Prepare for radical source tree reorganization. zack/build-layout-experiment

All top-level files and directories are moved into a temporary storage
directory, REORG.TODO, except for files that will certainly still
exist in their current form at top level when we're done (COPYING,
COPYING.LIB, LICENSES, NEWS, README), all old ChangeLog files (which
are moved to the new directory OldChangeLogs, instead), and the
generated file INSTALL (which is just deleted; in the new order, there
will be no generated files checked into version control).

1 files changed, 61 insertions, 0 deletions

diff --git a/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-unlock.c b/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-unlock.c
new file mode 100644
index 0000000000..c062d71b77
--- /dev/null
+++ b/REORG.TODO/sysdeps/unix/sysv/linux/s390/elision-unlock.c
@@ -0,0 +1,61 @@
+/* Commit an elided pthread lock.
+   Copyright (C) 2014-2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <pthreadP.h>
+#include <lowlevellock.h>
+#include <htm.h>
+
+int
+__lll_unlock_elision(int *futex, short *adapt_count, int private)
+{
+  /* If the lock is free, we elided the lock earlier.  This does not
+     necessarily mean that we are in a transaction, because the user code may
+     have closed the transaction, but that is impossible to detect reliably.
+     Relaxed MO access to futex is sufficient because a correct program
+     will only release a lock it has acquired; therefore, it must either
+     changed the futex word's value to something !=0 or it must have used
+     elision; these are actions by the same thread, so these actions are
+     sequenced-before the relaxed load (and thus also happens-before the
+     relaxed load).  Therefore, relaxed MO is sufficient.  */
+  if (atomic_load_relaxed (futex) == 0)
+    {
+      __libc_tend ();
+    }
+  else
+    {
+      /* Update the adapt_count while unlocking before completing the critical
+	 section.  adapt_count is accessed concurrently outside of a
+	 transaction or a critical section (e.g. in elision-lock.c). So we need
+	 to use atomic accesses.  However, the value of adapt_count is just a
+	 hint, so relaxed MO accesses are sufficient.
+	 If adapt_count would be decremented while locking, multiple
+	 CPUs, trying to lock the acquired mutex, will decrement adapt_count to
+	 zero and another CPU will try to start a transaction, which will be
+	 immediately aborted as the mutex is locked.
+	 The update of adapt_count is done before releasing the lock as POSIX'
+	 mutex destruction requirements disallow accesses to the mutex after it
+	 has been released and thus could have been acquired or destroyed by
+	 another thread.  */
+      short adapt_count_val = atomic_load_relaxed (adapt_count);
+      if (adapt_count_val > 0)
+	atomic_store_relaxed (adapt_count, adapt_count_val - 1);
+
+      lll_unlock ((*futex), private);
+    }
+  return 0;
+}