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This commit adds four litmus tests showing that a failing cmpxchg() operation is unordered unless followed by an smp_mb__after_atomic() operation. Suggested-by: Frederic Weisbecker <frederic@kernel.org> 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>
81 lines
2.9 KiB
Plaintext
81 lines
2.9 KiB
Plaintext
============
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LITMUS TESTS
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============
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Each subdirectory contains litmus tests that are typical to describe the
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semantics of respective kernel APIs.
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For more information about how to "run" a litmus test or how to generate
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a kernel test module based on a litmus test, please see
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tools/memory-model/README.
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atomic (/atomic directory)
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--------------------------
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Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
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Test that an atomic RMW followed by a smp_mb__after_atomic() is
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stronger than a normal acquire: both the read and write parts of
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the RMW are ordered before the subsequential memory accesses.
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Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
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Test that atomic_set() cannot break the atomicity of atomic RMWs.
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NOTE: Require herd7 7.56 or later which supports "(void)expr".
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cmpxchg-fail-ordered-1.litmus
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Demonstrate that a failing cmpxchg() operation acts as a full barrier
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when followed by smp_mb__after_atomic().
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cmpxchg-fail-ordered-2.litmus
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Demonstrate that a failing cmpxchg() operation acts as an acquire
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operation when followed by smp_mb__after_atomic().
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cmpxchg-fail-unordered-1.litmus
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Demonstrate that a failing cmpxchg() operation does not act as a
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full barrier.
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cmpxchg-fail-unordered-2.litmus
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Demonstrate that a failing cmpxchg() operation does not act as an
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acquire operation.
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locking (/locking directory)
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----------------------------
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DCL-broken.litmus
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Demonstrates that double-checked locking needs more than just
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the obvious lock acquisitions and releases.
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DCL-fixed.litmus
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Demonstrates corrected double-checked locking that uses
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smp_store_release() and smp_load_acquire() in addition to the
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obvious lock acquisitions and releases.
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RM-broken.litmus
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Demonstrates problems with "roach motel" locking, where code is
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freely moved into lock-based critical sections. This example also
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shows how to use the "filter" clause to discard executions that
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would be excluded by other code not modeled in the litmus test.
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Note also that this "roach motel" optimization is emulated by
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physically moving P1()'s two reads from x under the lock.
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What is a roach motel? This is from an old advertisement for
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a cockroach trap, much later featured in one of the "Men in
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Black" movies. "The roaches check in. They don't check out."
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RM-fixed.litmus
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The counterpart to RM-broken.litmus, showing P0()'s two loads from
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x safely outside of the critical section.
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RCU (/rcu directory)
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--------------------
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MP+onceassign+derefonce.litmus (under tools/memory-model/litmus-tests/)
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Demonstrates the use of rcu_assign_pointer() and rcu_dereference() to
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ensure that an RCU reader will not see pre-initialization garbage.
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RCU+sync+read.litmus
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RCU+sync+free.litmus
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Both the above litmus tests demonstrate the RCU grace period guarantee
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that an RCU read-side critical section can never span a grace period.
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