Calling `virtio_free_buf` or `kmm_free` inside IRQ may lead to dead lock
inside `mm_free`, so we use a free list to store the buffer and reuse it
next time. Fortunately, NuttX only uses one async buffer at same time,
so we don't need to consider how to free the buffer because we won't
have too many in the free list.
Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>
Zhe Weng
f4bfde4d47