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charset=utf-8 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.700.81\)) Subject: Re: [PATCH v6 17/18] rust: block: add remote completion to `Request` From: Daniel Almeida In-Reply-To: <20250822-rnull-up-v6-16-v6-17-ec65006e2f07@kernel.org> Date: Wed, 27 Aug 2025 15:00:19 -0300 Cc: Boqun Feng , Miguel Ojeda , Alex Gaynor , Gary Guo , =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Alice Ryhl , Trevor Gross , Danilo Krummrich , Jens Axboe , Breno Leitao , linux-block@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <680BB9D0-3720-44EC-A25D-83806F635D8D@collabora.com> References: <20250822-rnull-up-v6-16-v6-0-ec65006e2f07@kernel.org> <20250822-rnull-up-v6-16-v6-17-ec65006e2f07@kernel.org> To: Andreas Hindborg X-Mailer: Apple Mail (2.3826.700.81) X-ZohoMailClient: External Hi Andreas, > On 22 Aug 2025, at 09:14, Andreas Hindborg = wrote: >=20 > Allow users of rust block device driver API to schedule completion of > requests via `blk_mq_complete_request_remote`. >=20 > Reviewed-by: Alice Ryhl > Reviewed-by: Daniel Almeida > Signed-off-by: Andreas Hindborg > --- > drivers/block/rnull/rnull.rs | 9 +++++++++ > rust/kernel/block/mq.rs | 6 ++++++ > rust/kernel/block/mq/operations.rs | 19 +++++++++++++++---- > rust/kernel/block/mq/request.rs | 17 +++++++++++++++++ > 4 files changed, 47 insertions(+), 4 deletions(-) >=20 > diff --git a/drivers/block/rnull/rnull.rs = b/drivers/block/rnull/rnull.rs > index 8255236bc550..a19c55717c4f 100644 > --- a/drivers/block/rnull/rnull.rs > +++ b/drivers/block/rnull/rnull.rs > @@ -82,4 +82,13 @@ fn queue_rq(_queue_data: (), rq: = ARef>, _is_last: bool) -> Res > } >=20 > fn commit_rqs(_queue_data: ()) {} > + > + fn complete(rq: ARef>) { > + mq::Request::end_ok(rq) > + .map_err(|_e| kernel::error::code::EIO) > + // We take no refcounts on the request, so we expect to = be able to > + // end the request. The request reference must be unique = at this > + // point, and so `end_ok` cannot fail. > + .expect("Fatal error - expected to be able to end = request"); > + } > } > diff --git a/rust/kernel/block/mq.rs b/rust/kernel/block/mq.rs > index 6e546f4f3d1c..c0ec06b84355 100644 > --- a/rust/kernel/block/mq.rs > +++ b/rust/kernel/block/mq.rs > @@ -77,6 +77,12 @@ > //! } > //! > //! fn commit_rqs(_queue_data: ()) {} > +//! > +//! fn complete(rq: ARef>) { > +//! Request::end_ok(rq) > +//! .map_err(|_e| kernel::error::code::EIO) > +//! .expect("Fatal error - expected to be able to end = request"); > +//! } > //! } > //! > //! let tagset: Arc> =3D > diff --git a/rust/kernel/block/mq/operations.rs = b/rust/kernel/block/mq/operations.rs > index 6fb256f55acc..0fece577de7c 100644 > --- a/rust/kernel/block/mq/operations.rs > +++ b/rust/kernel/block/mq/operations.rs > @@ -42,6 +42,9 @@ fn queue_rq( > /// Called by the kernel to indicate that queued requests should = be submitted. > fn commit_rqs(queue_data: ForeignBorrowed<'_, Self::QueueData>); >=20 > + /// Called by the kernel when the request is completed. > + fn complete(rq: ARef>); > + > /// Called by the kernel to poll the device for completed = requests. Only > /// used for poll queues. > fn poll() -> bool { > @@ -143,13 +146,21 @@ impl OperationsVTable { > T::commit_rqs(queue_data) > } >=20 > - /// This function is called by the C kernel. It is not currently > - /// implemented, and there is no way to exercise this code path. > + /// This function is called by the C kernel. A pointer to this = function is > + /// installed in the `blk_mq_ops` vtable for the driver. > /// > /// # Safety > /// > - /// This function may only be called by blk-mq C infrastructure. > - unsafe extern "C" fn complete_callback(_rq: *mut = bindings::request) {} > + /// This function may only be called by blk-mq C infrastructure. = `rq` must > + /// point to a valid request that has been marked as completed. = The pointee > + /// of `rq` must be valid for write for the duration of this = function. > + unsafe extern "C" fn complete_callback(rq: *mut = bindings::request) { > + // SAFETY: This function can only be dispatched through > + // `Request::complete`. We leaked a refcount then which we = pick back up > + // now. > + let aref =3D unsafe { Request::aref_from_raw(rq) }; > + T::complete(aref); > + } >=20 > /// This function is called by the C kernel. A pointer to this = function is > /// installed in the `blk_mq_ops` vtable for the driver. > diff --git a/rust/kernel/block/mq/request.rs = b/rust/kernel/block/mq/request.rs > index 3848cfe63f77..f7f757f7459f 100644 > --- a/rust/kernel/block/mq/request.rs > +++ b/rust/kernel/block/mq/request.rs > @@ -135,6 +135,23 @@ pub fn end_ok(this: ARef) -> Result<(), = ARef> { > Ok(()) > } >=20 > + /// Complete the request by scheduling `Operations::complete` for > + /// execution. > + /// > + /// The function may be scheduled locally, via SoftIRQ or = remotely via IPMI. > + /// See `blk_mq_complete_request_remote` in [`blk-mq.c`] for = details. > + /// > + /// [`blk-mq.c`]: srctree/block/blk-mq.c > + pub fn complete(this: ARef) { > + let ptr =3D = ARef::into_raw(this).cast::().as_ptr(); > + // SAFETY: By type invariant, `self.0` is a valid `struct = request` > + if !unsafe { bindings::blk_mq_complete_request_remote(ptr) } = { > + // SAFETY: We released a refcount above that we can = reclaim here. > + let this =3D unsafe { Request::aref_from_raw(ptr) }; > + T::complete(this); > + } > + } > + > /// Return a pointer to the [`RequestDataWrapper`] stored in the = private area > /// of the request structure. > /// >=20 > --=20 > 2.47.2 >=20 >=20 I had another look here. While I do trust your reasoning, perhaps we = should remove the call to expect()? If it is not called ever as you said, great, removing the expect() will = not change the code behavior. If it is, be it because of some minor = oversight or unexpected condition, we should produce some error output instead of = crashing the kernel. Maybe we should use a warn() here instead? Or maybe = dev/pr_err as applicable? =E2=80=94 Daniel=