linux-kernel - Re: [PATCH v1 1/3] cpufreq: intel_pstate: Fix object lifecycle issue in update_qos

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Message-ID: <f099c236-b9d5-4d73-9176-c91f54acffd0@kylinos.cn>
Date: Mon, 8 Sep 2025 08:41:10 +0800
From: Zihuan Zhang <zhangzihuan@...inos.cn>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
 Linux PM <linux-pm@...r.kernel.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 LKML <linux-kernel@...r.kernel.org>, Viresh Kumar <viresh.kumar@...aro.org>,
 Jonathan Cameron <jonathan.cameron@...wei.com>
Subject: Re: [PATCH v1 1/3] cpufreq: intel_pstate: Fix object lifecycle issue
 in update_qos_request()


在 2025/9/5 21:52, Rafael J. Wysocki 写道:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> The cpufreq_cpu_put() call in update_qos_request() takes place too early
> because the latter subsequently calls freq_qos_update_request() that
> indirectly accesses the policy object in question through the QoS request
> object passed to it.
>
> Fortunately, update_qos_request() is called under intel_pstate_driver_lock,
> so this issue does not matter for changing the intel_pstate operation
> mode, but it theoretically can cause a crash to occur on CPU device hot
> removal (which currently can only happen in virt, but it is formally
> supported nevertheless).
>
> Address this issue by modifying update_qos_request() to drop the
> reference to the policy later.
>
> Fixes: da5c504c7aae ("cpufreq: intel_pstate: Implement QoS supported freq constraints")
> Cc: 5.4+ <stable@...r.kernel.org> # 5.4+
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>   drivers/cpufreq/intel_pstate.c |    8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -1708,10 +1708,10 @@ static void update_qos_request(enum freq
>   			continue;
>   
>   		req = policy->driver_data;
> -		cpufreq_cpu_put(policy);
> -
> -		if (!req)
> +		if (!req) {
> +			cpufreq_cpu_put(policy);
>   			continue;
> +		}
>   
>   		if (hwp_active)
>   			intel_pstate_get_hwp_cap(cpu);
> @@ -1727,6 +1727,8 @@ static void update_qos_request(enum freq
>   
>   		if (freq_qos_update_request(req, freq) < 0)
>   			pr_warn("Failed to update freq constraint: CPU%d\n", i);
> +
> +		cpufreq_cpu_put(policy);
>   	}
>   }
>   
Reviewed-by: Zihuan Zhang <zhangzihuan@...inos.cn>