6.6-stable review patch. If anyone has any objections, please let me know.
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From: Rafael J. Wysocki rafael.j.wysocki@intel.com
commit 7491cdf46b5cbdf123fc84fbe0a07e9e3d7b7620 upstream.
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 Acked-by: Viresh Kumar viresh.kumar@linaro.org Link: https://patch.msgid.link/5907080.DvuYhMxLoT@rjwysocki.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/cpufreq/cpufreq.c | 32 +++++++++++++++++++++++++------- 1 file changed, 25 insertions(+), 7 deletions(-)
--- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -538,8 +538,6 @@ static unsigned int __resolve_freq(struc { unsigned int idx;
- target_freq = clamp_val(target_freq, policy->min, policy->max); - if (!policy->freq_table) return target_freq;
@@ -563,7 +561,22 @@ static unsigned int __resolve_freq(struc 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);
@@ -2335,6 +2348,7 @@ int __cpufreq_driver_target(struct cpufr 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", @@ -2625,11 +2639,15 @@ static int cpufreq_set_policy(struct cpu * 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);
policy->cached_target_freq = UINT_MAX;