ACPICA: Fix AcpiWalkNamespace race condition with table unload

Added a reader/writer locking mechanism to allow multiple
concurrent namespace walks (readers), but a dynamic table unload
will have exclusive access to the namespace. This fixes a problem
where a table unload could delete the portion of the namespace that
is currently being examined by a walk.  Adds a new file, utlock.c
that implements the reader/writer lock mechanism. ACPICA BZ 749.

http://www.acpica.org/bugzilla/show_bug.cgi?id=749

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 175 insertions, 0 deletions

diff --git a/drivers/acpi/acpica/utlock.c b/drivers/acpi/acpica/utlock.c
new file mode 100644
index 00000000000..25e03120686
--- /dev/null
+++ b/drivers/acpi/acpica/utlock.c
@@ -0,0 +1,175 @@
+/******************************************************************************
+ *
+ * Module Name: utlock - Reader/Writer lock interfaces
+ *
+ *****************************************************************************/
+
+/*
+ * Copyright (C) 2000 - 2009, Intel Corp.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions, and the following disclaimer,
+ *    without modification.
+ * 2. Redistributions in binary form must reproduce at minimum a disclaimer
+ *    substantially similar to the "NO WARRANTY" disclaimer below
+ *    ("Disclaimer") and any redistribution must be conditioned upon
+ *    including a substantially similar Disclaimer requirement for further
+ *    binary redistribution.
+ * 3. Neither the names of the above-listed copyright holders nor the names
+ *    of any contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * Alternatively, this software may be distributed under the terms of the
+ * GNU General Public License ("GPL") version 2 as published by the Free
+ * Software Foundation.
+ *
+ * NO WARRANTY
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGES.
+ */
+
+#include <acpi/acpi.h>
+#include "accommon.h"
+
+#define _COMPONENT          ACPI_UTILITIES
+ACPI_MODULE_NAME("utlock")
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ut_create_rw_lock
+ *              acpi_ut_delete_rw_lock
+ *
+ * PARAMETERS:  Lock                - Pointer to a valid RW lock
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Reader/writer lock creation and deletion interfaces.
+ *
+ ******************************************************************************/
+acpi_status acpi_ut_create_rw_lock(struct acpi_rw_lock *lock)
+{
+	acpi_status status;
+
+	lock->num_readers = 0;
+	status = acpi_os_create_mutex(&lock->reader_mutex);
+	if (ACPI_FAILURE(status)) {
+		return status;
+	}
+
+	status = acpi_os_create_mutex(&lock->writer_mutex);
+	return status;
+}
+
+void acpi_ut_delete_rw_lock(struct acpi_rw_lock *lock)
+{
+
+	acpi_os_delete_mutex(lock->reader_mutex);
+	acpi_os_delete_mutex(lock->writer_mutex);
+
+	lock->num_readers = 0;
+	lock->reader_mutex = NULL;
+	lock->writer_mutex = NULL;
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ut_acquire_read_lock
+ *              acpi_ut_release_read_lock
+ *
+ * PARAMETERS:  Lock                - Pointer to a valid RW lock
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Reader interfaces for reader/writer locks. On acquisition,
+ *              only the first reader acquires the write mutex. On release,
+ *              only the last reader releases the write mutex. Although this
+ *              algorithm can in theory starve writers, this should not be a
+ *              problem with ACPICA since the subsystem is infrequently used
+ *              in comparison to (for example) an I/O system.
+ *
+ ******************************************************************************/
+
+acpi_status acpi_ut_acquire_read_lock(struct acpi_rw_lock *lock)
+{
+	acpi_status status;
+
+	status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER);
+	if (ACPI_FAILURE(status)) {
+		return status;
+	}
+
+	/* Acquire the write lock only for the first reader */
+
+	lock->num_readers++;
+	if (lock->num_readers == 1) {
+		status =
+		    acpi_os_acquire_mutex(lock->writer_mutex,
+					  ACPI_WAIT_FOREVER);
+	}
+
+	acpi_os_release_mutex(lock->reader_mutex);
+	return status;
+}
+
+acpi_status acpi_ut_release_read_lock(struct acpi_rw_lock *lock)
+{
+	acpi_status status;
+
+	status = acpi_os_acquire_mutex(lock->reader_mutex, ACPI_WAIT_FOREVER);
+	if (ACPI_FAILURE(status)) {
+		return status;
+	}
+
+	/* Release the write lock only for the very last reader */
+
+	lock->num_readers--;
+	if (lock->num_readers == 0) {
+		acpi_os_release_mutex(lock->writer_mutex);
+	}
+
+	acpi_os_release_mutex(lock->reader_mutex);
+	return status;
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_ut_acquire_write_lock
+ *              acpi_ut_release_write_lock
+ *
+ * PARAMETERS:  Lock                - Pointer to a valid RW lock
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Writer interfaces for reader/writer locks. Simply acquire or
+ *              release the writer mutex associated with the lock. Acquisition
+ *              of the lock is fully exclusive and will block all readers and
+ *              writers until it is released.
+ *
+ ******************************************************************************/
+
+acpi_status acpi_ut_acquire_write_lock(struct acpi_rw_lock *lock)
+{
+	acpi_status status;
+
+	status = acpi_os_acquire_mutex(lock->writer_mutex, ACPI_WAIT_FOREVER);
+	return status;
+}
+
+void acpi_ut_release_write_lock(struct acpi_rw_lock *lock)
+{
+
+	acpi_os_release_mutex(lock->writer_mutex);
+}