Re: [PATCH v2 01/83] block: rust: fix `Send` bound for `GenDisk`

[Yuan Tan]

On Tue, Jun 9, 2026 at 12:13 PM Andreas Hindborg <a.hindborg@xxxxxxxxxx> wrote:
>
> The `Send` implementation for `GenDisk<T>` was conditioned on `T: Send`.
> This constrains the wrong type. `T` is the `Operations` implementation,
> which is typically a zero-sized marker type that carries no data, so `T:
> Send` says nothing about whether the data a `GenDisk` actually owns can be
> moved to another thread.
>
> A `GenDisk<T>` owns the queue data `T::QueueData` (stored as the
> `gendisk`'s `queuedata` and dropped when the `GenDisk` is dropped) and an
> `Arc<TagSet<T>>`. These are the values transferred when a `GenDisk` is sent
> across a thread boundary, so the `Send` bound must constrain exactly them.
> Bound `T::QueueData: Send` and `Arc<TagSet<T>>: Send` instead.
>
> Fixes: 3253aba3408a ("rust: block: introduce `kernel::block::mq` module")
> Suggested-by: Yuan Tan <ytan089@xxxxxxx>
> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
> ---
>
> Please take patch from Yuan instead of this one, if they send a fixed
> version [1].
>
> [1] https://lore.kernel.org/r/8839ddc5ff54bf454d508cde91d27d00fc3e2dd8.1780633578.git.ytan089@xxxxxxx

My last email mistakenly enabled html. So I am here to resend it. Hope
it doesn't disturb anyone.

Sorry, I've been busy with other things and haven't had the chance to
send the fixed version.

Thank you very much for reviewing the patch and for preparing the v2 version.

Could you please add the following when applying this patch?
Reported-by: Priya Bala Govindasamy <pgovind2@xxxxxxx>
Reported-by: Dylan Zueck <dzueck@xxxxxxx>

I didn't discover this issue myself. I just helped write the patch and
I don't want them to lose their credit for it.

Please let me know if you would prefer that I send a v3 instead.


> ---
>  rust/kernel/block/mq/gen_disk.rs | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
> index 912cb805caf5..b36d24382cc3 100644
> --- a/rust/kernel/block/mq/gen_disk.rs
> +++ b/rust/kernel/block/mq/gen_disk.rs
> @@ -199,8 +199,14 @@ pub struct GenDisk<T: Operations> {
>  }
>
>  // SAFETY: `GenDisk` is an owned pointer to a `struct gendisk` and an `Arc` to a
> -// `TagSet` It is safe to send this to other threads as long as T is Send.
> -unsafe impl<T: Operations + Send> Send for GenDisk<T> {}
> +// `TagSet`. It is safe to send this to other threads as long as these two are `Send`.
> +unsafe impl<T> Send for GenDisk<T>
> +where
> +    T: Operations,
> +    T::QueueData: Send,
> +    Arc<TagSet<T>>: Send,
> +{
> +}
>
>  impl<T: Operations> Drop for GenDisk<T> {
>      fn drop(&mut self) {
>
> --
> 2.51.2
>
>