libitm: Ensure proxy privatization safety.

	* method-gl.cc (gl_wt_dispatch::trycommit): Ensure proxy privatization
	safety.
	* method-ml.cc (ml_wt_dispatch::trycommit): Likewise.
	* libitm/testsuite/libitm.c/priv-1.c: New.

From-SVN: r232469

1 files changed, 116 insertions, 0 deletions

diff --git a/libitm/testsuite/libitm.c/priv-1.c b/libitm/testsuite/libitm.c/priv-1.c
new file mode 100644
index 0000000..635d523
--- /dev/null
+++ b/libitm/testsuite/libitm.c/priv-1.c
@@ -0,0 +1,116 @@
+/* Quick stress test for proxy privatization.  */
+
+/* We need to use a TM method that has to enforce privatization safety
+   explicitly.  */
+/* { dg-set-target-env-var ITM_DEFAULT_METHOD "ml_wt" } */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <pthread.h>
+
+/* Make them likely to be mapped to different orecs.  */
+#define ALIGN __attribute__((aligned (256)))
+/* Don't make these static to work around PR 68591.  */
+int x ALIGN;
+int *ptr ALIGN;
+int *priv_ptr ALIGN;
+int priv_value ALIGN;
+int barrier ALIGN = 0;
+const int iters = 100;
+
+static void arrive_and_wait (int expected_value)
+{
+  int now = __atomic_add_fetch (&barrier, 1, __ATOMIC_ACQ_REL);
+  while (now < expected_value)
+    __atomic_load (&barrier, &now, __ATOMIC_ACQUIRE);
+}
+
+static void __attribute__((transaction_pure,noinline)) delay (int i)
+{
+  for (volatile int v = 0; v < i; v++);
+}
+
+/* This tries to catch a case in which proxy privatization safety is not
+   ensured by privatization_user.  Specifically, it's access to the value
+   of it's transactional snapshot of ptr must read from an uncommitted write
+   by writer; thus, writer must still be active but must have read ptr before
+   proxy can privatize *ptr by assigning to ptr.
+   We try to make this interleaving more likely by delaying the commit of
+   writer and the start of proxy.  */
+static void *writer (void *dummy __attribute__((unused)))
+{
+  for (int i = 0; i < iters; i++)
+    {
+      /* Initialize state in each round.  */
+      x = 0;
+      ptr = &x;
+      priv_ptr = NULL;
+      int wrote = 1;
+      arrive_and_wait (i * 6 + 3);
+      /* Interference by another writer.  Has a conflict with the proxy
+	 privatizer.  */
+      __transaction_atomic
+	{
+	  if (ptr != NULL)
+	    *ptr = 1;
+	  else
+	    wrote = 0;
+	  delay (2000000);
+	}
+      arrive_and_wait (i * 6 + 6);
+      /* If the previous transaction committed first, wrote == 1 and x == 1;
+	 otherwise, if the proxy came first, wrote == 0 and priv_value == 0.
+       */
+      if (wrote != priv_value)
+	abort ();
+    }
+  return NULL;
+}
+
+static void *proxy (void *dummy __attribute__((unused)))
+{
+  for (int i = 0; i < iters; i++)
+    {
+      arrive_and_wait (i * 6 + 3);
+      delay(1000000);
+      __transaction_atomic
+	{
+	  /* Hand-off to privatization-user and its read-only transaction and
+	     subsequent use of privatization.  */
+	  priv_ptr = ptr;
+	  ptr = NULL;
+	}
+      arrive_and_wait (i * 6 + 6);
+    }
+  return NULL;
+}
+
+static void *privatization_user (void *dummy __attribute__((unused)))
+{
+  for (int i = 0; i < iters; i++)
+    {
+      arrive_and_wait (i * 6 + 3);
+      /* Spin until we have gotten a pointer from the proxy.  Then access
+	 the value pointed to nontransactionally.  */
+      int *p = NULL;
+      while (p == NULL)
+	__transaction_atomic { p = priv_ptr; }
+      priv_value = *p;
+      arrive_and_wait (i * 6 + 6);
+    }
+  return NULL;
+}
+
+int main()
+{
+  pthread_t p[3];
+
+  pthread_create (p+0, NULL, writer, NULL);
+  pthread_create (p+1, NULL, proxy, NULL);
+  pthread_create (p+2, NULL, privatization_user, NULL);
+
+  for (int i = 0; i < 3; ++i)
+    pthread_join  (p[i], NULL);
+
+  return 0;
+}