Linux Kernel PREEMPT_RT Deadlock Vulnerability in Deferred IRQ Work Function

A potential deadlock vulnerability has been identified in the Linux kernel's scheduling extension, specifically within PREEMPT_RT enabled kernels. The issue arises in the deferred_irq_workfn() function, which is processed in a per-CPU irq_work task context without disabling interrupts. If the run queue (rq) associated with the current CPU is accessed, a deadlock can occur. This happens because the function can be interrupted while holding a lock, leading to a scenario where two interrupts try to acquire the same lock simultaneously, causing a deadlock. The vulnerability affects several versions of the Linux kernel.

Impact

Exploitation of this vulnerability can lead to a deadlock situation, where the system becomes unresponsive due to two interrupts trying to acquire the same lock at the same time, causing a standstill in processing.

Remediation

The vulnerability has been addressed by modifying the initialization of the deferred IRQ work to ensure it is always executed in a hard interrupt context, preventing the possibility of a deadlock. Users should upgrade to the latest version of the Linux kernel where this fix has been applied.