Feels like an antipattern. If you're doing high-speed stuff where a context switch to kernel mode and back would kill you, then you really want an RTOS with virtually no attack surface, instead of trying to hack it into the Linux kernel. Because with the Linux kernel, you'll be tempted to run less-secure code on there, because you might become overconfident in the kernel's security (which you've just co-opted by adding a custom in-kernel database engine or something).