On Tue, Jan 30, 2024 at 06:53:38AM -0800, Paul E. McKenney wrote:
> The ORDERING section of Documentation/atomic_t.txt can easily be read as
> saying that conditional atomic RMW operations that fail are ordered when
> those operations have the _acquire() or _release() prefixes. This is
> not the case, therefore update this section to make it clear that failed
> conditional atomic RMW operations provide no ordering.
>
> Reported-by: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> Cc: Andrea Parri <parri.andrea@xxxxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> Cc: David Howells <dhowells@xxxxxxxxxx>
> Cc: Jade Alglave <j.alglave@xxxxxxxxx>
> Cc: Luc Maranget <luc.maranget@xxxxxxxx>
> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> Cc: Akira Yokosawa <akiyks@xxxxxxxxx>
> Cc: Daniel Lustig <dlustig@xxxxxxxxxx>
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: <linux-arch@xxxxxxxxxxxxxxx>
> Cc: <linux-doc@xxxxxxxxxxxxxxx>
>
> diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
> index d7adc6d543db4..bee3b1bca9a7b 100644
> --- a/Documentation/atomic_t.txt
> +++ b/Documentation/atomic_t.txt
> @@ -171,14 +171,14 @@ The rule of thumb:
> - RMW operations that are conditional are unordered on FAILURE,
> otherwise the above rules apply.
>
> -Except of course when an operation has an explicit ordering like:
> +Except of course when a successful operation has an explicit ordering like:
>
> {}_relaxed: unordered
> {}_acquire: the R of the RMW (or atomic_read) is an ACQUIRE
> {}_release: the W of the RMW (or atomic_set) is a RELEASE
>
> Where 'unordered' is against other memory locations. Address dependencies are
> -not defeated.
> +not defeated. Conditional operations are still unordered on FAILURE.
>
> Fully ordered primitives are ordered against everything prior and everything
> subsequent. Therefore a fully ordered primitive is like having an smp_mb()
>
FWIW:
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Mark.
