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

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<T>`, 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 <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260120115207.55318-3-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-11-boqun@kernel.org

1 files changed, 46 insertions, 0 deletions

diff --git a/rust/kernel/sync/atomic/predefine.rs b/rust/kernel/sync/atomic/predefine.rs
index ceb3caed9784..1d53834fcb12 100644
--- a/rust/kernel/sync/atomic/predefine.rs
+++ b/rust/kernel/sync/atomic/predefine.rs
@@ -178,6 +178,14 @@ mod tests {
 
             assert_eq!(v, x.load(Relaxed));
         });
+
+        for_each_type!(42 in [i8, i16, i32, i64, u32, u64, isize, usize] |v| {
+            let x = Atomic::new(v);
+            let ptr = x.as_ptr();
+
+            // SAFETY: `ptr` is a valid pointer and no concurrent access.
+            assert_eq!(v, unsafe { atomic_load(ptr, Relaxed) });
+        });
     }
 
     #[test]
@@ -188,6 +196,17 @@ mod tests {
             x.store(v, Release);
             assert_eq!(v, x.load(Acquire));
         });
+
+        for_each_type!(42 in [i8, i16, i32, i64, u32, u64, isize, usize] |v| {
+            let x = Atomic::new(0);
+            let ptr = x.as_ptr();
+
+            // SAFETY: `ptr` is a valid pointer and no concurrent access.
+            unsafe { atomic_store(ptr, v, Release) };
+
+            // SAFETY: `ptr` is a valid pointer and no concurrent access.
+            assert_eq!(v, unsafe { atomic_load(ptr, Acquire) });
+        });
     }
 
     #[test]
@@ -201,6 +220,18 @@ mod tests {
             assert_eq!(old, x.xchg(new, Full));
             assert_eq!(new, x.load(Relaxed));
         });
+
+        for_each_type!(42 in [i8, i16, i32, i64, u32, u64, isize, usize] |v| {
+            let x = Atomic::new(v);
+            let ptr = x.as_ptr();
+
+            let old = v;
+            let new = v + 1;
+
+            // SAFETY: `ptr` is a valid pointer and no concurrent access.
+            assert_eq!(old, unsafe { xchg(ptr, new, Full) });
+            assert_eq!(new, x.load(Relaxed));
+        });
     }
 
     #[test]
@@ -216,6 +247,21 @@ mod tests {
             assert_eq!(Ok(old), x.cmpxchg(old, new, Relaxed));
             assert_eq!(new, x.load(Relaxed));
         });
+
+        for_each_type!(42 in [i8, i16, i32, i64, u32, u64, isize, usize] |v| {
+            let x = Atomic::new(v);
+            let ptr = x.as_ptr();
+
+            let old = v;
+            let new = v + 1;
+
+            // SAFETY: `ptr` is a valid pointer and no concurrent access.
+            assert_eq!(Err(old), unsafe { cmpxchg(ptr, new, new, Full) });
+            assert_eq!(old, x.load(Relaxed));
+            // SAFETY: `ptr` is a valid pointer and no concurrent access.
+            assert_eq!(Ok(old), unsafe { cmpxchg(ptr, old, new, Relaxed) });
+            assert_eq!(new, x.load(Relaxed));
+        });
     }
 
     #[test]