linux-kernel - Re: [PATCH v2 2/2] cpufreq: Pass the policy to cpufreq_driver->adjust

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Message-ID: <bqvpt465nowq3jipfsciaoafjpjhu42l63vi6p67qscwx5oil4@t2tkh2u5giuy>
Date: Thu, 15 Jan 2026 09:44:19 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Huang Rui <ray.huang@....com>, 
	"Gautham R. Shenoy" <gautham.shenoy@....com>, Mario Limonciello <mario.limonciello@....com>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, 
	Len Brown <lenb@...nel.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
	Clark Williams <clrkwllms@...nel.org>, Bert Karwatzki <spasswolf@....de>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, Perry Yuan <perry.yuan@....com>
Subject: Re: [PATCH v2 2/2] cpufreq: Pass the policy to
 cpufreq_driver->adjust_perf()

On 14-01-26, 08:51, K Prateek Nayak wrote:
> cpufreq_cpu_get() can sleep on PREEMPT_RT in presence of concurrent
> writer(s), however amd-pstate depends on fetching the cpudata via the
> policy's driver data which necessitates grabbing the reference.
> 
> Since schedutil governor can call "cpufreq_driver->update_perf()"
> during sched_tick/enqueue/dequeue with rq_lock held and IRQs disabled,
> fetching the policy object using the cpufreq_cpu_get() helper in the
> scheduler fast-path leads to "BUG: scheduling while atomic" on
> PREEMPT_RT [1].
> 
> Pass the cached cpufreq policy object in sg_policy to the update_perf()
> instead of just the CPU. The CPU can be inferred using "policy->cpu".
> 
> The lifetime of cpufreq_policy object outlasts that of the governor and
> the cpufreq driver (allocated when the CPU is onlined and only reclaimed
> when the CPU is offlined / the CPU device is removed) which makes it
> safe to be referenced throughout the governor's lifetime.
> 
> Reported-by: Bert Karwatzki <spasswolf@....de>
> Closes:https://lore.kernel.org/all/20250731092316.3191-1-spasswolf@web.de/ [1]
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>

Ahh, you need to fix the Rust binding as well. Minor change there.

-- 
viresh