The `impl Sync for LockedBy` implementation has insufficient trait bounds, as it only requires `T: Send`. However, `T: Sync` is also required for soundness because the `LockedBy::access` method could be used to provide shared access to the inner value from several threads in parallel.
Cc: stable@vger.kernel.org Fixes: 7b1f55e3a984 ("rust: sync: introduce `LockedBy`") Signed-off-by: Alice Ryhl aliceryhl@google.com --- rust/kernel/sync/locked_by.rs | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/rust/kernel/sync/locked_by.rs b/rust/kernel/sync/locked_by.rs index babc731bd5f6..153ba4edcb03 100644 --- a/rust/kernel/sync/locked_by.rs +++ b/rust/kernel/sync/locked_by.rs @@ -83,9 +83,10 @@ pub struct LockedBy<T: ?Sized, U: ?Sized> { // SAFETY: `LockedBy` can be transferred across thread boundaries iff the data it protects can. unsafe impl<T: ?Sized + Send, U: ?Sized> Send for LockedBy<T, U> {}
-// SAFETY: `LockedBy` serialises the interior mutability it provides, so it is `Sync` as long as the -// data it protects is `Send`. -unsafe impl<T: ?Sized + Send, U: ?Sized> Sync for LockedBy<T, U> {} +// SAFETY: Shared access to the `LockedBy` can provide both `&mut T` references in a synchronized +// manner, or `&T` access in an unsynchronized manner. The `Send` trait is sufficient for the first +// case, and `Sync` is sufficient for the second case. +unsafe impl<T: ?Sized + Send + Sync, U: ?Sized> Sync for LockedBy<T, U> {}
impl<T, U> LockedBy<T, U> { /// Constructs a new instance of [`LockedBy`]. @@ -127,7 +128,7 @@ pub fn access<'a>(&'a self, owner: &'a U) -> &'a T { panic!("mismatched owners"); }
- // SAFETY: `owner` is evidence that the owner is locked. + // SAFETY: `owner` is evidence that there are only shared references to the owner. unsafe { &*self.data.get() } }
--- base-commit: 93dc3be19450447a3a7090bd1dfb9f3daac3e8d2 change-id: 20240912-locked-by-sync-fix-07193df52f98
Best regards,