Re: [PATCH v5 02/15] rust: sync: completion: add wait_for_completion_timeout()

["Gary Guo" <gary@garyguo.net>]

On Wed Sep 30, 2026 at 4:41 AM BST, John Hubbard wrote:
> From: Joel Fernandes <joelagnelf@nvidia.com>
>
> A driver that runs an interrupt self-test during probe waits for the
> handler to fire. wait_for_completion() has no timeout, so a broken
> interrupt path stalls probe indefinitely. Add a timeout variant of
> wait_for_completion().
>
> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
> Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
> [jhubbard: return the remaining jiffies]
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

This email should have RfL list CC'ed.

> ---
>  rust/kernel/sync/completion.rs | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/sync/completion.rs b/rust/kernel/sync/completion.rs
> index 35ff049ff078..7e8b3c1c880e 100644
> --- a/rust/kernel/sync/completion.rs
> +++ b/rust/kernel/sync/completion.rs
> @@ -6,7 +6,12 @@
>  //!
>  //! C header: [`include/linux/completion.h`](srctree/include/linux/completion.h)
>  
> -use crate::{bindings, prelude::*, types::Opaque};
> +use crate::{
> +    bindings,
> +    prelude::*,
> +    time::Jiffies,
> +    types::Opaque, //
> +};
>  
>  /// Synchronization primitive to signal when a certain task has been completed.
>  ///
> @@ -111,4 +116,20 @@ pub fn wait_for_completion(&self) {
>          // SAFETY: `self.as_raw()` is a pointer to a valid `struct completion`.
>          unsafe { bindings::wait_for_completion(self.as_raw()) };
>      }
> +
> +    /// Wait for completion of a task, with a timeout.
> +    ///
> +    /// This method waits for the completion of a task, or until `timeout` elapses. It is not
> +    /// interruptible. Returns the number of jiffies left when the task completed, or [`None`] if
> +    /// `timeout` elapsed first.
> +    ///
> +    /// See also [`Completion::complete_all`].
> +    #[inline]
> +    pub fn wait_for_completion_timeout(&self, timeout: Jiffies) -> Option<Jiffies> {

NACK. Please use the typed `Delta<Jiffy>`, not this old type alias for c_ulong.
I asked Miguel to take that late last cycle because I know there'll be new users
that want to use Jiffies this cycle!

This would avoid you having to do clamping on the max side (but you still need
to clamp the value to be at least 0). There'll be a helper method for this, but
it isn't available yet.
https://lore.kernel.org/rust-for-linux/20261002050428.2746277-3-tomo@flapping.org/

Best,
Gary

> +        // SAFETY: `self.as_raw()` is a pointer to a valid `struct completion`.
> +        match unsafe { bindings::wait_for_completion_timeout(self.as_raw(), timeout) } {
> +            0 => None,
> +            remaining => Some(remaining),
> +        }
> +    }
>  }