A vulnerability in the Linux kernel's memory management subsystem causes a kernel panic during boot when using a boot-time function tracer with a specific filter. The issue arises because deferred kernel page table freeing is scheduled before the workqueue system is initialized, leading to a null pointer dereference and system crash. The flaw was introduced by a commit that allowed collapsing page tables to free kernel page tables prematurely during early boot. The fix prevents scheduling deferred freeing work while the system is still booting, deferring it until the workqueue is available.