Implement a proper rw_tryupgrade

[mirror_spl.git] / module / spl / spl-rwlock.c

diff --git a/module/spl/spl-rwlock.c b/module/spl/spl-rwlock.c
index 98251c01154d6312b4d30ee8726e9e77ee67baec..9b356a843950218bfb4379ccce2ca82a6331b0a3 100644 (file)
--- a/module/spl/spl-rwlock.c
+++ b/module/spl/spl-rwlock.c
@@ -32,5 +32,46 @@
 
 #define DEBUG_SUBSYSTEM S_RWLOCK
 
+#ifdef 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);
+}
+#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) { }