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Date:   Sun, 25 Jun 2023 21:39:27 +0100
From:   Gary Guo <gary@garyguo.net>
To:     Boqun Feng <boqun.feng@gmail.com>
Cc:     bjorn3_gh@protonmail.com, Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rust: alloc: Add realloc and alloc_zeroed to the
 GlobalAlloc impl
Message-ID: <20230625213927.2e656905.gary@garyguo.net>
In-Reply-To: <ZJXXxEfzVza5Jzxj@boqun-archlinux>
References: <20230622-global_alloc_methods-v1-1-3d3561593e23@protonmail.com>
        <ZJXXxEfzVza5Jzxj@boqun-archlinux>
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On Fri, 23 Jun 2023 10:35:00 -0700
Boqun Feng <boqun.feng@gmail.com> wrote:

> On Thu, Jun 22, 2023 at 09:24:40PM +0200, Bj=C3=B6rn Roy Baron via B4 Rel=
ay wrote:
> > From: Bj=C3=B6rn Roy Baron <bjorn3_gh@protonmail.com>
> >=20
> > While there are default impls for these methods, using the respective C
> > api's is faster. Currently neither the existing nor these new
> > GlobalAlloc method implementations are actually called. Instead the
> > __rust_* function defined below the GlobalAlloc impl are used. With
> > rustc 1.71 these functions will be gone and all allocation calls will g=
o
> > through the GlobalAlloc implementation.
> >=20
> > Link: https://github.com/Rust-for-Linux/linux/issues/68 =20
>=20
> Nice! Although I think we need to do the simialr size adjustment as:
>=20
> 	https://lore.kernel.org/rust-for-linux/20230613164258.3831917-1-boqun.fe=
ng@gmail.com/
>=20
> so I applied your patch onto my patch and came up with the following:

The diff LGTM.

>=20
> --------------------------------->8 =20
> diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
> index ce7a06bf7589..af723c2924dc 100644
> --- a/rust/kernel/allocator.rs
> +++ b/rust/kernel/allocator.rs
> @@ -9,8 +9,17 @@
> =20
>  struct KernelAllocator;
> =20
> -unsafe impl GlobalAlloc for KernelAllocator {
> -    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
> +impl KernelAllocator {
> +    /// # Safety
> +    ///
> +    /// * `ptr` can be either null or a pointer which has been allocated=
 by this allocator.
> +    /// * `layout` must have a non-zero size.
> +    unsafe fn krealloc_with_flags(
> +        &self,
> +        ptr: *mut u8,
> +        layout: Layout,
> +        flags: bindings::gfp_t,
> +    ) -> *mut u8 {
>          // Customized layouts from `Layout::from_size_align()` can have =
size < align, so pads first.
>          let layout =3D layout.pad_to_align();
> =20
> @@ -26,9 +35,22 @@ unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
>              size =3D size.next_power_of_two();
>          }
> =20
> -        // `krealloc()` is used instead of `kmalloc()` because the latte=
r is
> -        // an inline function and cannot be bound to as a result.
> -        unsafe { bindings::krealloc(ptr::null(), size, bindings::GFP_KER=
NEL) as *mut u8 }
> +        // SAFETY:
> +        //
> +        // * `ptr` is either null or a pointer returned from a previous =
k{re}alloc() by the function
> +        //   safety requirement.
> +        //
> +        // * `size` is greater than 0 since it's either a `layout.size()=
` (which cannot be zero
> +        //    according to the function safety requirement) or a result =
from `next_power_of_two()`.
> +        unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, siz=
e, flags) as *mut u8 }
> +    }
> +}
> +
> +unsafe impl GlobalAlloc for KernelAllocator {
> +    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
> +        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero=
 size by the function safety
> +        // requirement.
> +        unsafe { self.krealloc_with_flags(ptr::null_mut(), layout, bindi=
ngs::GFP_KERNEL) }
>      }
> =20
>      unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
> @@ -37,23 +59,30 @@ unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layou=
t) {
>          }
>      }
> =20
> -    unsafe fn realloc(&self, ptr: *mut u8, _layout: Layout, new_size: us=
ize) -> *mut u8 {
> -        unsafe {
> -            bindings::krealloc(
> -                ptr as *const core::ffi::c_void,
> -                new_size,
> -                bindings::GFP_KERNEL,
> -            ) as *mut u8
> -        }
> +    unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usi=
ze) -> *mut u8 {
> +        // SAFETY:
> +        // * `new_size` when rounded up to the nearest multiple of `layo=
ut.align()`, will not
> +        //   overflow `isize` by the function safety requirement.
> +        // * `layout.align()` is a proper alignment (i.e. not zero and m=
ust be a power of two).
> +        let layout =3D unsafe { Layout::from_size_align_unchecked(new_si=
ze, layout.align()) };
> +
> +        // SAFETY:
> +        // * `ptr` is either null or a pointer allocated by this allocat=
or by function safety
> +        //   requirement.
> +        // * the size of `layout` is not zero because `new_size` is not =
zero by function safety
> +        //   requirement.
> +        unsafe { self.krealloc_with_flags(ptr, layout, bindings::GFP_KER=
NEL) }
>      }
> =20
>      unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
> +        // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero=
 size by the function safety
> +        // requirement.
>          unsafe {
> -            bindings::krealloc(
> -                core::ptr::null(),
> -                layout.size(),
> +            self.krealloc_with_flags(
> +                ptr::null_mut(),
> +                layout,
>                  bindings::GFP_KERNEL | bindings::__GFP_ZERO,
> -            ) as *mut u8
> +            )
>          }
>      }
>  }
>=20
>=20
> Regards,
> Boqun
>=20
> > Signed-off-by: Bj=C3=B6rn Roy Baron <bjorn3_gh@protonmail.com>
> > ---
> >  rust/kernel/allocator.rs | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >=20
> > diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
> > index 397a3dd57a9b..e0a27b1326b5 100644
> > --- a/rust/kernel/allocator.rs
> > +++ b/rust/kernel/allocator.rs
> > @@ -21,6 +21,26 @@ unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layo=
ut) {
> >              bindings::kfree(ptr as *const core::ffi::c_void);
> >          }
> >      }
> > +
> > +    unsafe fn realloc(&self, ptr: *mut u8, _layout: Layout, new_size: =
usize) -> *mut u8 {
> > +        unsafe {
> > +            bindings::krealloc(
> > +                ptr as *const core::ffi::c_void,
> > +                new_size,
> > +                bindings::GFP_KERNEL,
> > +            ) as *mut u8
> > +        }
> > +    }
> > +
> > +    unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
> > +        unsafe {
> > +            bindings::krealloc(
> > +                core::ptr::null(),
> > +                layout.size(),
> > +                bindings::GFP_KERNEL | bindings::__GFP_ZERO,
> > +            ) as *mut u8
> > +        }
> > +    }
> >  }
> > =20
> >  #[global_allocator]
> >=20
> > ---
> > base-commit: d2e3115d717197cb2bc020dd1f06b06538474ac3
> > change-id: 20230622-global_alloc_methods-abf5b5e38dba
> >=20
> > Best regards,
> > --=20
> > Bj=C3=B6rn Roy Baron <bjorn3_gh@protonmail.com>
> >  =20