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Documentation/atomic_t: Emphasize that failed atomic operations give no ordering

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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 <anna-maria@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jade Alglave <j.alglave@ucl.ac.uk>
Cc: Luc Maranget <luc.maranget@inria.fr>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Akira Yokosawa <akiyks@gmail.com>
Cc: Daniel Lustig <dlustig@nvidia.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: <linux-arch@vger.kernel.org>
Cc: <linux-doc@vger.kernel.org>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
This commit is contained in:
Paul E. McKenney 2024-01-30 06:08:32 -08:00
parent 293f5bc271
commit d372e20433
1 changed files with 2 additions and 2 deletions
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Documentation/atomic_t.txt
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@ -171,14 +171,14 @@ The rule of thumb:
- RMW operations that are conditional are unordered on FAILURE, - RMW operations that are conditional are unordered on FAILURE,
otherwise the above rules apply. 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 {}_relaxed: unordered
{}_acquire: the R of the RMW (or atomic_read) is an ACQUIRE {}_acquire: the R of the RMW (or atomic_read) is an ACQUIRE
{}_release: the W of the RMW (or atomic_set) is a RELEASE {}_release: the W of the RMW (or atomic_set) is a RELEASE
Where 'unordered' is against other memory locations. Address dependencies are 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 Fully ordered primitives are ordered against everything prior and everything
subsequent. Therefore a fully ordered primitive is like having an smp_mb() subsequent. Therefore a fully ordered primitive is like having an smp_mb()