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

Originally, `Atomic::from_ptr()` requires `T` being a `Sync` because I
thought having the ability to do `from_ptr()` meant multiplle
`&Atomic<T>`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<T>` 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 <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/20260120115207.55318-2-boqun.feng@gmail.com
Link: https://patch.msgid.link/20260303201701.12204-2-boqun@kernel.org

authored by

Boqun Feng and committed by
Peter Zijlstra 4a5dc632 0da9ca4c

+1 -4
+1 -4
rust/kernel/sync/atomic.rs
··· 204 204 /// // no data race. 205 205 /// unsafe { Atomic::from_ptr(foo_a_ptr) }.store(2, Release); 206 206 /// ``` 207 - pub unsafe fn from_ptr<'a>(ptr: *mut T) -> &'a Self 208 - where 209 - T: Sync, 210 - { 207 + pub unsafe fn from_ptr<'a>(ptr: *mut T) -> &'a Self { 211 208 // CAST: `T` and `Atomic<T>` have the same size, alignment and bit validity. 212 209 // SAFETY: Per function safety requirement, `ptr` is a valid pointer and the object will 213 210 // live long enough. It's safe to return a `&Atomic<T>` because function safety requirement