linux.git/rust/kernel/sync/atomic.rs, branch v7.1-rc2

rust: sync: atomic: Update documentation for `fetch_add()`

2026-03-08T10:06:51+00:00

The documentation for `fetch_add()` does not indicate that the original
value is returned by `fetch_add()`. Update the documentation so this is
clear.

Signed-off-by: Andreas Hindborg 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alice Ryhl 
Link: https://patch.msgid.link/20260220-atomic-sub-v3-2-e63cbed1d2aa@kernel.org
Link: https://patch.msgid.link/20260303201701.12204-13-boqun@kernel.org

rust: sync: atomic: Add fetch_sub()

2026-03-08T10:06:50+00:00

Add `Atomic::fetch_sub()` with implementation and documentation in line
with existing `Atomic::fetch_add()` implementation.

Signed-off-by: Andreas Hindborg 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alice Ryhl 
Link: https://patch.msgid.link/20260220-atomic-sub-v3-1-e63cbed1d2aa@kernel.org
Link: https://patch.msgid.link/20260303201701.12204-12-boqun@kernel.org

rust: sync: atomic: Add atomic operation helpers over raw pointers

2026-03-08T10:06:50+00:00

In order to synchronize with C or external memory, atomic operations
over raw pointers are need. Although there is already an
`Atomic::from_ptr()` to provide a `&Atomic`, it's more convenient to
have helpers that directly perform atomic operations on raw pointers.
Hence a few are added, which are basically an `Atomic::from_ptr().op()`
wrapper.

Note: for naming, since `atomic_xchg()` and `atomic_cmpxchg()` have a
conflict naming to 32bit C atomic xchg/cmpxchg, hence the helpers are
just named as `xchg()` and `cmpxchg()`. For `atomic_load()` and
`atomic_store()`, their 32bit C counterparts are `atomic_read()` and
`atomic_set()`, so keep the `atomic_` prefix.

[boqun: Fix typo spotted by Alice and fix broken sentence spotted by
Gary]

Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alice Ryhl 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260120115207.55318-3-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-11-boqun@kernel.org

rust: sync: atomic: Add performance-optimal Flag type for atomic booleans

2026-03-08T10:06:49+00:00

Add AtomicFlag type for boolean flags.

Document when AtomicFlag is generally preferable to Atomic: in
particular, when RMW operations such as xchg()/cmpxchg() may be used
and minimizing memory usage is not the top priority. On some
architectures without byte-sized RMW instructions, Atomic can be
slower for RMW operations.

Signed-off-by: FUJITA Tomonori 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260129122622.3896144-2-tomo@aliasing.net
Link: https://patch.msgid.link/20260303201701.12204-9-boqun@kernel.org

rust: sync: atomic: Add Atomic<*{mut,const} T> support

2026-03-08T10:06:49+00:00

Atomic pointer support is an important piece of synchronization
algorithm, e.g. RCU, hence provide the support for that.

Note that instead of relying on atomic_long or the implementation of
`Atomic`, a new set of helpers (atomic_ptr_*) is introduced for
atomic pointer specifically, this is because ptr2int casting would
lose the provenance of a pointer and even though in theory there are a
few tricks the provenance can be restored, it'll still be a simpler
implementation if C could provide atomic pointers directly. The side
effects of this approach are: we don't have the arithmetic and logical
operations for pointers yet and the current implementation only works
on ARCH_SUPPORTS_ATOMIC_RMW architectures, but these are implementation
issues and can be added later.

Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Gary Guo 
Reviewed-by: FUJITA Tomonori 
Link: https://patch.msgid.link/20260120140503.62804-3-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-8-boqun@kernel.org

rust: sync: atomic: Add example for Atomic::get_mut()

2026-03-08T10:06:48+00:00

Add an example for Atomic::get_mut(). No functional change.

Signed-off-by: FUJITA Tomonori 
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alice Ryhl 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260128123313.3850604-1-tomo@aliasing.net
Link: https://patch.msgid.link/20260303201701.12204-3-boqun@kernel.org

rust: sync: atomic: Remove bound `T: Sync` for `Atomic::from_ptr()`

2026-03-08T10:06:47+00:00

Originally, `Atomic::from_ptr()` requires `T` being a `Sync` because I
thought having the ability to do `from_ptr()` meant multiplle
`&Atomic`s shared by different threads, which was identical (or
similar) to multiple `&T`s shared by different threads. Hence `T` was
required to be `Sync`. However this is not true, since `&Atomic` is
not the same at `&T`. Moreover, having this bound makes `Atomic::<*mut
T>::from_ptr()` impossible, which is definitely not intended. Therefore
remove the `T: Sync` bound.

[boqun: Fix title typo spotted by Alice & Gary]

Fixes: 29c32c405e53 ("rust: sync: atomic: Add generic atomics")
Signed-off-by: Boqun Feng 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Alice Ryhl 
Reviewed-by: Gary Guo 
Link: https://patch.msgid.link/20260120115207.55318-2-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-2-boqun@kernel.org

rust: sync: atomic: separate import "blocks"

2025-12-06T16:44:10+00:00

Commit 14e9a18b07ec ("rust: sync: atomic: Make Atomic*Ops pub(crate)")
added a `pub(crate)` import in the same "block" as the `pub` one,
without running `rustfmt`, which would sort them differently.

Instead of running `rustfmt` as-is, add a newline to keep the import
"blocks" with different visibilities separate.

Signed-off-by: Miguel Ojeda 
Signed-off-by: Linus Torvalds

rust: sync: atomic: Implement Debug for Atomic

2025-11-12T16:56:41+00:00

If `Atomic` is `Debug` then it's a `debugfs::Writer`, therefore make
it so since 1) debugfs needs to support `Atomic` and 2) it's rather
trivial to implement `Debug` for `Atomic`.

Tested-by: David Gow 
Acked-by: Greg Kroah-Hartman 
Signed-off-by: Boqun Feng 
Link: https://patch.msgid.link/20251022035324.70785-3-boqun.feng@gmail.com

rust: sync: atomic: Make Atomic*Ops pub(crate)

2025-11-12T16:56:38+00:00

In order to write code over a generate Atomic we need to make
Atomic*Ops public so that functions like `.load()` and `.store()` are
available. Make these pub(crate) at the beginning so the usage in kernel
crate is supported.

Tested-by: David Gow 
Acked-by: Greg Kroah-Hartman 
Signed-off-by: Boqun Feng 
Link: https://patch.msgid.link/20251022035324.70785-2-boqun.feng@gmail.com