libports: use protected payloads to optimize the object lookup

* NEWS: Mention protected payloads.
* libports/Makefile (SRCS): Add `port-deref-deferred.c'.
* libports/create-internal.c (_ports_create_port_internal): Set the
protected payload to the objects address.
* libports/import-port.c (ports_import_port): Likewise.
* libports/reallocate-from-external.c (ports_reallocate_from_external):
Likewise.
* libports/reallocate-port.c (ports_reallocate_port): Likewise.
* libports/transfer-right.c (ports_transfer_right): Likewise.
* libports/manage-multithread.c (ports_manage_port_operations_multithread):
Use the protected payload for the object lookup if provided.  Add
thread pool management calls.
* libports/manage-one-thread.c (ports_manage_port_operations_one_thread):
Likewise.
* libports/destroy-right.c (ports_destroy_right): Defer the
dereferencing of outstanding send rights to avoid a port_info
use-after-free.
* libports/port-deref-deferred.c: New file.
* libports/port-deref-deferred.h: Likewise.
* libports/ports.h (struct port_bucket): New field `threadpool'.
(ports_lookup_payload): Check `port_right'.

1 files changed, 89 insertions, 0 deletions

diff --git a/libports/port-deref-deferred.h b/libports/port-deref-deferred.h
new file mode 100644
index 00000000..1589cb20
--- /dev/null
+++ b/libports/port-deref-deferred.h
@@ -0,0 +1,89 @@
+/* Delayed deallocation of port_info objects.
+
+   Copyright (C) 2015 Free Software Foundation, Inc.
+
+   Written by Justus Winter <4winter@informatik.uni-hamburg.de>
+
+   This file is part of the GNU Hurd.
+
+   The GNU Hurd is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2, or (at
+   your option) any later version.
+
+   The GNU Hurd 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
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with the GNU Hurd.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef	_HURD_PORTS_DEREF_DEFERRED_
+#define	_HURD_PORTS_DEREF_DEFERRED_
+
+#include <pthread.h>
+
+/* A list of port_info objects.  */
+struct pi_list;
+
+/* We use protected payloads to look up objects without taking a lock.
+   A complication arises if we destroy an object using
+   ports_destroy_right.  To avoid payloads from becoming stale (and
+   resulting in invalid memory accesses when being interpreted as
+   pointer), we delay the deallocation of those object until all
+   threads running at the time of the objects destruction are done
+   with whatever they were doing and entered a quiescent period.  */
+struct ports_threadpool
+{
+  /* Access to the threadpool object is serialized by this lock.  */
+  pthread_spinlock_t lock;
+
+  /* We maintain two sets of objects and threads.  Each thread and the
+     threadpool itself has a color.  If a thread has the same color as
+     the thread pool, it belongs to the old generation.  */
+  unsigned int color;
+
+  /* The number of old threads.  When an old thread enters its
+     quiescent period, it decrements OLD_THREADS and flips its color
+     (hence becoming a young thread).  */
+  size_t old_threads;
+
+  /* A list of old objects.  Once OLD_THREADS drops to zero, they are
+     deallocated, and all young threads and objects become old threads
+     and objects.  */
+  struct pi_list *old_objects;
+
+  /* The number of young threads.  Any thread joining or leaving the
+     thread group must be a young thread.  */
+  size_t young_threads;
+
+  /* The list of young objects.  Any object being marked for delayed
+     deallocation is added to this list.  */
+  struct pi_list *young_objects;
+};
+
+/* Per-thread state.  */
+struct ports_thread
+{
+  unsigned int color;
+};
+
+/* Initialize the thread pool.  */
+void _ports_threadpool_init (struct ports_threadpool *);
+
+/* Called by a thread to join a thread pool.  */
+void _ports_thread_online (struct ports_threadpool *, struct ports_thread *);
+
+/* Called by a thread that enters its quiescent period.  */
+void _ports_thread_quiescent (struct ports_threadpool *, struct ports_thread *);
+
+/* Called by a thread to leave a thread pool.  */
+void _ports_thread_offline (struct ports_threadpool *, struct ports_thread *);
+
+struct port_info;
+
+/* Schedule an object for deallocation.  */
+void _ports_port_deref_deferred (struct port_info *);
+
+#endif	/* _HURD_PORTS_DEREF_DEFERRED_ */