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

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Message-ID: <87725b0d-42e9-4273-a51f-90c82aad2254@posteo.net>
Date: Mon, 10 Mar 2025 16:09:09 +0000
From: Panagiotis Foliadis <pfoliadis@...teo.net>
To: Alice Ryhl <aliceryhl@...gle.com>
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 10/3/25 12:23, Alice Ryhl wrote:
> 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].

Since the issue focuses on the functions that are trivial wrappers around
c and `do nothing that call a C function` I thought i would leave this out
since there is some other functionality (albeit sometimes minimal) other
that being just a c-wrapper.

>
>> 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>
>>