The vulnerability in the Linux kernel concerns the Spreadtrum EIC GPIO controller's irq startup path, specifically in the sprd_eic_irq_unmask() function. This function enables the GPIO IRQ and updates controller state while holding a spin_lock_irqsave() lock. Under PREEMPT_RT (real-time) kernel configurations, spinlock_t can become a sleeping lock, which is invalid in this context and leads to kernel BUGs. The issue was detected by static analysis and confirmed by a proof-of-concept triggering lockdep warnings about sleeping functions called from invalid contexts. The remediation involved converting the controller lock from spinlock_t to raw_spinlock_t, which does not sleep and is appropriate for irqchip callbacks that only serialize MMIO register updates without sleepable operations.

The vulnerability causes kernel instability and BUGs due to improper locking in the IRQ startup path under PREEMPT_RT configurations. This can lead to kernel crashes or unpredictable behavior when setting up GPIO interrupts on affected hardware using the Spreadtrum EIC controller. There is no indication of direct code execution or privilege escalation from the provided data.

A fix is available that converts the Spreadtrum EIC controller lock to raw_spinlock_t to prevent sleeping in the irq startup path. Users should update to a Linux kernel version that includes this fix. Since no vendor advisory or patch links are provided, check the official Linux kernel repositories or distributions for the patch corresponding to CVE-2026-64429.