linux-kernel - Re: [PATCH] rust: task: mark Task methods inline

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Message-ID: <CAH5fLgi1YOP9gbXEmYfBtjWeMaqsYpNrrC1fd2rGABCKWYVcbg@mail.gmail.com>
Date: Mon, 10 Mar 2025 11:23:22 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Panagiotis Foliadis <pfoliadis@...teo.net>
Cc: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Andreas Hindborg <a.hindborg@...nel.org>, 
	Trevor Gross <tmgross@...ch.edu>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] rust: task: mark Task methods inline

On Mon, Mar 10, 2025 at 10:40 AM Panagiotis Foliadis
<pfoliadis@...teo.net> wrote:
>
> When you build the kernel using the llvm-18.1.3-rust-1.85.0-x86_64
> toolchain provided by kernel.org, the following symbols are generated:
>
> $ nm vmlinux | grep ' _R'.*Task | rustfilt
> ffffffff817b2d30 T <kernel::task::Task>::get_pid_ns
> ffffffff817b2d50 T <kernel::task::Task>::tgid_nr_ns
> ffffffff817b2c90 T <kernel::task::Task>::current_pid_ns
> ffffffff817b2d00 T <kernel::task::Task>::signal_pending
> ffffffff817b2cc0 T <kernel::task::Task>::uid
> ffffffff817b2ce0 T <kernel::task::Task>::euid
> ffffffff817b2c70 T <kernel::task::Task>::current
> ffffffff817b2d70 T <kernel::task::Task>::wake_up
> ffffffff817b2db0 T <kernel::task::Task as kernel::types::AlwaysRefCounted>::dec_ref
> ffffffff817b2d90 T <kernel::task::Task as kernel::types::AlwaysRefCounted>::inc_ref
>
> Most of these Rust symbols are trivial wrappers around the C functions
> signal_pending, uid, euid, wake_up, dec_ref and inc_ref.It doesn't
> make sense to go through a trivial wrapper for these functions, so
> mark them inline.

There's no C function called dec_ref or inc_ref? Please use the C
function names instead of the Rust ones.

> After applying this patch, the above command will produce this output:
>
> ffff8000805aa004 T <kernel::task::Task>::get_pid_ns
> ffff8000805aa01c T <kernel::task::Task>::tgid_nr_ns
> ffff8000805a9fe8 T <kernel::task::Task>::current_pid_ns
> ffff8000805a9fd0 T <kernel::task::Task>::current

I think it'd be nice with an explanation of why you did not mark these
#[inline].

> Signed-off-by: Panagiotis Foliadis <pfoliadis@...teo.net>
> Link: https://github.com/Rust-for-Linux/linux/issues/1145

The SoB usually goes at the bottom of the tags.

>  rust/kernel/task.rs | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs
> index 07bc22a7645c0c7d792a0a163dd55b8ff0fe5f92..996d7c96e48689a5752817f9ca196c021865291d 100644
> --- a/rust/kernel/task.rs
> +++ b/rust/kernel/task.rs
> @@ -273,18 +273,21 @@ pub fn pid(&self) -> Pid {
>      }
>
>      /// Returns the UID of the given task.
> +    #[inline]
>      pub fn uid(&self) -> Kuid {
>          // SAFETY: It's always safe to call `task_uid` on a valid task.
>          Kuid::from_raw(unsafe { bindings::task_uid(self.as_ptr()) })
>      }
>
>      /// Returns the effective UID of the given task.
> +    #[inline]
>      pub fn euid(&self) -> Kuid {
>          // SAFETY: It's always safe to call `task_euid` on a valid task.
>          Kuid::from_raw(unsafe { bindings::task_euid(self.as_ptr()) })
>      }
>
>      /// Determines whether the given task has pending signals.
> +    #[inline]
>      pub fn signal_pending(&self) -> bool {
>          // SAFETY: It's always safe to call `signal_pending` on a valid task.
>          unsafe { bindings::signal_pending(self.as_ptr()) != 0 }
> @@ -319,6 +322,7 @@ pub fn tgid_nr_ns(&self, pidns: Option<&PidNamespace>) -> Pid {
>      }
>
>      /// Wakes up the task.
> +    #[inline]
>      pub fn wake_up(&self) {
>          // SAFETY: It's always safe to call `signal_pending` on a valid task, even if the task
>          // running.
> @@ -328,11 +332,13 @@ pub fn wake_up(&self) {
>
>  // SAFETY: The type invariants guarantee that `Task` is always refcounted.
>  unsafe impl crate::types::AlwaysRefCounted for Task {
> +    #[inline]
>      fn inc_ref(&self) {
>          // SAFETY: The existence of a shared reference means that the refcount is nonzero.
>          unsafe { bindings::get_task_struct(self.as_ptr()) };
>      }
>
> +    #[inline]
>      unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
>          // SAFETY: The safety requirements guarantee that the refcount is nonzero.
>          unsafe { bindings::put_task_struct(obj.cast().as_ptr()) }
>
> ---
> base-commit: 7f0e9ee5e44887272627d0fcde0b19a675daf597
> change-id: 20250308-inline-c-wrappers-da83ec1c2a77
>
> Best regards,
> --
> Panagiotis Foliadis <pfoliadis@...teo.net>
>