Re: [RFC 2/2] rust: sync: Add atomic support

[Mark Rutland]

On Wed, Jun 12, 2024 at 03:30:25PM -0700, Boqun Feng wrote:
> Provide two atomic types: AtomicI32 and AtomicI64 with the existing
> implemenation of C atomics. These atomics have the same semantics of the
> corresponding LKMM C atomics, and using one memory (ordering) model
> certainly reduces the reasoning difficulty and potential bugs from the
> interaction of two different memory models.
> 
> Also bump my role to the maintainer of ATOMIC INFRASTRUCTURE to reflect
> my responsiblity on these Rust APIs.
> 
> Note that `Atomic*::new()`s are implemented vi open coding on struct
> atomic*_t. This allows `new()` being a `const` function, so that it can
> be used in constant contexts.
> 
> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>

I have a few minor comments below.

> ---
>  MAINTAINERS                       |    4 +-
>  arch/arm64/kernel/cpufeature.c    |    2 +
>  rust/kernel/sync.rs               |    1 +
>  rust/kernel/sync/atomic.rs        |   63 ++
>  rust/kernel/sync/atomic/impl.rs   | 1375 +++++++++++++++++++++++++++++
>  scripts/atomic/gen-atomics.sh     |    1 +
>  scripts/atomic/gen-rust-atomic.sh |  136 +++
>  7 files changed, 1581 insertions(+), 1 deletion(-)
>  create mode 100644 rust/kernel/sync/atomic.rs
>  create mode 100644 rust/kernel/sync/atomic/impl.rs
>  create mode 100755 scripts/atomic/gen-rust-atomic.sh
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index d6c90161c7bf..a8528d27b260 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3458,7 +3458,7 @@ F:	drivers/input/touchscreen/atmel_mxt_ts.c
>  ATOMIC INFRASTRUCTURE
>  M:	Will Deacon <will@xxxxxxxxxx>
>  M:	Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> -R:	Boqun Feng <boqun.feng@xxxxxxxxx>
> +M:	Boqun Feng <boqun.feng@xxxxxxxxx>
>  R:	Mark Rutland <mark.rutland@xxxxxxx>
>  L:	linux-kernel@xxxxxxxxxxxxxxx
>  S:	Maintained
> @@ -3467,6 +3467,8 @@ F:	arch/*/include/asm/atomic*.h
>  F:	include/*/atomic*.h
>  F:	include/linux/refcount.h
>  F:	scripts/atomic/
> +F:	rust/kernel/sync/atomic.rs
> +F:	rust/kernel/sync/atomic/
>  
>  ATTO EXPRESSSAS SAS/SATA RAID SCSI DRIVER
>  M:	Bradley Grove <linuxdrivers@xxxxxxxxxxxx>
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 48e7029f1054..99e6e2b2867f 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1601,6 +1601,8 @@ static bool
>  has_cpuid_feature(const struct arm64_cpu_capabilities *entry, int scope)
>  {
>  	u64 val = read_scoped_sysreg(entry, scope);
> +	if (entry->capability == ARM64_HAS_LSE_ATOMICS)
> +		return false;
>  	return feature_matches(val, entry);
>  }

As per other replies, this'll obviously need to go.

> diff --git a/rust/kernel/sync/atomic.rs b/rust/kernel/sync/atomic.rs
> new file mode 100644
> index 000000000000..b0f852cf1741
> --- /dev/null
> +++ b/rust/kernel/sync/atomic.rs
> @@ -0,0 +1,63 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Atomic primitives.
> +//!
> +//! These primitives have the same semantics as their C counterparts, for precise definitions of
> +//! the semantics, please refer to tools/memory-model. Note that Linux Kernel Memory (Consistency)
> +//! Model is the only model for Rust development in kernel right now, please avoid to use Rust's
> +//! own atomics.
> +
> +use crate::bindings::{atomic64_t, atomic_t};

As with the last patch, why no atomic_long_t?

[...]

> +#gen_proto_order_variant(meta, pfx, name, sfx, order, atomic, ty, int, raw, arg...)
> +gen_proto_order_variant()
> +{
> +	local meta="$1"; shift
> +	local pfx="$1"; shift
> +	local name="$1"; shift
> +	local sfx="$1"; shift
> +	local order="$1"; shift
> +	local atomic="$1"; shift
> +	local ty="$1"; shift
> +	local int="$1"; shift
> +	local raw="$1"; shift
> +
> +	local fn_name="${raw}${pfx}${name}${sfx}${order}"
> +	local atomicname="${raw}${atomic}_${pfx}${name}${sfx}${order}"
> +
> +	local ret="$(gen_ret_type "${meta}" "${int}")"
> +	local params="$(gen_params "${int}" $@)"
> +	local args="$(gen_args "$@")"
> +	local retstmt="$(gen_ret_stmt "${meta}")"
> +
> +cat <<EOF
> +    /// See \`${atomicname}\`.
> +    #[inline(always)]
> +    pub fn ${fn_name}(&self${params}) ${ret}{
> +        // SAFETY:\`self.0.get()\` is a valid pointer.
> +        unsafe {
> +            ${retstmt}${atomicname}(${args});
> +        }
> +    }
> +EOF
> +}

AFAICT the 'ty' argument (AtomicI32/AtomicI64) isn't used and can be
removed.

Likewise for 'raw'.

> +
> +cat << EOF
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Generated by $0
> +//! DO NOT MODIFY THIS FILE DIRECTLY
> +
> +use super::*;
> +use crate::bindings::*;
> +
> +impl AtomicI32 {
> +EOF
> +
> +grep '^[a-z]' "$1" | while read name meta args; do
> +	gen_proto "${meta}" "${name}" "atomic" "AtomicI32" "i32" "" ${args}

With 'ty' and 'raw' gone, this'd be:

	gen_proto "${meta}" "${name}" "atomic" "i32" ${args}

> +done
> +
> +cat << EOF
> +}
> +
> +impl AtomicI64 {
> +EOF
> +
> +grep '^[a-z]' "$1" | while read name meta args; do
> +	gen_proto "${meta}" "${name}" "atomic64" "AtomicI64" "i64" "" ${args}

With 'ty' and 'raw' gone, this'd be:

	gen_proto "${meta}" "${name}" "atomic64" "i64" ${args}

Mark.

> +done
> +
> +cat << EOF
> +}
> +
> +EOF
> -- 
> 2.45.2
>