libitm: Fix privatization safety during upgrades to serial mode.

	libitm/
	* beginend.cc (GTM::gtm_thread::restart): Add and handle
	finish_serial_upgrade parameter.
	* libitm.h (GTM::gtm_thread::restart): Adapt declaration.
	* config/linux/rwlock.cc (GTM::gtm_rwlock::write_lock_generic):
	Don't unset reader flag.
	(GTM::gtm_rwlock::write_upgrade_finish): New.
	* config/posix/rwlock.cc: Same.
	* config/linux/rwlock.h (GTM::gtm_rwlock::write_upgrade_finish):
	Declare.
	* config/posix/rwlock.h: Same.
	* method-serial.cc (GTM::gtm_thread::serialirr_mode): Unset reader
	flag after commit or after rollback when restarting.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@182675 138bc75d-0d04-0410-961f-82ee72b054a4

2 files changed, 15 insertions, 6 deletions

diff --git a/libitm/config/linux/rwlock.cc b/libitm/config/linux/rwlock.cc
index f87be2e880a..24e7042ff10 100644
--- a/libitm/config/linux/rwlock.cc
+++ b/libitm/config/linux/rwlock.cc
@@ -121,17 +121,13 @@ gtm_rwlock::write_lock_generic (gtm_thread *tx)
   // readers that might still be active.
   // We don't need an extra barrier here because the CAS and the xchg
   // operations have full barrier semantics already.
-
-  // If this is an upgrade, we are not a reader anymore. This is only safe to
-  // do after we have acquired the writer lock.
   // TODO In the worst case, this requires one wait/wake pair for each
   // active reader. Reduce this!
-  if (tx != 0)
-    tx->shared_state.store (-1, memory_order_relaxed);
-
   for (gtm_thread *it = gtm_thread::list_of_threads; it != 0;
       it = it->next_thread)
     {
+      if (it == tx)
+        continue;
       // Use a loop here to check reader flags again after waiting.
       while (it->shared_state.load (memory_order_relaxed)
           != ~(typeof it->shared_state)0)
@@ -175,6 +171,18 @@ gtm_rwlock::write_upgrade (gtm_thread *tx)
 }
 
 
+// Has to be called iff the previous upgrade was successful and after it is
+// safe for the transaction to not be marked as a reader anymore.
+
+void
+gtm_rwlock::write_upgrade_finish (gtm_thread *tx)
+{
+  // We are not a reader anymore.  This is only safe to do after we have
+  // acquired the writer lock.
+  tx->shared_state.store (-1, memory_order_release);
+}
+
+
 // Release a RW lock from reading.
 
 void
diff --git a/libitm/config/linux/rwlock.h b/libitm/config/linux/rwlock.h
index e5a53c054f6..987e5801409 100644
--- a/libitm/config/linux/rwlock.h
+++ b/libitm/config/linux/rwlock.h
@@ -57,6 +57,7 @@ class gtm_rwlock
   void write_unlock ();
 
   bool write_upgrade (gtm_thread *tx);
+  void write_upgrade_finish (gtm_thread *tx);
 
  protected:
   bool write_lock_generic (gtm_thread *tx);