drivers/cpufreq/cpufreq.c | 32 +++++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-)
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Since cpufreq_driver_resolve_freq() can run in parallel with
cpufreq_set_policy() and there is no synchronization between them,
the former may access policy->min and policy->max while the latter
is updating them and it may see intermediate values of them due
to the way the update is carried out. Also the compiler is free
to apply any optimizations it wants both to the stores in
cpufreq_set_policy() and to the loads in cpufreq_driver_resolve_freq()
which may result in additional inconsistencies.
To address this, use WRITE_ONCE() when updating policy->min and
policy->max in cpufreq_set_policy() and use READ_ONCE() for reading
them in cpufreq_driver_resolve_freq(). Moreover, rearrange the update
in cpufreq_set_policy() to avoid storing intermediate values in
policy->min and policy->max with the help of the observation that
their new values are expected to be properly ordered upfront.
Also modify cpufreq_driver_resolve_freq() to take the possible reverse
ordering of policy->min and policy->max, which may happen depending on
the ordering of operations when this function and cpufreq_set_policy()
run concurrently, into account by always honoring the max when it
turns out to be less than the min (in case it comes from thermal
throttling or similar).
Fixes: 151717690694 ("cpufreq: Make policy min/max hard requirements")
Cc: 5.16+ <stable@vger.kernel.org> # 5.16+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
This replaces the last 3 patches in
https://lore.kernel.org/linux-pm/6171293.lOV4Wx5bFT@rjwysocki.net/
v2 -> v3:
* Fold 3 patches into one.
* Drop an unrelated white space fixup change.
* Fix a typo in a comment (Christian).
v1 -> v2: Cosmetic changes
---
drivers/cpufreq/cpufreq.c | 32 +++++++++++++++++++++++++-------
1 file changed, 25 insertions(+), 7 deletions(-)
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -495,8 +495,6 @@
{
unsigned int idx;
- target_freq = clamp_val(target_freq, policy->min, policy->max);
-
if (!policy->freq_table)
return target_freq;
@@ -520,7 +518,22 @@
unsigned int cpufreq_driver_resolve_freq(struct cpufreq_policy *policy,
unsigned int target_freq)
{
- return __resolve_freq(policy, target_freq, CPUFREQ_RELATION_LE);
+ unsigned int min = READ_ONCE(policy->min);
+ unsigned int max = READ_ONCE(policy->max);
+
+ /*
+ * If this function runs in parallel with cpufreq_set_policy(), it may
+ * read policy->min before the update and policy->max after the update
+ * or the other way around, so there is no ordering guarantee.
+ *
+ * Resolve this by always honoring the max (in case it comes from
+ * thermal throttling or similar).
+ */
+ if (unlikely(min > max))
+ min = max;
+
+ return __resolve_freq(policy, clamp_val(target_freq, min, max),
+ CPUFREQ_RELATION_LE);
}
EXPORT_SYMBOL_GPL(cpufreq_driver_resolve_freq);
@@ -2338,6 +2351,7 @@
if (cpufreq_disabled())
return -ENODEV;
+ target_freq = clamp_val(target_freq, policy->min, policy->max);
target_freq = __resolve_freq(policy, target_freq, relation);
pr_debug("target for CPU %u: %u kHz, relation %u, requested %u kHz\n",
@@ -2631,11 +2645,15 @@
* Resolve policy min/max to available frequencies. It ensures
* no frequency resolution will neither overshoot the requested maximum
* nor undershoot the requested minimum.
+ *
+ * Avoid storing intermediate values in policy->max or policy->min and
+ * compiler optimizations around them because they may be accessed
+ * concurrently by cpufreq_driver_resolve_freq() during the update.
*/
- policy->min = new_data.min;
- policy->max = new_data.max;
- policy->min = __resolve_freq(policy, policy->min, CPUFREQ_RELATION_L);
- policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
+ WRITE_ONCE(policy->max, __resolve_freq(policy, new_data.max, CPUFREQ_RELATION_H));
+ new_data.min = __resolve_freq(policy, new_data.min, CPUFREQ_RELATION_L);
+ WRITE_ONCE(policy->min, new_data.min > policy->max ? policy->max : new_data.min);
+
trace_cpu_frequency_limits(policy);
cpufreq_update_pressure(policy);Hi Rafael,
On Wed, Apr 16, 2025 at 04:12:37PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Since cpufreq_driver_resolve_freq() can run in parallel with
> cpufreq_set_policy() and there is no synchronization between them,
> the former may access policy->min and policy->max while the latter
> is updating them and it may see intermediate values of them due
> to the way the update is carried out. Also the compiler is free
> to apply any optimizations it wants both to the stores in
> cpufreq_set_policy() and to the loads in cpufreq_driver_resolve_freq()
> which may result in additional inconsistencies.
>
> To address this, use WRITE_ONCE() when updating policy->min and
> policy->max in cpufreq_set_policy() and use READ_ONCE() for reading
> them in cpufreq_driver_resolve_freq(). Moreover, rearrange the update
> in cpufreq_set_policy() to avoid storing intermediate values in
> policy->min and policy->max with the help of the observation that
> their new values are expected to be properly ordered upfront.
>
> Also modify cpufreq_driver_resolve_freq() to take the possible reverse
> ordering of policy->min and policy->max, which may happen depending on
> the ordering of operations when this function and cpufreq_set_policy()
> run concurrently, into account by always honoring the max when it
> turns out to be less than the min (in case it comes from thermal
> throttling or similar).
>
> Fixes: 151717690694 ("cpufreq: Make policy min/max hard requirements")
> Cc: 5.16+ <stable@vger.kernel.org> # 5.16+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>
> This replaces the last 3 patches in
>
> https://lore.kernel.org/linux-pm/6171293.lOV4Wx5bFT@rjwysocki.net/
>
> v2 -> v3:
> * Fold 3 patches into one.
> * Drop an unrelated white space fixup change.
> * Fix a typo in a comment (Christian).
>
> v1 -> v2: Cosmetic changes
>
> ---
> drivers/cpufreq/cpufreq.c | 32 +++++++++++++++++++++++++-------
> 1 file changed, 25 insertions(+), 7 deletions(-)
>
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -495,8 +495,6 @@
> {
> unsigned int idx;
>
> - target_freq = clamp_val(target_freq, policy->min, policy->max);
> -
> if (!policy->freq_table)
> return target_freq;
>
> @@ -520,7 +518,22 @@
> unsigned int cpufreq_driver_resolve_freq(struct cpufreq_policy *policy,
> unsigned int target_freq)
> {
> - return __resolve_freq(policy, target_freq, CPUFREQ_RELATION_LE);
> + unsigned int min = READ_ONCE(policy->min);
> + unsigned int max = READ_ONCE(policy->max);
> +
> + /*
> + * If this function runs in parallel with cpufreq_set_policy(), it may
> + * read policy->min before the update and policy->max after the update
> + * or the other way around, so there is no ordering guarantee.
> + *
> + * Resolve this by always honoring the max (in case it comes from
> + * thermal throttling or similar).
> + */
> + if (unlikely(min > max))
> + min = max;
> +
> + return __resolve_freq(policy, clamp_val(target_freq, min, max),
> + CPUFREQ_RELATION_LE);
> }
> EXPORT_SYMBOL_GPL(cpufreq_driver_resolve_freq);
>
> @@ -2338,6 +2351,7 @@
> if (cpufreq_disabled())
> return -ENODEV;
>
> + target_freq = clamp_val(target_freq, policy->min, policy->max);
> target_freq = __resolve_freq(policy, target_freq, relation);
>
> pr_debug("target for CPU %u: %u kHz, relation %u, requested %u kHz\n",
> @@ -2631,11 +2645,15 @@
> * Resolve policy min/max to available frequencies. It ensures
> * no frequency resolution will neither overshoot the requested maximum
> * nor undershoot the requested minimum.
> + *
> + * Avoid storing intermediate values in policy->max or policy->min and
> + * compiler optimizations around them because they may be accessed
> + * concurrently by cpufreq_driver_resolve_freq() during the update.
> */
> - policy->min = new_data.min;
> - policy->max = new_data.max;
> - policy->min = __resolve_freq(policy, policy->min, CPUFREQ_RELATION_L);
> - policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
> + WRITE_ONCE(policy->max, __resolve_freq(policy, new_data.max, CPUFREQ_RELATION_H));
> + new_data.min = __resolve_freq(policy, new_data.min, CPUFREQ_RELATION_L);
> + WRITE_ONCE(policy->min, new_data.min > policy->max ? policy->max : new_data.min);
I've tested the cpufreq throttling again in 6.15-rc3 to check your fix
for the schedutil CPUFREQ_NEED_UPDATE_LIMITS regression I reported [1].
The CPU frequency is now being throttled correctly when reaching high
temperatures. Thanks for fixing this!
Unfortunately, the opposite case has now regressed with this patch:
After the CPU frequency has been throttled due to high temperature and
the device cools down again, the CPU frequency is stuck at minimum until
you reboot. policy->max will never restore to the maximum frequency.
I've confirmed that this causes unexpected slowness after temperature
throttling on a Qualcomm X1E laptop, and Johan has confirmed that e.g.
the ThinkPad X13s is also affected. I would expect that most devices
using cpufreq cooling in the kernel are affected.
Looking at the code, I think the problem is that __resolve_freq() ->
cpufreq_frequency_table_target() -> cpufreq_table_find_index*() and
cpufreq_is_in_limits() are still using the old policy->min/max value.
In this patch, you have only moved the clamp_val() usage directly in
__resolve_freq().
You can see this in the following debug log. I started a stress test
that increases the device temperature until the CPU frequency was
throttled to minimum. Then I stopped the stress test, the device cooled
down, cpufreq_set_policy() was called with the new max frequency, but
__resolve_freq() still returned the frequency clamped to the old maximum.
[ 149.959693] cpufreq: handle_update for cpu 0 called
[ 149.964782] cpufreq: updating policy for CPU 0
[ 149.969411] cpufreq: setting new policy for CPU 0: 0 - 3206400 kHz
[ 149.975842] cpufreq: new min and max freqs are 710400 - 3206400 kHz
[ 149.982347] cpufreq: governor limits update
[ 149.986715] cpufreq: cpufreq_governor_limits: for CPU 0
[...]
[ 161.219209] cpufreq: handle_update for cpu 0 called
[ 161.224291] cpufreq: updating policy for CPU 0
[ 161.228927] cpufreq: setting new policy for CPU 0: 0 - 710400 kHz
[ 161.235238] cpufreq: new min and max freqs are 710400 - 710400 kHz
[ 161.241635] cpufreq: governor limits update
[ 161.245989] cpufreq: cpufreq_governor_limits: for CPU 0
[ 221.253253] cpufreq: handle_update for cpu 0 called
[ 221.258322] cpufreq: updating policy for CPU 0
[ 221.262946] cpufreq: setting new policy for CPU 0: 0 - 3417600 kHz
[ 221.269418] cpufreq: new min and max freqs are 710400 - 710400 kHz
^ here the new maximum is not being applied
[ 221.275839] cpufreq: governor limits update
[ 221.280195] cpufreq: cpufreq_governor_limits: for CPU 0
Any thoughts how to fix this properly?
Please Cc me if you send a patch with the fix. The Reported-by: tag from
me on the fix for the CPUFREQ_NEED_UPDATE_LIMITS problem didn't Cc me
when sending for some reason, so I only learned about your fix when Greg
sent out the stable backports yesterday. :-)
Thanks,
Stephan
[1]: https://lore.kernel.org/lkml/Z_Tlc6Qs-tYpxWYb@linaro.org/
#regzbot introduced: 7491cdf46b5cbdf123fc84fbe0a07e9e3d7b7620
Hi,
On Thu, Apr 24, 2025 at 6:21 PM Stephan Gerhold
<stephan.gerhold@linaro.org> wrote:
>
> Hi Rafael,
>
> On Wed, Apr 16, 2025 at 04:12:37PM +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > Since cpufreq_driver_resolve_freq() can run in parallel with
> > cpufreq_set_policy() and there is no synchronization between them,
> > the former may access policy->min and policy->max while the latter
> > is updating them and it may see intermediate values of them due
> > to the way the update is carried out. Also the compiler is free
> > to apply any optimizations it wants both to the stores in
> > cpufreq_set_policy() and to the loads in cpufreq_driver_resolve_freq()
> > which may result in additional inconsistencies.
> >
> > To address this, use WRITE_ONCE() when updating policy->min and
> > policy->max in cpufreq_set_policy() and use READ_ONCE() for reading
> > them in cpufreq_driver_resolve_freq(). Moreover, rearrange the update
> > in cpufreq_set_policy() to avoid storing intermediate values in
> > policy->min and policy->max with the help of the observation that
> > their new values are expected to be properly ordered upfront.
> >
> > Also modify cpufreq_driver_resolve_freq() to take the possible reverse
> > ordering of policy->min and policy->max, which may happen depending on
> > the ordering of operations when this function and cpufreq_set_policy()
> > run concurrently, into account by always honoring the max when it
> > turns out to be less than the min (in case it comes from thermal
> > throttling or similar).
> >
> > Fixes: 151717690694 ("cpufreq: Make policy min/max hard requirements")
> > Cc: 5.16+ <stable@vger.kernel.org> # 5.16+
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >
> > This replaces the last 3 patches in
> >
> > https://lore.kernel.org/linux-pm/6171293.lOV4Wx5bFT@rjwysocki.net/
> >
> > v2 -> v3:
> > * Fold 3 patches into one.
> > * Drop an unrelated white space fixup change.
> > * Fix a typo in a comment (Christian).
> >
> > v1 -> v2: Cosmetic changes
> >
> > ---
> > drivers/cpufreq/cpufreq.c | 32 +++++++++++++++++++++++++-------
> > 1 file changed, 25 insertions(+), 7 deletions(-)
> >
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -495,8 +495,6 @@
> > {
> > unsigned int idx;
> >
> > - target_freq = clamp_val(target_freq, policy->min, policy->max);
> > -
> > if (!policy->freq_table)
> > return target_freq;
> >
> > @@ -520,7 +518,22 @@
> > unsigned int cpufreq_driver_resolve_freq(struct cpufreq_policy *policy,
> > unsigned int target_freq)
> > {
> > - return __resolve_freq(policy, target_freq, CPUFREQ_RELATION_LE);
> > + unsigned int min = READ_ONCE(policy->min);
> > + unsigned int max = READ_ONCE(policy->max);
> > +
> > + /*
> > + * If this function runs in parallel with cpufreq_set_policy(), it may
> > + * read policy->min before the update and policy->max after the update
> > + * or the other way around, so there is no ordering guarantee.
> > + *
> > + * Resolve this by always honoring the max (in case it comes from
> > + * thermal throttling or similar).
> > + */
> > + if (unlikely(min > max))
> > + min = max;
> > +
> > + return __resolve_freq(policy, clamp_val(target_freq, min, max),
> > + CPUFREQ_RELATION_LE);
> > }
> > EXPORT_SYMBOL_GPL(cpufreq_driver_resolve_freq);
> >
> > @@ -2338,6 +2351,7 @@
> > if (cpufreq_disabled())
> > return -ENODEV;
> >
> > + target_freq = clamp_val(target_freq, policy->min, policy->max);
> > target_freq = __resolve_freq(policy, target_freq, relation);
> >
> > pr_debug("target for CPU %u: %u kHz, relation %u, requested %u kHz\n",
> > @@ -2631,11 +2645,15 @@
> > * Resolve policy min/max to available frequencies. It ensures
> > * no frequency resolution will neither overshoot the requested maximum
> > * nor undershoot the requested minimum.
> > + *
> > + * Avoid storing intermediate values in policy->max or policy->min and
> > + * compiler optimizations around them because they may be accessed
> > + * concurrently by cpufreq_driver_resolve_freq() during the update.
> > */
> > - policy->min = new_data.min;
> > - policy->max = new_data.max;
> > - policy->min = __resolve_freq(policy, policy->min, CPUFREQ_RELATION_L);
> > - policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
> > + WRITE_ONCE(policy->max, __resolve_freq(policy, new_data.max, CPUFREQ_RELATION_H));
> > + new_data.min = __resolve_freq(policy, new_data.min, CPUFREQ_RELATION_L);
> > + WRITE_ONCE(policy->min, new_data.min > policy->max ? policy->max : new_data.min);
>
> I've tested the cpufreq throttling again in 6.15-rc3 to check your fix
> for the schedutil CPUFREQ_NEED_UPDATE_LIMITS regression I reported [1].
> The CPU frequency is now being throttled correctly when reaching high
> temperatures. Thanks for fixing this!
>
> Unfortunately, the opposite case has now regressed with this patch:
> After the CPU frequency has been throttled due to high temperature and
> the device cools down again, the CPU frequency is stuck at minimum until
> you reboot. policy->max will never restore to the maximum frequency.
>
> I've confirmed that this causes unexpected slowness after temperature
> throttling on a Qualcomm X1E laptop, and Johan has confirmed that e.g.
> the ThinkPad X13s is also affected. I would expect that most devices
> using cpufreq cooling in the kernel are affected.
>
> Looking at the code, I think the problem is that __resolve_freq() ->
> cpufreq_frequency_table_target() -> cpufreq_table_find_index*() and
> cpufreq_is_in_limits() are still using the old policy->min/max value.
> In this patch, you have only moved the clamp_val() usage directly in
> __resolve_freq().
You are right, that's the problem.
The fix is basically straightforward, pass min and max to
cpufreq_frequency_table_target() and propagate downward, but making
that change may be somewhat error-prone.
I'll try to cut a patch to test tomorrow.
Thanks!
On 16-04-25, 16:12, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Since cpufreq_driver_resolve_freq() can run in parallel with
> cpufreq_set_policy() and there is no synchronization between them,
> the former may access policy->min and policy->max while the latter
> is updating them and it may see intermediate values of them due
> to the way the update is carried out. Also the compiler is free
> to apply any optimizations it wants both to the stores in
> cpufreq_set_policy() and to the loads in cpufreq_driver_resolve_freq()
> which may result in additional inconsistencies.
>
> To address this, use WRITE_ONCE() when updating policy->min and
> policy->max in cpufreq_set_policy() and use READ_ONCE() for reading
> them in cpufreq_driver_resolve_freq(). Moreover, rearrange the update
> in cpufreq_set_policy() to avoid storing intermediate values in
> policy->min and policy->max with the help of the observation that
> their new values are expected to be properly ordered upfront.
>
> Also modify cpufreq_driver_resolve_freq() to take the possible reverse
> ordering of policy->min and policy->max, which may happen depending on
> the ordering of operations when this function and cpufreq_set_policy()
> run concurrently, into account by always honoring the max when it
> turns out to be less than the min (in case it comes from thermal
> throttling or similar).
>
> Fixes: 151717690694 ("cpufreq: Make policy min/max hard requirements")
> Cc: 5.16+ <stable@vger.kernel.org> # 5.16+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>
> This replaces the last 3 patches in
>
> https://lore.kernel.org/linux-pm/6171293.lOV4Wx5bFT@rjwysocki.net/
>
> v2 -> v3:
> * Fold 3 patches into one.
> * Drop an unrelated white space fixup change.
> * Fix a typo in a comment (Christian).
>
> v1 -> v2: Cosmetic changes
>
> ---
> drivers/cpufreq/cpufreq.c | 32 +++++++++++++++++++++++++-------
> 1 file changed, 25 insertions(+), 7 deletions(-)
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
--
viresh
On 4/16/25 15:12, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Since cpufreq_driver_resolve_freq() can run in parallel with
> cpufreq_set_policy() and there is no synchronization between them,
> the former may access policy->min and policy->max while the latter
> is updating them and it may see intermediate values of them due
> to the way the update is carried out. Also the compiler is free
> to apply any optimizations it wants both to the stores in
> cpufreq_set_policy() and to the loads in cpufreq_driver_resolve_freq()
> which may result in additional inconsistencies.
>
> To address this, use WRITE_ONCE() when updating policy->min and
> policy->max in cpufreq_set_policy() and use READ_ONCE() for reading
> them in cpufreq_driver_resolve_freq(). Moreover, rearrange the update
> in cpufreq_set_policy() to avoid storing intermediate values in
> policy->min and policy->max with the help of the observation that
> their new values are expected to be properly ordered upfront.
>
> Also modify cpufreq_driver_resolve_freq() to take the possible reverse
> ordering of policy->min and policy->max, which may happen depending on
> the ordering of operations when this function and cpufreq_set_policy()
> run concurrently, into account by always honoring the max when it
> turns out to be less than the min (in case it comes from thermal
> throttling or similar).
>
> Fixes: 151717690694 ("cpufreq: Make policy min/max hard requirements")
> Cc: 5.16+ <stable@vger.kernel.org> # 5.16+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
> ---
>
> This replaces the last 3 patches in
>
> https://lore.kernel.org/linux-pm/6171293.lOV4Wx5bFT@rjwysocki.net/
>
> v2 -> v3:
> * Fold 3 patches into one.
> * Drop an unrelated white space fixup change.
> * Fix a typo in a comment (Christian).
>
> v1 -> v2: Cosmetic changes
>
> ---
> drivers/cpufreq/cpufreq.c | 32 +++++++++++++++++++++++++-------
> 1 file changed, 25 insertions(+), 7 deletions(-)
>
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -495,8 +495,6 @@
> {
> unsigned int idx;
>
> - target_freq = clamp_val(target_freq, policy->min, policy->max);
> -
> if (!policy->freq_table)
> return target_freq;
>
> @@ -520,7 +518,22 @@
> unsigned int cpufreq_driver_resolve_freq(struct cpufreq_policy *policy,
> unsigned int target_freq)
> {
> - return __resolve_freq(policy, target_freq, CPUFREQ_RELATION_LE);
> + unsigned int min = READ_ONCE(policy->min);
> + unsigned int max = READ_ONCE(policy->max);
> +
> + /*
> + * If this function runs in parallel with cpufreq_set_policy(), it may
> + * read policy->min before the update and policy->max after the update
> + * or the other way around, so there is no ordering guarantee.
> + *
> + * Resolve this by always honoring the max (in case it comes from
> + * thermal throttling or similar).
> + */
> + if (unlikely(min > max))
> + min = max;
> +
> + return __resolve_freq(policy, clamp_val(target_freq, min, max),
> + CPUFREQ_RELATION_LE);
> }
> EXPORT_SYMBOL_GPL(cpufreq_driver_resolve_freq);
>
> @@ -2338,6 +2351,7 @@
> if (cpufreq_disabled())
> return -ENODEV;
>
> + target_freq = clamp_val(target_freq, policy->min, policy->max);
> target_freq = __resolve_freq(policy, target_freq, relation);
>
> pr_debug("target for CPU %u: %u kHz, relation %u, requested %u kHz\n",
> @@ -2631,11 +2645,15 @@
> * Resolve policy min/max to available frequencies. It ensures
> * no frequency resolution will neither overshoot the requested maximum
> * nor undershoot the requested minimum.
> + *
> + * Avoid storing intermediate values in policy->max or policy->min and
> + * compiler optimizations around them because they may be accessed
> + * concurrently by cpufreq_driver_resolve_freq() during the update.
> */
> - policy->min = new_data.min;
> - policy->max = new_data.max;
> - policy->min = __resolve_freq(policy, policy->min, CPUFREQ_RELATION_L);
> - policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
> + WRITE_ONCE(policy->max, __resolve_freq(policy, new_data.max, CPUFREQ_RELATION_H));
> + new_data.min = __resolve_freq(policy, new_data.min, CPUFREQ_RELATION_L);
> + WRITE_ONCE(policy->min, new_data.min > policy->max ? policy->max : new_data.min);
> +
> trace_cpu_frequency_limits(policy);
>
> cpufreq_update_pressure(policy);
>
>
>
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