq *devfreq, unsigned long freq)
> >  {
> >  	int lev;
> >  
> > -	for (lev = 0; lev < devfreq->profile->max_state; lev++)
> > -		if (freq == devfreq->profile->freq_table[lev])
> > +	for (lev = 0; lev < devfreq->max_state; lev++)
> > +		if (freq == devfreq->freq_table[lev])
> >  			return lev;
> >  
> >  	return -EINVAL;
> > @@ -178,7 +178,6 @@ static int devfreq_get_freq_level(struct devfreq *devfreq, unsigned long freq)
> >  
> >  static int set_freq_table(struct devfreq *devfreq)
> >  {
> > -	struct devfreq_dev_profile *profile = devfreq->profile;
> >  	struct dev_pm_opp *opp;
> >  	unsigned long freq;
> >  	int i, count;
> > @@ -188,25 +187,22 @@ static int set_freq_table(struct devfreq *devfreq)
> >  	if (count <= 0)
> >  		return -EINVAL;
> >  
> > -	profile->max_state = count;
> > -	profile->freq_table = devm_kcalloc(devfreq->dev.parent,
> > -					profile->max_state,
> > -					sizeof(*profile->freq_table),
> > -					GFP_KERNEL);
> > -	if (!profile->freq_table) {
> > -		profile->max_state = 0;
> > +	devfreq->max_state = count;
> > +	devfreq->freq_table = devm_kcalloc(devfreq->dev.parent,
> > +					   devfreq->max_state,
> > +					   sizeof(*devfreq->freq_table),
> > +					   GFP_KERNEL);
> > +	if (!devfreq->freq_table)
> >  		return -ENOMEM;
> > -	}
> >  
> > -	for (i = 0, freq = 0; i < profile->max_state; i++, freq++) {
> > +	for (i = 0, freq = 0; i < devfreq->max_state; i++, freq++) {
> >  		opp = dev_pm_opp_find_freq_ceil(devfreq->dev.parent, &freq);
> >  		if (IS_ERR(opp)) {
> > -			devm_kfree(devfreq->dev.parent, profile->freq_table);
> > -			profile->max_state = 0;
> > +			devm_kfree(devfreq->dev.parent, devfreq->freq_table);
> >  			return PTR_ERR(opp);
> >  		}
> >  		dev_pm_opp_put(opp);
> > -		profile->freq_table[i] = freq;
> > +		devfreq->freq_table[i] = freq;
> >  	}
> >  
> >  	return 0;
> > @@ -246,7 +242,7 @@ int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
> >  
> >  	if (lev != prev_lev) {
> >  		devfreq->stats.trans_table[
> > -			(prev_lev * devfreq->profile->max_state) + lev]++;
> > +			(prev_lev * devfreq->max_state) + lev]++;
> >  		devfreq->stats.total_trans++;
> >  	}
> >  
> > @@ -835,6 +831,9 @@ struct devfreq *devfreq_add_device(struct device *dev,
> >  		if (err < 0)
> >  			goto err_dev;
> >  		mutex_lock(&devfreq->lock);
> > +	} else {
> > +		devfreq->freq_table = devfreq->profile->freq_table;
> > +		devfreq->max_state = devfreq->profile->max_state;
> >  	}
> >  
> >  	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
> > @@ -870,8 +869,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
> >  
> >  	devfreq->stats.trans_table = devm_kzalloc(&devfreq->dev,
> >  			array3_size(sizeof(unsigned int),
> > -				    devfreq->profile->max_state,
> > -				    devfreq->profile->max_state),
> > +				    devfreq->max_state,
> > +				    devfreq->max_state),
> >  			GFP_KERNEL);
> >  	if (!devfreq->stats.trans_table) {
> >  		mutex_unlock(&devfreq->lock);
> > @@ -880,7 +879,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
> >  	}
> >  
> >  	devfreq->stats.time_in_state = devm_kcalloc(&devfreq->dev,
> > -			devfreq->profile->max_state,
> > +			devfreq->max_state,
> >  			sizeof(*devfreq->stats.time_in_state),
> >  			GFP_KERNEL);
> >  	if (!devfreq->stats.time_in_state) {
> > @@ -1665,9 +1664,9 @@ static ssize_t available_frequencies_show(struct device *d,
> >  
> >  	mutex_lock(&df->lock);
> >  
> > -	for (i = 0; i < df->profile->max_state; i++)
> > +	for (i = 0; i < df->max_state; i++)
> >  		count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
> > -				"%lu ", df->profile->freq_table[i]);
> > +				"%lu ", df->freq_table[i]);
> >  
> >  	mutex_unlock(&df->lock);
> >  	/* Truncate the trailing space */
> > @@ -1690,7 +1689,7 @@ static ssize_t trans_stat_show(struct device *dev,
> >  
> >  	if (!df->profile)
> >  		return -EINVAL;
> > -	max_state = df->profile->max_state;
> > +	max_state = df->max_state;
> >  
> >  	if (max_state == 0)
> >  		return sprintf(buf, "Not Supported.\n");
> > @@ -1707,19 +1706,17 @@ static ssize_t trans_stat_show(struct device *dev,
> >  	len += sprintf(buf + len, "           :");
> >  	for (i = 0; i < max_state; i++)
> >  		len += sprintf(buf + len, "%10lu",
> > -				df->profile->freq_table[i]);
> > +				df->freq_table[i]);
> >  
> >  	len += sprintf(buf + len, "   time(ms)\n");
> >  
> >  	for (i = 0; i < max_state; i++) {
> > -		if (df->profile->freq_table[i]
> > -					== df->previous_freq) {
> > +		if (df->freq_table[i] == df->previous_freq)
> >  			len += sprintf(buf + len, "*");
> > -		} else {
> > +		else
> >  			len += sprintf(buf + len, " ");
> > -		}
> > -		len += sprintf(buf + len, "%10lu:",
> > -				df->profile->freq_table[i]);
> > +
> > +		len += sprintf(buf + len, "%10lu:", df->freq_table[i]);
> >  		for (j = 0; j < max_state; j++)
> >  			len += sprintf(buf + len, "%10u",
> >  				df->stats.trans_table[(i * max_state) + j]);
> > @@ -1743,7 +1740,7 @@ static ssize_t trans_stat_store(struct device *dev,
> >  	if (!df->profile)
> >  		return -EINVAL;
> >  
> > -	if (df->profile->max_state == 0)
> > +	if (df->max_state == 0)
> >  		return count;
> >  
> >  	err = kstrtoint(buf, 10, &value);
> > @@ -1751,11 +1748,11 @@ static ssize_t trans_stat_store(struct device *dev,
> >  		return -EINVAL;
> >  
> >  	mutex_lock(&df->lock);
> > -	memset(df->stats.time_in_state, 0, (df->profile->max_state *
> > +	memset(df->stats.time_in_state, 0, (df->max_state *
> >  					sizeof(*df->stats.time_in_state)));
> >  	memset(df->stats.trans_table, 0, array3_size(sizeof(unsigned int),
> > -					df->profile->max_state,
> > -					df->profile->max_state));
> > +					df->max_state,
> > +					df->max_state));
> >  	df->stats.total_trans = 0;
> >  	df->stats.last_update = get_jiffies_64();
> >  	mutex_unlock(&df->lock);
> > diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
> > index dcc9dd518197..1810966fd61d 100644
> > --- a/drivers/devfreq/governor_passive.c
> > +++ b/drivers/devfreq/governor_passive.c
> > @@ -145,18 +145,18 @@ static int get_target_freq_with_devfreq(struct devfreq *devfreq,
> >  		goto out;
> >  
> >  	/* Use interpolation if required opps is not available */
> > -	for (i = 0; i < parent_devfreq->profile->max_state; i++)
> > -		if (parent_devfreq->profile->freq_table[i] == *freq)
> > +	for (i = 0; i < parent_devfreq->max_state; i++)
> > +		if (parent_devfreq->freq_table[i] == *freq)
> >  			break;
> >  
> > -	if (i == parent_devfreq->profile->max_state)
> > +	if (i == parent_devfreq->max_state)
> >  		return -EINVAL;
> >  
> > -	if (i < devfreq->profile->max_state) {
> > -		child_freq = devfreq->profile->freq_table[i];
> > +	if (i < devfreq->max_state) {
> > +		child_freq = devfreq->freq_table[i];
> >  	} else {
> > -		count = devfreq->profile->max_state;
> > -		child_freq = devfreq->profile->freq_table[count - 1];
> > +		count = devfreq->max_state;
> > +		child_freq = devfreq->freq_table[count - 1];
> >  	}
> >  
> >  out:
> > diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> > index dc10bee75a72..770a7532655c 100644
> > --- a/include/linux/devfreq.h
> > +++ b/include/linux/devfreq.h
> > @@ -185,6 +185,10 @@ struct devfreq {
> >  	struct notifier_block nb;
> >  	struct delayed_work work;
> >  
> > +	/* devfreq local freq_table */
> > +	unsigned long *freq_table;
> > +	unsigned int max_state;
> > +
> >  	unsigned long previous_freq;
> >  	struct devfreq_dev_status last_status;
> >  
> 
> 
> -- 
> Best Regards,
> Samsung Electronics
> Chanwoo Choi

-- 
	Ansuel