1 files changed, 114 insertions, 0 deletions
diff --git a/module/spl/spl-rwlock.c b/module/spl/spl-rwlock.c
new file mode 100644
index 000000000..9a992cc3a
--- /dev/null
+++ b/module/spl/spl-rwlock.c
@@ -0,0 +1,114 @@
+/*
+ *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
+ *  Copyright (C) 2007 The Regents of the University of California.
+ *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
+ *  Written by Brian Behlendorf <[email protected]>.
+ *  UCRL-CODE-235197
+ *
+ *  This file is part of the SPL, Solaris Porting Layer.
+ *  For details, see <http://zfsonlinux.org/>.
+ *
+ *  The SPL 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 of the License, or (at your
+ *  option) any later version.
+ *
+ *  The SPL 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 SPL.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *  Solaris Porting Layer (SPL) Reader/Writer Lock Implementation.
+ */
+
+#include <sys/rwlock.h>
+
+#if defined(CONFIG_PREEMPT_RT_FULL)
+
+#include <linux/rtmutex.h>
+#define	RT_MUTEX_OWNER_MASKALL	1UL
+
+static int
+__rwsem_tryupgrade(struct rw_semaphore *rwsem)
+{
+
+	ASSERT((struct task_struct *)
+	    ((unsigned long)rwsem->lock.owner & ~RT_MUTEX_OWNER_MASKALL) ==
+	    current);
+
+	/*
+	 * Under the realtime patch series, rwsem is implemented as a
+	 * single mutex held by readers and writers alike. However,
+	 * this implementation would prevent a thread from taking a
+	 * read lock twice, as the mutex would already be locked on
+	 * the second attempt. Therefore the implementation allows a
+	 * single thread to take a rwsem as read lock multiple times
+	 * tracking that nesting as read_depth counter.
+	 */
+	if (rwsem->read_depth <= 1) {
+		/*
+		 * In case, the current thread has not taken the lock
+		 * more than once as read lock, we can allow an
+		 * upgrade to a write lock. rwsem_rt.h implements
+		 * write locks as read_depth == 0.
+		 */
+		rwsem->read_depth = 0;
+		return (1);
+	}
+	return (0);
+}
+#elif defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
+static int
+__rwsem_tryupgrade(struct rw_semaphore *rwsem)
+{
+	int ret = 0;
+	unsigned long flags;
+	spl_rwsem_lock_irqsave(&rwsem->wait_lock, flags);
+	if (RWSEM_COUNT(rwsem) == SPL_RWSEM_SINGLE_READER_VALUE &&
+	    list_empty(&rwsem->wait_list)) {
+		ret = 1;
+		RWSEM_COUNT(rwsem) = SPL_RWSEM_SINGLE_WRITER_VALUE;
+	}
+	spl_rwsem_unlock_irqrestore(&rwsem->wait_lock, flags);
+	return (ret);
+}
+#elif defined(HAVE_RWSEM_ATOMIC_LONG_COUNT)
+static int
+__rwsem_tryupgrade(struct rw_semaphore *rwsem)
+{
+	long val;
+	val = atomic_long_cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE,
+	    SPL_RWSEM_SINGLE_WRITER_VALUE);
+	return (val == SPL_RWSEM_SINGLE_READER_VALUE);
+}
+#else
+static int
+__rwsem_tryupgrade(struct rw_semaphore *rwsem)
+{
+	typeof(rwsem->count) val;
+	val = cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE,
+	    SPL_RWSEM_SINGLE_WRITER_VALUE);
+	return (val == SPL_RWSEM_SINGLE_READER_VALUE);
+}
+#endif
+
+int
+rwsem_tryupgrade(struct rw_semaphore *rwsem)
+{
+	if (__rwsem_tryupgrade(rwsem)) {
+		rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
+		rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
+#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
+		rwsem->owner = current;
+#endif
+		return (1);
+	}
+	return (0);
+}
+EXPORT_SYMBOL(rwsem_tryupgrade);
+
+int spl_rw_init(void) { return 0; }
+void spl_rw_fini(void) { }