As Wedson Almeida Filho of Google's Android Team said at the time, "We feel that Rust is now ready to join C as a practical language for implementing the kernel. It can help us reduce the number of potential bugs and security vulnerabilities in privileged code while playing nicely with the core kernel and preserving its performance characteristics."
It took a while to convince the top Linux kernel developers of this. There were concerns about non-standard Rust extensions being needed to get it to work in Linux. For instance, with the new Rust Linux NVMe driver, over 70 extensions needed to be made to Rust to get it working. But, Torvalds had told me in an earlier interview, "We've been using exceptions to standard C for decades."
This was still an issue at the invitation-only Linux Kernel Maintainers Summit. But, in the end, it was decided that Rust is well enough supported in the Clang -- the C language family compiler front end -- to move forward. Besides, as Torvalds had said earlier, "Clang does work, so merging Rust would probably help and not hurt the kernel."
At the meeting, Torvalds said, "There was debate at the Maintainers Summit, but it was really mostly about the issue of compiler versions. Which isn't new to Rust (we already have the whole issue on lots of different compiler versions, and gcc vs clang).