#define Labyrinth (void *)alloc_page(gfp_atomic) Patched

The student, Kai, rubbed their eyes. “It’s for the memory allocator. The kernel panics when the page fault handler runs out of scratch space. So I’m defining a labyrinth —a raw, atomic page of memory we can escape into when the normal paths are blocked.”

: This is the identifier or name of the macro being defined. #define labyrinth (void *)alloc_page(gfp_atomic)

Here's what happens when you use this macro: The student, Kai, rubbed their eyes

: The "Get Free Page" (GFP) flags dictate how the allocator behaves. Using GFP_ATOMIC tells the kernel that the allocation must succeed or fail immediately. It is strictly used in contexts where the kernel cannot sleep, such as interrupt handlers or when holding a spinlock . So I’m defining a labyrinth —a raw, atomic

Defining labyrinth as (void *)alloc_page(gfp_atomic) essentially creates a shortcut for allocating a page of memory with atomic GFP flags. Anywhere labyrinth appears in the code will be replaced with (void *)alloc_page(gfp_atomic) .

In general, it's essential to carefully evaluate the need for atomic allocations and consider alternative approaches, such as using a non-atomic allocation with a suitable fallback strategy. Additionally, always check the return value of the allocation to handle potential failures.

“Exactly,” Kai said. “Theseus had a thread. We have a page.”