scsi: ufs: core: Fix data race in CPU latency PM QoS request handling

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

Introduces a dedicated mutex to serialize PM QoS operations, preventing
data races and ensuring safe access to PM QoS resources, including sysfs
interface reads.

Fixes: 2777e73 ("scsi: ufs: core: Add CPU latency QoS support for UFS driver")
Signed-off-by: Zhongqiu Han <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Tested-by: Huan Tang <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: Zhongqiu Han

drivers/ufs/core/ufs-sysfs.c

@@ -512,6 +512,8 @@ static ssize_t pm_qos_enable_show(struct device *dev,
 {
 	struct ufs_hba *hba = dev_get_drvdata(dev);
 
+	guard(mutex)(&hba->pm_qos_mutex);
+
 	return sysfs_emit(buf, "%d\n", hba->pm_qos_enabled);
 }
 

drivers/ufs/core/ufshcd.c

@@ -1045,6 +1045,7 @@ EXPORT_SYMBOL_GPL(ufshcd_is_hba_active);
  */
 void ufshcd_pm_qos_init(struct ufs_hba *hba)
 {
+	guard(mutex)(&hba->pm_qos_mutex);
 
 	if (hba->pm_qos_enabled)
 		return;
@@ -1061,6 +1062,8 @@ void ufshcd_pm_qos_init(struct ufs_hba *hba)
  */
 void ufshcd_pm_qos_exit(struct ufs_hba *hba)
 {
+	guard(mutex)(&hba->pm_qos_mutex);
+
 	if (!hba->pm_qos_enabled)
 		return;
 
@@ -1075,6 +1078,8 @@ void ufshcd_pm_qos_exit(struct ufs_hba *hba)
  */
 static void ufshcd_pm_qos_update(struct ufs_hba *hba, bool on)
 {
+	guard(mutex)(&hba->pm_qos_mutex);
+
 	if (!hba->pm_qos_enabled)
 		return;
 
@@ -10743,6 +10748,10 @@ 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);

include/ufs/ufshcd.h

@@ -938,6 +938,7 @@ 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
@@ -1110,6 +1111,8 @@ struct ufs_hba {
 	struct delayed_work ufs_rtc_update_work;
 	struct pm_qos_request pm_qos_req;
 	bool pm_qos_enabled;
+	/* synchronizes PM QoS request and status updates */
+	struct mutex pm_qos_mutex;
 
 	int critical_health_count;
 	atomic_t dev_lvl_exception_count;