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

From: Chanwoo Choi
Date: Fri Jun 17 2022 - 15:33:41 EST


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").

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).


> 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