Resguardo inicial

linux-7.2.3/Documentation/litmus-tests/README

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

linux-7.2.3/Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus

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+C Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
+
+(*
+ * Result: Never
+ *
+ * Test that an atomic RMW followed by a smp_mb__after_atomic() is
+ * stronger than a normal acquire: both the read and write parts of
+ * the RMW are ordered before the subsequential memory accesses.
+ *)
+
+{
+}
+
+P0(int *x, atomic_t *y)
+{
+	int r0;
+	int r1;
+
+	r0 = READ_ONCE(*x);
+	smp_rmb();
+	r1 = atomic_read(y);
+}
+
+P1(int *x, atomic_t *y)
+{
+	atomic_inc(y);
+	smp_mb__after_atomic();
+	WRITE_ONCE(*x, 1);
+}
+
+exists
+(0:r0=1 /\ 0:r1=0)

linux-7.2.3/Documentation/litmus-tests/atomic/Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus

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+C Atomic-RMW-ops-are-atomic-WRT-atomic_set
+
+(*
+ * Result: Never
+ *
+ * Test that atomic_set() cannot break the atomicity of atomic RMWs.
+ * NOTE: This requires herd7 7.56 or later which supports "(void)expr".
+ *)
+
+{
+	atomic_t v = ATOMIC_INIT(1);
+}
+
+P0(atomic_t *v)
+{
+	(void)atomic_add_unless(v, 1, 0);
+}
+
+P1(atomic_t *v)
+{
+	atomic_set(v, 0);
+}
+
+exists
+(v=2)

linux-7.2.3/Documentation/litmus-tests/atomic/cmpxchg-fail-ordered-1.litmus

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+C cmpxchg-fail-ordered-1
+
+(*
+ * Result: Never
+ *
+ * Demonstrate that a failing cmpxchg() operation will act as a full
+ * barrier when followed by smp_mb__after_atomic().
+ *)
+
+{}
+
+P0(int *x, int *y, int *z)
+{
+	int r0;
+	int r1;
+
+	WRITE_ONCE(*x, 1);
+	r1 = cmpxchg(z, 1, 0);
+	smp_mb__after_atomic();
+	r0 = READ_ONCE(*y);
+}
+
+P1(int *x, int *y, int *z)
+{
+	int r0;
+	int r1;
+
+	WRITE_ONCE(*y, 1);
+	r1 = cmpxchg(z, 1, 0);
+	smp_mb__after_atomic();
+	r0 = READ_ONCE(*x);
+}
+
+locations[0:r1;1:r1]
+exists (0:r0=0 /\ 1:r0=0)

linux-7.2.3/Documentation/litmus-tests/atomic/cmpxchg-fail-ordered-2.litmus

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+C cmpxchg-fail-ordered-2
+
+(*
+ * Result: Never
+ *
+ * Demonstrate use of smp_mb__after_atomic() to make a failing cmpxchg
+ * operation have acquire ordering.
+ *)
+
+{}
+
+P0(int *x, int *y)
+{
+	int r1;
+
+	WRITE_ONCE(*x, 1);
+	r1 = cmpxchg(y, 0, 1);
+}
+
+P1(int *x, int *y)
+{
+	int r1;
+	int r2;
+
+	r1 = cmpxchg(y, 0, 1);
+	smp_mb__after_atomic();
+	r2 = READ_ONCE(*x);
+}
+
+exists (0:r1=0 /\ 1:r1=1 /\ 1:r2=0)

linux-7.2.3/Documentation/litmus-tests/atomic/cmpxchg-fail-unordered-1.litmus

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+C cmpxchg-fail-unordered-1
+
+(*
+ * Result: Sometimes
+ *
+ * Demonstrate that a failing cmpxchg() operation does not act as a
+ * full barrier.  (In contrast, a successful cmpxchg() does act as a
+ * full barrier.)
+ *)
+
+{}
+
+P0(int *x, int *y, int *z)
+{
+	int r0;
+	int r1;
+
+	WRITE_ONCE(*x, 1);
+	r1 = cmpxchg(z, 1, 0);
+	r0 = READ_ONCE(*y);
+}
+
+P1(int *x, int *y, int *z)
+{
+	int r0;
+	int r1;
+
+	WRITE_ONCE(*y, 1);
+	r1 = cmpxchg(z, 1, 0);
+	r0 = READ_ONCE(*x);
+}
+
+locations[0:r1;1:r1]
+exists (0:r0=0 /\ 1:r0=0)

linux-7.2.3/Documentation/litmus-tests/atomic/cmpxchg-fail-unordered-2.litmus

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+C cmpxchg-fail-unordered-2
+
+(*
+ * Result: Sometimes
+ *
+ * Demonstrate that a failing cmpxchg() operation does not act as either
+ * an acquire release operation.  (In contrast, a successful cmpxchg()
+ * does act as both an acquire and a release operation.)
+ *)
+
+{}
+
+P0(int *x, int *y)
+{
+	int r1;
+
+	WRITE_ONCE(*x, 1);
+	r1 = cmpxchg(y, 0, 1);
+}
+
+P1(int *x, int *y)
+{
+	int r1;
+	int r2;
+
+	r1 = cmpxchg(y, 0, 1);
+	r2 = READ_ONCE(*x);
+}
+
+exists (0:r1=0 /\ 1:r1=1 /\ 1:r2=0)

linux-7.2.3/Documentation/litmus-tests/locking/DCL-broken.litmus

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+C DCL-broken
+
+(*
+ * Result: Sometimes
+ *
+ * This litmus test demonstrates more than just locking is required to
+ * correctly implement double-checked locking.
+ *)
+
+{
+	int flag;
+	int data;
+}
+
+P0(int *flag, int *data, spinlock_t *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = READ_ONCE(*flag);
+	if (r0 == 0) {
+		spin_lock(lck);
+		r1 = READ_ONCE(*flag);
+		if (r1 == 0) {
+			WRITE_ONCE(*data, 1);
+			WRITE_ONCE(*flag, 1);
+		}
+		spin_unlock(lck);
+	}
+	r2 = READ_ONCE(*data);
+}
+
+P1(int *flag, int *data, spinlock_t *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = READ_ONCE(*flag);
+	if (r0 == 0) {
+		spin_lock(lck);
+		r1 = READ_ONCE(*flag);
+		if (r1 == 0) {
+			WRITE_ONCE(*data, 1);
+			WRITE_ONCE(*flag, 1);
+		}
+		spin_unlock(lck);
+	}
+	r2 = READ_ONCE(*data);
+}
+
+locations [flag;data;0:r0;0:r1;1:r0;1:r1]
+exists (0:r2=0 \/ 1:r2=0)

linux-7.2.3/Documentation/litmus-tests/locking/DCL-fixed.litmus

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+C DCL-fixed
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that double-checked locking can be
+ * reliable given proper use of smp_load_acquire() and smp_store_release()
+ * in addition to the locking.
+ *)
+
+{
+	int flag;
+	int data;
+}
+
+P0(int *flag, int *data, spinlock_t *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = smp_load_acquire(flag);
+	if (r0 == 0) {
+		spin_lock(lck);
+		r1 = READ_ONCE(*flag);
+		if (r1 == 0) {
+			WRITE_ONCE(*data, 1);
+			smp_store_release(flag, 1);
+		}
+		spin_unlock(lck);
+	}
+	r2 = READ_ONCE(*data);
+}
+
+P1(int *flag, int *data, spinlock_t *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = smp_load_acquire(flag);
+	if (r0 == 0) {
+		spin_lock(lck);
+		r1 = READ_ONCE(*flag);
+		if (r1 == 0) {
+			WRITE_ONCE(*data, 1);
+			smp_store_release(flag, 1);
+		}
+		spin_unlock(lck);
+	}
+	r2 = READ_ONCE(*data);
+}
+
+locations [flag;data;0:r0;0:r1;1:r0;1:r1]
+exists (0:r2=0 \/ 1:r2=0)

linux-7.2.3/Documentation/litmus-tests/locking/RM-broken.litmus

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+C RM-broken
+
+(*
+ * Result: DEADLOCK
+ *
+ * This litmus test demonstrates that the old "roach motel" approach
+ * to locking, where code can be freely moved into critical sections,
+ * cannot be used in the Linux kernel.
+ *)
+
+{
+	int x;
+	atomic_t y;
+}
+
+P0(int *x, atomic_t *y, spinlock_t *lck)
+{
+	int r2;
+
+	spin_lock(lck);
+	r2 = atomic_inc_return(y);
+	WRITE_ONCE(*x, 1);
+	spin_unlock(lck);
+}
+
+P1(int *x, atomic_t *y, spinlock_t *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	spin_lock(lck);
+	r0 = READ_ONCE(*x);
+	r1 = READ_ONCE(*x);
+	r2 = atomic_inc_return(y);
+	spin_unlock(lck);
+}
+
+locations [x;0:r2;1:r0;1:r1;1:r2]
+filter (1:r0=0 /\ 1:r1=1)
+exists (1:r2=1)

linux-7.2.3/Documentation/litmus-tests/locking/RM-fixed.litmus

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+C RM-fixed
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that the old "roach motel" approach
+ * to locking, where code can be freely moved into critical sections,
+ * cannot be used in the Linux kernel.
+ *)
+
+{
+	int x;
+	atomic_t y;
+}
+
+P0(int *x, atomic_t *y, spinlock_t *lck)
+{
+	int r2;
+
+	spin_lock(lck);
+	r2 = atomic_inc_return(y);
+	WRITE_ONCE(*x, 1);
+	spin_unlock(lck);
+}
+
+P1(int *x, atomic_t *y, spinlock_t *lck)
+{
+	int r0;
+	int r1;
+	int r2;
+
+	r0 = READ_ONCE(*x);
+	r1 = READ_ONCE(*x);
+	spin_lock(lck);
+	r2 = atomic_inc_return(y);
+	spin_unlock(lck);
+}
+
+locations [x;0:r2;1:r0;1:r1;1:r2]
+filter (1:r0=0 /\ 1:r1=1)
+exists (1:r2=1)

linux-7.2.3/Documentation/litmus-tests/rcu/RCU+sync+free.litmus

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+C RCU+sync+free
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that an RCU reader can never see a write that
+ * follows a grace period, if it did not see writes that precede that grace
+ * period.
+ *
+ * This is a typical pattern of RCU usage, where the write before the grace
+ * period assigns a pointer, and the writes following the grace period destroy
+ * the object that the pointer used to point to.
+ *
+ * This is one implication of the RCU grace-period guarantee, which says (among
+ * other things) that an RCU read-side critical section cannot span a grace period.
+ *)
+
+{
+int x = 1;
+int *y = &x;
+int z = 1;
+}
+
+P0(int *x, int *z, int **y)
+{
+	int *r0;
+	int r1;
+
+	rcu_read_lock();
+	r0 = rcu_dereference(*y);
+	r1 = READ_ONCE(*r0);
+	rcu_read_unlock();
+}
+
+P1(int *x, int *z, int **y)
+{
+	rcu_assign_pointer(*y, z);
+	synchronize_rcu();
+	WRITE_ONCE(*x, 0);
+}
+
+exists (0:r0=x /\ 0:r1=0)

linux-7.2.3/Documentation/litmus-tests/rcu/RCU+sync+read.litmus

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+C RCU+sync+read
+
+(*
+ * Result: Never
+ *
+ * This litmus test demonstrates that after a grace period, an RCU updater always
+ * sees all stores done in prior RCU read-side critical sections. Such
+ * read-side critical sections would have ended before the grace period ended.
+ *
+ * This is one implication of the RCU grace-period guarantee, which says (among
+ * other things) that an RCU read-side critical section cannot span a grace period.
+ *)
+
+{
+int x = 0;
+int y = 0;
+}
+
+P0(int *x, int *y)
+{
+	rcu_read_lock();
+	WRITE_ONCE(*x, 1);
+	WRITE_ONCE(*y, 1);
+	rcu_read_unlock();
+}
+
+P1(int *x, int *y)
+{
+	int r0;
+	int r1;
+
+	r0 = READ_ONCE(*x);
+	synchronize_rcu();
+	r1 = READ_ONCE(*y);
+}
+
+exists (1:r0=1 /\ 1:r1=0)