Re: [PATCH v2 3/4] rust: sync: add `CondVar::wait_timeout`

Boqun Feng
2023-12-18T21:15:26Z

On Sat, Dec 16, 2023 at 03:31:41PM +0000, Alice Ryhl wrote:
> Sleep on a condition variable with a timeout.
>
> This is used by Rust Binder for process freezing. There, we want to
> sleep until the freeze operation completes, but we want to be able to
> abort the process freezing if it doesn't complete within some timeout.
>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
> rust/kernel/sync/condvar.rs | 59 ++++++++++++++++++++++++++++++++++++++++-----
> rust/kernel/sync/lock.rs | 4 +--
> 2 files changed, 55 insertions(+), 8 deletions(-)
>
> diff --git a/rust/kernel/sync/condvar.rs b/rust/kernel/sync/condvar.rs
> index 9331eb606738..0176cdfced6c 100644
> --- a/rust/kernel/sync/condvar.rs
> +++ b/rust/kernel/sync/condvar.rs
> @@ -6,7 +6,8 @@
> //! variable.
>
> use super::{lock::Backend, lock::Guard, LockClassKey};
> -use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque};
> +use crate::{bindings, init::PinInit, pin_init, str::CStr, time::Jiffies, types::Opaque};
> +use core::ffi::c_long;
> use core::marker::PhantomPinned;
> use macros::pin_data;
>
> @@ -18,6 +19,8 @@ macro_rules! new_condvar {
> };
> }
>
> +const MAX_SCHEDULE_TIMEOUT: c_long = c_long::MAX;
> +

I'd like to put this in rust/kernel/time.rs or rust/kernel/task.rs, but
it's not a blocker.

> /// A conditional variable.
> ///
> /// Exposes the kernel's [`struct wait_queue_head`] as a condition variable. It allows the caller to
> @@ -102,7 +105,12 @@ pub fn new(name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self
> })
> }
>
> - fn wait_internal<T: ?Sized, B: Backend>(&self, wait_state: u32, guard: &mut Guard<'_, T, B>) {
> + fn wait_internal<T: ?Sized, B: Backend>(
> + &self,
> + wait_state: u32,
> + guard: &mut Guard<'_, T, B>,
> + timeout: c_long,

Nit: maybe `timeout_in_jiffies` instead of `timeout`? Or we have another
data type:

pub type DeltaJiffies = c_long;

or

pub type JiffyDelta = c_long;

because a "c_long timeout" really hurts the readability.

Regards,
Boqun

> + ) -> c_long {
> let wait = Opaque::<bindings::wait_queue_entry>::uninit();
>
> // SAFETY: `wait` points to valid memory.
> @@ -113,11 +121,13 @@ fn wait_internal<T: ?Sized, B: Backend>(&self, wait_state: u32, guard: &mut Guar
> bindings::prepare_to_wait_exclusive(self.wait_list.get(), wait.get(), wait_state as _)
> };
> …