From d372e20433cbc0b0e3e59c89ccb6618501fcf6af Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 30 Jan 2024 06:08:32 -0800 Subject: [PATCH] Documentation/atomic_t: Emphasize that failed atomic operations give no ordering 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() suffixes. 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 Signed-off-by: Paul E. McKenney Cc: Alan Stern Cc: Will Deacon Cc: Peter Zijlstra Cc: Boqun Feng Cc: Nicholas Piggin Cc: David Howells Cc: Jade Alglave Cc: Luc Maranget Cc: "Paul E. McKenney" Cc: Akira Yokosawa Cc: Daniel Lustig Cc: Joel Fernandes Cc: Mark Rutland Cc: Jonathan Corbet Cc: Cc: Acked-by: Andrea Parri Acked-by: Mark Rutland --- Documentation/atomic_t.txt | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) 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() -- 2.30.2