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Message-ID: <1174ecf9-b806-4c2d-b755-8a3cd594d337@oss.qualcomm.com>
Date: Tue, 2 Sep 2025 14:43:19 +0800
From: Ziqi Chen <ziqi.chen@....qualcomm.com>
To: Zhongqiu Han <zhongqiu.han@....qualcomm.com>, alim.akhtar@...sung.com,
avri.altman@....com, bvanassche@....org,
James.Bottomley@...senPartnership.com, martin.petersen@...cle.com
Cc: peter.wang@...iatek.com, tanghuan@...o.com, liu.song13@....com.cn,
quic_nguyenb@...cinc.com, viro@...iv.linux.org.uk, huobean@...il.com,
adrian.hunter@...el.com, can.guo@....qualcomm.com, ebiggers@...nel.org,
neil.armstrong@...aro.org, angelogioacchino.delregno@...labora.com,
quic_narepall@...cinc.com, quic_mnaresh@...cinc.com,
linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
nitin.rawat@....qualcomm.com
Subject: Re: [PATCH] scsi: ufs: core: Fix data race in CPU latency PM QoS
request handling
On 9/1/2025 4:51 PM, Zhongqiu Han wrote:
> The cpu_latency_qos_add/remove/update_request interfaces lack internal
> synchronization by design, requiring the caller to ensure thread safety.
> The current implementation relies on the `pm_qos_enabled` flag, which is
> insufficient to prevent concurrent access and cannot serve as a proper
> synchronization mechanism. This has led to data races and list corruption
> issues.
>
> A typical race condition call trace is:
>
> [Thread A]
> ufshcd_pm_qos_exit()
> --> cpu_latency_qos_remove_request()
> --> cpu_latency_qos_apply();
> --> pm_qos_update_target()
> --> plist_del <--(1) delete plist node
> --> memset(req, 0, sizeof(*req));
> --> hba->pm_qos_enabled = false;
>
> [Thread B]
> ufshcd_devfreq_target
> --> ufshcd_devfreq_scale
> --> ufshcd_scale_clks
> --> ufshcd_pm_qos_update <--(2) pm_qos_enabled is true
> --> cpu_latency_qos_update_request
> --> pm_qos_update_target
> --> plist_del <--(3) plist node use-after-free
>
> This patch introduces a dedicated mutex to serialize PM QoS operations,
> preventing data races and ensuring safe access to PM QoS resources.
> Additionally, READ_ONCE is used in the sysfs interface to ensure atomic
> read access to pm_qos_enabled flag.
>
> Fixes: 2777e73fc154 ("scsi: ufs: core: Add CPU latency QoS support for UFS driver")
> Signed-off-by: Zhongqiu Han <zhongqiu.han@....qualcomm.com>
> ---
> drivers/ufs/core/ufs-sysfs.c | 2 +-
> drivers/ufs/core/ufshcd.c | 16 ++++++++++++++++
> include/ufs/ufshcd.h | 2 ++
> 3 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/ufs/core/ufs-sysfs.c b/drivers/ufs/core/ufs-sysfs.c
> index 4bd7d491e3c5..8f7975010513 100644
> --- a/drivers/ufs/core/ufs-sysfs.c
> +++ b/drivers/ufs/core/ufs-sysfs.c
> @@ -512,7 +512,7 @@ static ssize_t pm_qos_enable_show(struct device *dev,
> {
> struct ufs_hba *hba = dev_get_drvdata(dev);
>
> - return sysfs_emit(buf, "%d\n", hba->pm_qos_enabled);
> + return sysfs_emit(buf, "%d\n", READ_ONCE(hba->pm_qos_enabled));
> }
>
> /**
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 926650412eaa..f259fb1790fa 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -1047,14 +1047,18 @@ EXPORT_SYMBOL_GPL(ufshcd_is_hba_active);
> */
> void ufshcd_pm_qos_init(struct ufs_hba *hba)
> {
> + mutex_lock(&hba->pm_qos_mutex);
>
> if (hba->pm_qos_enabled)
> + mutex_unlock(&hba->pm_qos_mutex);
> return;
Missing the curly braces for this If statement.
>
> cpu_latency_qos_add_request(&hba->pm_qos_req, PM_QOS_DEFAULT_VALUE);
>
> if (cpu_latency_qos_request_active(&hba->pm_qos_req))
> hba->pm_qos_enabled = true;
> +
> + mutex_unlock(&hba->pm_qos_mutex);
> }
>
> /**
> @@ -1063,11 +1067,15 @@ void ufshcd_pm_qos_init(struct ufs_hba *hba)
> */
> void ufshcd_pm_qos_exit(struct ufs_hba *hba)
> {
> + mutex_lock(&hba->pm_qos_mutex);
> +
> if (!hba->pm_qos_enabled)
> + mutex_unlock(&hba->pm_qos_mutex);
> return;
Same here.
> cpu_latency_qos_remove_request(&hba->pm_qos_req);
> hba->pm_qos_enabled = false;
> + mutex_unlock(&hba->pm_qos_mutex);
> }
>
> /**
> @@ -1077,10 +1085,14 @@ void ufshcd_pm_qos_exit(struct ufs_hba *hba)
> */
> static void ufshcd_pm_qos_update(struct ufs_hba *hba, bool on)
> {
> + mutex_lock(&hba->pm_qos_mutex);
> +
> if (!hba->pm_qos_enabled)
> + mutex_unlock(&hba->pm_qos_mutex);
> return;
Same here.
> cpu_latency_qos_update_request(&hba->pm_qos_req, on ? 0 : PM_QOS_DEFAULT_VALUE);
> + mutex_unlock(&hba->pm_qos_mutex);
> }
>
> /**
> @@ -10764,6 +10776,10 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)
> mutex_init(&hba->ee_ctrl_mutex);
>
> mutex_init(&hba->wb_mutex);
> +
> + /* Initialize mutex for PM QoS request synchronization */
> + mutex_init(&hba->pm_qos_mutex);
> +
> init_rwsem(&hba->clk_scaling_lock);
>
> ufshcd_init_clk_gating(hba);
> diff --git a/include/ufs/ufshcd.h b/include/ufs/ufshcd.h
> index 30ff169878dc..e81f4346f168 100644
> --- a/include/ufs/ufshcd.h
> +++ b/include/ufs/ufshcd.h
> @@ -962,6 +962,7 @@ enum ufshcd_mcq_opr {
> * @ufs_rtc_update_work: A work for UFS RTC periodic update
> * @pm_qos_req: PM QoS request handle
> * @pm_qos_enabled: flag to check if pm qos is enabled
> + * @pm_qos_mutex: synchronizes PM QoS request and status updates
> * @critical_health_count: count of critical health exceptions
> * @dev_lvl_exception_count: count of device level exceptions since last reset
> * @dev_lvl_exception_id: vendor specific information about the
> @@ -1135,6 +1136,7 @@ struct ufs_hba {
> struct delayed_work ufs_rtc_update_work;
> struct pm_qos_request pm_qos_req;
> bool pm_qos_enabled;
> + struct mutex pm_qos_mutex;
>
> int critical_health_count;
> atomic_t dev_lvl_exception_count;
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