Add the rt linux 4.1.3-rt3 as base

[kvmfornfv.git] / kernel / include / asm-generic / mutex-xchg.h

diff --git a/kernel/include/asm-generic/mutex-xchg.h b/kernel/include/asm-generic/mutex-xchg.h
new file mode 100644 (file)
index 0000000..f169ec0
--- /dev/null
+++ b/kernel/include/asm-generic/mutex-xchg.h
@@ -0,0 +1,116 @@
+/*
+ * include/asm-generic/mutex-xchg.h
+ *
+ * Generic implementation of the mutex fastpath, based on xchg().
+ *
+ * NOTE: An xchg based implementation might be less optimal than an atomic
+ *       decrement/increment based implementation. If your architecture
+ *       has a reasonable atomic dec/inc then you should probably use
+ *      asm-generic/mutex-dec.h instead, or you could open-code an
+ *      optimized version in asm/mutex.h.
+ */
+#ifndef _ASM_GENERIC_MUTEX_XCHG_H
+#define _ASM_GENERIC_MUTEX_XCHG_H
+
+/**
+ *  __mutex_fastpath_lock - try to take the lock by moving the count
+ *                          from 1 to a 0 value
+ *  @count: pointer of type atomic_t
+ *  @fail_fn: function to call if the original value was not 1
+ *
+ * Change the count from 1 to a value lower than 1, and call <fail_fn> if it
+ * wasn't 1 originally. This function MUST leave the value lower than 1
+ * even when the "1" assertion wasn't true.
+ */
+static inline void
+__mutex_fastpath_lock(atomic_t *count, void (*fail_fn)(atomic_t *))
+{
+       if (unlikely(atomic_xchg(count, 0) != 1))
+               /*
+                * We failed to acquire the lock, so mark it contended
+                * to ensure that any waiting tasks are woken up by the
+                * unlock slow path.
+                */
+               if (likely(atomic_xchg(count, -1) != 1))
+                       fail_fn(count);
+}
+
+/**
+ *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
+ *                                 from 1 to a 0 value
+ *  @count: pointer of type atomic_t
+ *
+ * Change the count from 1 to a value lower than 1. This function returns 0
+ * if the fastpath succeeds, or -1 otherwise.
+ */
+static inline int
+__mutex_fastpath_lock_retval(atomic_t *count)
+{
+       if (unlikely(atomic_xchg(count, 0) != 1))
+               if (likely(atomic_xchg(count, -1) != 1))
+                       return -1;
+       return 0;
+}
+
+/**
+ *  __mutex_fastpath_unlock - try to promote the mutex from 0 to 1
+ *  @count: pointer of type atomic_t
+ *  @fail_fn: function to call if the original value was not 0
+ *
+ * try to promote the mutex from 0 to 1. if it wasn't 0, call <function>
+ * In the failure case, this function is allowed to either set the value to
+ * 1, or to set it to a value lower than one.
+ * If the implementation sets it to a value of lower than one, the
+ * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
+ * to return 0 otherwise.
+ */
+static inline void
+__mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
+{
+       if (unlikely(atomic_xchg(count, 1) != 0))
+               fail_fn(count);
+}
+
+#define __mutex_slowpath_needs_to_unlock()             0
+
+/**
+ * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
+ *
+ *  @count: pointer of type atomic_t
+ *  @fail_fn: spinlock based trylock implementation
+ *
+ * Change the count from 1 to a value lower than 1, and return 0 (failure)
+ * if it wasn't 1 originally, or return 1 (success) otherwise. This function
+ * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
+ * Additionally, if the value was < 0 originally, this function must not leave
+ * it to 0 on failure.
+ *
+ * If the architecture has no effective trylock variant, it should call the
+ * <fail_fn> spinlock-based trylock variant unconditionally.
+ */
+static inline int
+__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
+{
+       int prev = atomic_xchg(count, 0);
+
+       if (unlikely(prev < 0)) {
+               /*
+                * The lock was marked contended so we must restore that
+                * state. If while doing so we get back a prev value of 1
+                * then we just own it.
+                *
+                * [ In the rare case of the mutex going to 1, to 0, to -1
+                *   and then back to 0 in this few-instructions window,
+                *   this has the potential to trigger the slowpath for the
+                *   owner's unlock path needlessly, but that's not a problem
+                *   in practice. ]
+                */
+               prev = atomic_xchg(count, prev);
+               if (prev < 0)
+                       prev = 0;
+       }
+
+       return prev;
+}
+
+#endif