hwmon: (pmbus/core) Protect regulator operations with mutex

Overview

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

hwmon: (pmbus/core) Protect regulator operations with mutex

The regulator operations pmbus_regulator_get_voltage(), pmbus_regulator_set_voltage(), and pmbus_regulator_list_voltage() access PMBus registers and shared data but were not protected by the update_lock mutex. This could lead to race conditions.

However, adding mutex protection directly to these functions causes a deadlock because pmbus_regulator_notify() (which calls regulator_notifier_call_chain()) is often called with the mutex already held (e.g., from pmbus_fault_handler()). If a regulator callback then calls one of the now-protected voltage functions, it will attempt to acquire the same mutex.

Rework pmbus_regulator_notify() to utilize a worker function to send notifications outside of the mutex protection. Events are stored as atomics in a per-page bitmask and processed by the worker.

Initialize the worker and its associated data during regulator registration, and ensure it is cancelled on device removal using devm_add_action_or_reset().

While at it, remove the unnecessary include of linux/of.h.

Affected

• Linux >= ddbb4db4ced1ba784fcd3500179a7291b6c5d7b7 < b26849cffaa7c43355b82e9bef3725e786973a1a
• Linux >= ddbb4db4ced1ba784fcd3500179a7291b6c5d7b7 < acf04e2863132f6d9222f71f3a76fb9782cbe061
• Linux >= ddbb4db4ced1ba784fcd3500179a7291b6c5d7b7 < 4e9d723d9f198b86f6882a84c501ba1f39e8d055
• Linux >= ddbb4db4ced1ba784fcd3500179a7291b6c5d7b7 < 2c77ae315f3ce9d2c8e1609be74c9358c1fe4e07
• Linux >= ddbb4db4ced1ba784fcd3500179a7291b6c5d7b7 < 754bd2b4a084b90b5e7b630e1f423061a9b9b761
• Linux 3.19

Remediation

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