On Wed, 25 Oct 2023 at 21:54, Boqun Feng <boqun.feng@xxxxxxxxx> wrote: > > In theory, `read_volatile` and `write_volatile` in Rust can have UB in > case of the data races [1]. However, kernel uses volatiles to implement > READ_ONCE() and WRITE_ONCE(), and expects races on these marked accesses > don't cause UB. And they are proven to have a lot of usages in kernel. > > To close this gap, `read_once` and `write_once` are introduced, they > have the same semantics as `READ_ONCE` and `WRITE_ONCE` especially > regarding data races under the assumption that `read_volatile` and > `write_volatile` have the same behavior as a volatile pointer in C from > a compiler point of view. > > Longer term solution is to work with Rust language side for a better way > to implement `read_once` and `write_once`. But so far, it should be good > enough. One thing you may also want to address is the ability to switch between READ_ONCE implementations depending on config. For one, arm64 with LTO will promote READ_ONCE() to acquires.
