Re: [RFC v2 02/13] rust: sync: Add basic atomic operation mapping framework
On Fri, Dec 13, 2024 at 03:37:13PM +0100, Alice Ryhl wrote:
[...]
> > > > @@ -0,0 +1,19 @@
> > > > +// SPDX-License-Identifier: GPL-2.0
> > > > +
> > > > +//! Atomic primitives.
> > > > +//!
> > > > +//! These primitives have the same semantics as their C counterparts:
> > > > and the precise definitions of
> > > > +//! semantics can be found at [`LKMM`]. Note that Linux Kernel Memory
> > > > (Consistency) Model is the
> > > > +//! only model for Rust code in kernel, and Rust's own atomics should
> > > > be avoided.
> > > > +//!
> > > > +//! # Data races
> > > > +//!
> > > > +//! [`LKMM`] atomics have different rules regarding data races:
> > > > +//!
> > > > +//! - A normal read doesn't data-race with an atomic read.
> > >
> > > This was fixed:
> > > https://github.com/rust-lang/rust/pull/128778
> > >
> >
> > Yeah, I was aware of that effort, and good to know it's finally merged.
> > Thanks!
> >
> > This will be in 1.83, right? If so, we will still need the above until
> > we bump up the minimal rustc version to 1.83 or beyond. I will handle
> > this properly with the minimal rustc 1.83 (i.e. if this goes in first,
> > will send a follow up patch). I will also mention in the above that this
> > has been changed in 1.83.
> >
> > This also reminds that I should add that LKMM allows mixed-size atomic
> > accesses (as non data race), I will add that in the version.
>
> This is just documentation. I don't think you need to do any special
The PR also contained miri changes, so the same code will be reported
differently by miri. That was what I was thinking of. However, now think
about it, we are not going to use Rust atomics, so this difference
shouldn't affect us. Therefore I agree, I will drop this.
> MSRV handling.
>
> > > > +mod private {
> > > > +/// Sealed trait marker to disable customized impls on atomic
> > > > implementation traits.
> > > > +pub trait Sealed {}
> > > > +}
> > >
> > > Just make the trait unsafe?
> > >
> >
> > And make the safety requirement of `AtomicImpl` something like:
> >
> > The type must have the implementation for atomic operations.
> >
> > ? Hmm.. I don't think that's a good safety requirement TBH. Actually the
> > reason that we need to restrict `AtomicImpl` types is more of an
> > iplementation issue (the implementation need to be done if we want to
> > support i8 or i16) rather than safety issue. So a sealed trait is proper
> > here. Does this make sense? Or am I missing something?
>
> Where is the AtomicImpl trait used?
>
It's used when `impl`ing an `AllowAtomic` type, `AllowAtomic` has an
associate type named `Repr` which must be an `AtomicImpl`, i.e. each
type that has atomic operation support must select the underlying
implementation types (currently we only have i32 and i64 from C side
APIs). Using a sealed trait is appropriate in this case, because unless
you are adding atomic support for different sizes of data, you shouldn't
impl `AtomicImpl`.
Regards,
Boqun
> Alice
Re: [RFC v2 02/13] rust: sync: Add basic atomic operation mapping framework
On Thu, Dec 12, 2024 at 6:07 PM Boqun Feng wrote: > > On Thu, Dec 12, 2024 at 11:51:23AM +0100, Alice Ryhl wrote: > > On Fri, Nov 1, 2024 at 7:03 AM Boqun Feng wrote: > > > > > > Preparation for generic atomic implementation. To unify the > > > ipmlementation of a generic method over `i32` and `i64`, the C side > > > atomic methods need to be grouped so that in a generic method, they can > > > be referred as ::, otherwise their parameters and return > > > value are different between `i32` and `i64`, which would require using > > > `transmute()` to unify the type into a `T`. > > > > > > Introduce `AtomicIpml` to represent a basic type in Rust that has the > > > direct mapping to an atomic implementation from C. This trait is sealed, > > > and currently only `i32` and `i64` ipml this. > > > > There seems to be quite a few instances of "impl" spelled as "ipml" here. > > > > Will fix! > > > > Further, different methods are put into different `*Ops` trait groups, > > > and this is for the future when smaller types like `i8`/`i16` are > > > supported but only with a limited set of API (e.g. only set(), load(), > > > xchg() and cmpxchg(), no add() or sub() etc). > > > > > > While the atomic mod is introduced, documentation is also added for > > > memory models and data races. > > > > > > Also bump my role to the maintainer of ATOMIC INFRASTRUCTURE to reflect > > > my responsiblity on the Rust atomic mod. > > > > > > Signed-off-by: Boqun Feng > > > --- > > > MAINTAINERS| 4 +- > > > rust/kernel/sync.rs| 1 + > > > rust/kernel/sync/atomic.rs | 19 > > > rust/kernel/sync/atomic/ops.rs | 199 + > > > 4 files changed, 222 insertions(+), 1 deletion(-) > > > create mode 100644 rust/kernel/sync/atomic.rs > > > create mode 100644 rust/kernel/sync/atomic/ops.rs > > > > > > diff --git a/MAINTAINERS b/MAINTAINERS > > > index b77f4495dcf4..e09471027a63 100644 > > > --- a/MAINTAINERS > > > +++ b/MAINTAINERS > > > @@ -3635,7 +3635,7 @@ F:drivers/input/touchscreen/atmel_mxt_ts.c > > > ATOMIC INFRASTRUCTURE > > > M: Will Deacon > > > M: Peter Zijlstra > > > -R: Boqun Feng > > > +M: Boqun Feng > > > R: Mark Rutland > > > L: [email protected] > > > S: Maintained > > > @@ -3644,6 +3644,8 @@ 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/ > > > > This is why mod.rs files are superior :) > > > > ;-) Not going to do anything right now, but let me think about this. > > > > @@ -0,0 +1,19 @@ > > > +// SPDX-License-Identifier: GPL-2.0 > > > + > > > +//! Atomic primitives. > > > +//! > > > +//! These primitives have the same semantics as their C counterparts: > > > and the precise definitions of > > > +//! semantics can be found at [`LKMM`]. Note that Linux Kernel Memory > > > (Consistency) Model is the > > > +//! only model for Rust code in kernel, and Rust's own atomics should be > > > avoided. > > > +//! > > > +//! # Data races > > > +//! > > > +//! [`LKMM`] atomics have different rules regarding data races: > > > +//! > > > +//! - A normal read doesn't data-race with an atomic read. > > > > This was fixed: > > https://github.com/rust-lang/rust/pull/128778 > > > > Yeah, I was aware of that effort, and good to know it's finally merged. > Thanks! > > This will be in 1.83, right? If so, we will still need the above until > we bump up the minimal rustc version to 1.83 or beyond. I will handle > this properly with the minimal rustc 1.83 (i.e. if this goes in first, > will send a follow up patch). I will also mention in the above that this > has been changed in 1.83. > > This also reminds that I should add that LKMM allows mixed-size atomic > accesses (as non data race), I will add that in the version. This is just documentation. I don't think you need to do any special MSRV handling. > > > +mod private { > > > +/// Sealed trait marker to disable customized impls on atomic > > > implementation traits. > > > +pub trait Sealed {} > > > +} > > > > Just make the trait unsafe? > > > > And make the safety requirement of `AtomicImpl` something like: > > The type must have the implementation for atomic operations. > > ? Hmm.. I don't think that's a good safety requirement TBH. Actually the > reason that we need to restrict `AtomicImpl` types is more of an > iplementation issue (the implementation need to be done if we want to > support i8 or i16) rather than safety issue. So a sealed trait is proper > here. Does this make sense? Or am I missing something? Where is the AtomicImpl trait used? Alice
Re: [RFC v2 02/13] rust: sync: Add basic atomic operation mapping framework
On Thu, Dec 12, 2024 at 11:51:23AM +0100, Alice Ryhl wrote: > On Fri, Nov 1, 2024 at 7:03 AM Boqun Feng wrote: > > > > Preparation for generic atomic implementation. To unify the > > ipmlementation of a generic method over `i32` and `i64`, the C side > > atomic methods need to be grouped so that in a generic method, they can > > be referred as ::, otherwise their parameters and return > > value are different between `i32` and `i64`, which would require using > > `transmute()` to unify the type into a `T`. > > > > Introduce `AtomicIpml` to represent a basic type in Rust that has the > > direct mapping to an atomic implementation from C. This trait is sealed, > > and currently only `i32` and `i64` ipml this. > > There seems to be quite a few instances of "impl" spelled as "ipml" here. > Will fix! > > Further, different methods are put into different `*Ops` trait groups, > > and this is for the future when smaller types like `i8`/`i16` are > > supported but only with a limited set of API (e.g. only set(), load(), > > xchg() and cmpxchg(), no add() or sub() etc). > > > > While the atomic mod is introduced, documentation is also added for > > memory models and data races. > > > > Also bump my role to the maintainer of ATOMIC INFRASTRUCTURE to reflect > > my responsiblity on the Rust atomic mod. > > > > Signed-off-by: Boqun Feng > > --- > > MAINTAINERS| 4 +- > > rust/kernel/sync.rs| 1 + > > rust/kernel/sync/atomic.rs | 19 > > rust/kernel/sync/atomic/ops.rs | 199 + > > 4 files changed, 222 insertions(+), 1 deletion(-) > > create mode 100644 rust/kernel/sync/atomic.rs > > create mode 100644 rust/kernel/sync/atomic/ops.rs > > > > diff --git a/MAINTAINERS b/MAINTAINERS > > index b77f4495dcf4..e09471027a63 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -3635,7 +3635,7 @@ F:drivers/input/touchscreen/atmel_mxt_ts.c > > ATOMIC INFRASTRUCTURE > > M: Will Deacon > > M: Peter Zijlstra > > -R: Boqun Feng > > +M: Boqun Feng > > R: Mark Rutland > > L: [email protected] > > S: Maintained > > @@ -3644,6 +3644,8 @@ 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/ > > This is why mod.rs files are superior :) > ;-) Not going to do anything right now, but let me think about this. > > @@ -0,0 +1,19 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > + > > +//! Atomic primitives. > > +//! > > +//! These primitives have the same semantics as their C counterparts: and > > the precise definitions of > > +//! semantics can be found at [`LKMM`]. Note that Linux Kernel Memory > > (Consistency) Model is the > > +//! only model for Rust code in kernel, and Rust's own atomics should be > > avoided. > > +//! > > +//! # Data races > > +//! > > +//! [`LKMM`] atomics have different rules regarding data races: > > +//! > > +//! - A normal read doesn't data-race with an atomic read. > > This was fixed: > https://github.com/rust-lang/rust/pull/128778 > Yeah, I was aware of that effort, and good to know it's finally merged. Thanks! This will be in 1.83, right? If so, we will still need the above until we bump up the minimal rustc version to 1.83 or beyond. I will handle this properly with the minimal rustc 1.83 (i.e. if this goes in first, will send a follow up patch). I will also mention in the above that this has been changed in 1.83. This also reminds that I should add that LKMM allows mixed-size atomic accesses (as non data race), I will add that in the version. > > +mod private { > > +/// Sealed trait marker to disable customized impls on atomic > > implementation traits. > > +pub trait Sealed {} > > +} > > Just make the trait unsafe? > And make the safety requirement of `AtomicImpl` something like: The type must have the implementation for atomic operations. ? Hmm.. I don't think that's a good safety requirement TBH. Actually the reason that we need to restrict `AtomicImpl` types is more of an iplementation issue (the implementation need to be done if we want to support i8 or i16) rather than safety issue. So a sealed trait is proper here. Does this make sense? Or am I missing something? Regards, Boqun > Alice
Re: [RFC v2 02/13] rust: sync: Add basic atomic operation mapping framework
On Fri, Nov 1, 2024 at 7:03 AM Boqun Feng wrote: > > Preparation for generic atomic implementation. To unify the > ipmlementation of a generic method over `i32` and `i64`, the C side > atomic methods need to be grouped so that in a generic method, they can > be referred as ::, otherwise their parameters and return > value are different between `i32` and `i64`, which would require using > `transmute()` to unify the type into a `T`. > > Introduce `AtomicIpml` to represent a basic type in Rust that has the > direct mapping to an atomic implementation from C. This trait is sealed, > and currently only `i32` and `i64` ipml this. There seems to be quite a few instances of "impl" spelled as "ipml" here. > Further, different methods are put into different `*Ops` trait groups, > and this is for the future when smaller types like `i8`/`i16` are > supported but only with a limited set of API (e.g. only set(), load(), > xchg() and cmpxchg(), no add() or sub() etc). > > While the atomic mod is introduced, documentation is also added for > memory models and data races. > > Also bump my role to the maintainer of ATOMIC INFRASTRUCTURE to reflect > my responsiblity on the Rust atomic mod. > > Signed-off-by: Boqun Feng > --- > MAINTAINERS| 4 +- > rust/kernel/sync.rs| 1 + > rust/kernel/sync/atomic.rs | 19 > rust/kernel/sync/atomic/ops.rs | 199 + > 4 files changed, 222 insertions(+), 1 deletion(-) > create mode 100644 rust/kernel/sync/atomic.rs > create mode 100644 rust/kernel/sync/atomic/ops.rs > > diff --git a/MAINTAINERS b/MAINTAINERS > index b77f4495dcf4..e09471027a63 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -3635,7 +3635,7 @@ F:drivers/input/touchscreen/atmel_mxt_ts.c > ATOMIC INFRASTRUCTURE > M: Will Deacon > M: Peter Zijlstra > -R: Boqun Feng > +M: Boqun Feng > R: Mark Rutland > L: [email protected] > S: Maintained > @@ -3644,6 +3644,8 @@ 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/ This is why mod.rs files are superior :) > @@ -0,0 +1,19 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +//! Atomic primitives. > +//! > +//! These primitives have the same semantics as their C counterparts: and > the precise definitions of > +//! semantics can be found at [`LKMM`]. Note that Linux Kernel Memory > (Consistency) Model is the > +//! only model for Rust code in kernel, and Rust's own atomics should be > avoided. > +//! > +//! # Data races > +//! > +//! [`LKMM`] atomics have different rules regarding data races: > +//! > +//! - A normal read doesn't data-race with an atomic read. This was fixed: https://github.com/rust-lang/rust/pull/128778 > +mod private { > +/// Sealed trait marker to disable customized impls on atomic > implementation traits. > +pub trait Sealed {} > +} Just make the trait unsafe? Alice
