Re: [PATCH 1/2] rust: Add initial cpumask abstractions

[Alice Ryhl]

On Tue, Feb 25, 2025 at 11:54 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>
> On 25-02-25, 10:55, Alice Ryhl wrote:
> > On Tue, Feb 25, 2025 at 10:47 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> > > +impl Drop for Cpumask {
> > > +    fn drop(&mut self) {
> > > +        if self.owned {
> > > +            // SAFETY: `ptr` is guaranteed to be valid for the lifetime of `self`. And it is safe
> > > +            // to call `free_cpumask_var()`.
> > > +            unsafe { bindings::free_cpumask_var(self.ptr) }
> >
> > This is missing a semicolon, but it's not the last statement in the
> > block. Did you compile this with CPUMASK_OFFSTACK=n? I don't think it
> > compiles with that setting.
>
> I would always add a semicolon here, yeah I missed adding that but ..
>
> I have missed minor things before sending a series a few times in the
> past and this one really scared me thinking here I did it again :)
>
> Though I was sure that I have built the code with both
> CPUMASK_OFFSTACK=y and =n, I performed the builds again and it worked
> (again).  That confused me even more :)
>
> And here is what I think is happening here (which makes it build fine
> accidentally):
> - free_cpumask_var() has a return type of void.
> - The block {} allows it to build fine without a semicolon here.
> - I performed a simple test for this [1] and it works too.

Ah, you are right, the block makes it work in this particular case.

> > > +            #[cfg(not(CONFIG_CPUMASK_OFFSTACK))]
> > > +            // SAFETY: The pointer was earlier initialized from the result of `KBox::into_raw()`.
> > > +            unsafe {
> > > +                drop(KBox::from_raw(self.ptr))
> > > +            };
> >
> > This looks like you did not run rustfmt.
>
> I did this:
>
> make CLIPPY=1 rustfmtcheck ARCH=arm64 O=../barm64t/ -j8 CROSS_COMPILE=aarch64-linux-gnu- CONFIG_DEBUG_SECTION_MISMATCH=y
>
> I hope that is all I need ? I checked again with both CONFIG options,
> doesn't complain with rustc 1.84.1.

Hmm, ok. I would have expected it to format on one line:
unsafe { drop(KBox::from_raw(self.ptr)) };

That is what normally happens when the semi-colon is outside the
block. Not sure why it did not happen in this case.

Alice