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

Overview

In the Linux kernel, the following vulnerability has been resolved:

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.

Affected

• Linux >= 2777e73fc154e2e87233bdcc0e2402b33815198e < eee1b13526b8f1e6a2402973d95f9fa854771f57
• Linux >= 2777e73fc154e2e87233bdcc0e2402b33815198e < d9df61afb8d23c475f1be3c714da2c34c156ab01
• Linux >= 2777e73fc154e2e87233bdcc0e2402b33815198e < 79dde5f7dc7c038eec903745dc1550cd4139980e
• Linux 6.9

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.