net: enetc: fix the deadlock of enetc_mdio_lock

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: enetc: fix the deadlock of enetc_mdio_lock After applying the workaround for err050089, the LS1028A platform experiences RCU stalls on RT kernel. This issue is caused by the recursive acquisition of the read lock enetc_mdio_lock. Here list some of the call stacks identified under the enetc_poll path that may lead to a deadlock: enetc_poll -> enetc_lock_mdio -> enetc_clean_rx_ring OR napi_complete_done -> napi_gro_receive -> enetc_start_xmit -> enetc_lock_mdio -> enetc_map_tx_buffs -> enetc_unlock_mdio -> enetc_unlock_mdio After enetc_poll acquires the read lock, a higher-priority writer attempts to acquire the lock, causing preemption. The writer detects that a read lock is already held and is scheduled out. However, readers under enetc_poll cannot acquire the read lock again because a writer is already waiting, leading to a thread hang. Currently, the deadlock is avoided by adjusting enetc_lock_mdio to prevent recursive lock acquisition.

References

• https://git.kernel.org/stable/c/a649161526736f48bcc592e3a412e5bcd7dd9e24
• https://git.kernel.org/stable/c/2781ca82ce8cad263d80b617addb727e6a84c9e5
• https://git.kernel.org/stable/c/1f92f5bd057a4fad9dab6af17963cdd21e5da6ed
• https://git.kernel.org/stable/c/2e55a49dc3b2a6b23329e4fbbd8a5feb20e220aa
• https://git.kernel.org/stable/c/50bd33f6b3922a6b760aa30d409cae891cec8fb5