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

From: Marek Szyprowski
Date: Fri Jul 01 2022 - 04:02:12 EST

Hi All,

On 20.06.2022 00:03, Christian Marangi wrote:
> On a devfreq PROBE_DEFER, the freq_table in the driver profile struct,
> is never reset and may be leaved in an undefined state.
>
> This comes from the fact that we store the freq_table in the driver
> profile struct that is commonly defined as static and not reset on
> PROBE_DEFER.
> We currently skip the reinit of the freq_table if we found
> it's already defined since a driver may declare his own freq_table.
>
> This logic is flawed in the case devfreq core generate a freq_table, set
> it in the profile struct and then PROBE_DEFER, freeing the freq_table.
> In this case devfreq will found a NOT NULL freq_table that has been
> freed, skip the freq_table generation and probe the driver based on the
> wrong table.
>
> To fix this and correctly handle PROBE_DEFER, use a local freq_table and
> max_state in the devfreq struct and never modify the freq_table present
> in the profile struct if it does provide it.
>
> Fixes: 0ec09ac2cebe ("PM / devfreq: Set the freq_table of devfreq device")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Christian Marangi <ansuelsmth@xxxxxxxxx>
> ---

This patch landed in linux next-20220630 as commit b5d281f6c16d ("PM /
devfreq: Rework freq_table to be local to devfreq struct").
Unfortunately it causes the following regression on my Exynos based test
systems:

8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 00000000
[00000000] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 3 PID: 49 Comm: kworker/u8:3 Not tainted 5.19.0-rc4-next-20220630 #5312
Hardware name: Samsung Exynos (Flattened Device Tree)
Workqueue: events_unbound deferred_probe_work_func
PC is at exynos_bus_probe+0x604/0x684
LR is at device_add+0x14c/0x908
pc : [<c090aef4>]    lr : [<c06cf77c>]    psr: 80000053
...
Process kworker/u8:3 (pid: 49, stack limit = 0x(ptrval))
Stack: (0xf0a15d30 to 0xf0a16000)
...
 exynos_bus_probe from platform_probe+0x5c/0xb8
 platform_probe from really_probe+0xe0/0x414
 really_probe from __driver_probe_device+0xa0/0x208
 __driver_probe_device from driver_probe_device+0x30/0xc0
 driver_probe_device from __device_attach_driver+0xa4/0x11c
 __device_attach_driver from bus_for_each_drv+0x7c/0xc0
 bus_for_each_drv from __device_attach+0xac/0x20c
 __device_attach from bus_probe_device+0x88/0x90
 bus_probe_device from deferred_probe_work_func+0x98/0xe0
 deferred_probe_work_func from process_one_work+0x288/0x774
 process_one_work from worker_thread+0x44/0x504
 worker_thread from kthread+0xf4/0x128
 kthread from ret_from_fork+0x14/0x2c
Exception stack(0xf0a15fb0 to 0xf0a15ff8)
...
---[ end trace 0000000000000000 ]---

This issue is caused by bus->devfreq->profile->freq_table being NULL here:

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/devfreq/exynos-bus.c?h=next-20220630#n451


> drivers/devfreq/devfreq.c | 71 ++++++++++++++----------------
> drivers/devfreq/governor_passive.c | 14 +++---
> include/linux/devfreq.h | 5 +++
> 3 files changed, 46 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 72c67979ebe1..ce24a262aa16 100644
> --- a/drivers/devfreq/governor_passive.c
> +++ b/drivers/devfreq/governor_passive.c
> @@ -131,18 +131,18 @@ 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..34aab4dd336c 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -148,6 +148,8 @@ struct devfreq_stats {
> * reevaluate operable frequencies. Devfreq users may use
> * devfreq.nb to the corresponding register notifier call chain.
> * @work: delayed work for load monitoring.
> + * @freq_table: current frequency table used by the devfreq driver.
> + * @max_state: count of entry present in the frequency table.
> * @previous_freq: previously configured frequency value.
> * @last_status: devfreq user device info, performance statistics
> * @data: Private data of the governor. The devfreq framework does not
> @@ -185,6 +187,9 @@ struct devfreq {
> struct notifier_block nb;
> struct delayed_work work;
>
> + unsigned long *freq_table;
> + unsigned int max_state;
> +
> unsigned long previous_freq;
> struct devfreq_dev_status last_status;
>

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland