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authorPeter Zijlstra <peterz@infradead.org>2016-06-01 20:23:54 +0300
committerIngo Molnar <mingo@kernel.org>2016-06-14 12:55:14 +0300
commit7cb45c0fe9858f92cc264f6bf9d2f6a0e7d3b249 (patch)
treef429581d6b993e303a297a461d06cd0dad58ea68 /include/asm-generic
parent33ac279677dcc2441cb93d8cb9cf7a74df62814d (diff)
downloadlinux-7cb45c0fe9858f92cc264f6bf9d2f6a0e7d3b249.tar.xz
locking/barriers: Move smp_cond_load_acquire() to asm-generic/barrier.h
Since all asm/barrier.h should/must include asm-generic/barrier.h the latter is a good place for generic infrastructure like this. This also allows archs to override the new smp_acquire__after_ctrl_dep(). Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/asm-generic')
-rw-r--r--include/asm-generic/barrier.h39
1 files changed, 39 insertions, 0 deletions
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 1cceca146905..ab7b0bd7d4dd 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -207,5 +207,44 @@ do { \
#define virt_store_release(p, v) __smp_store_release(p, v)
#define virt_load_acquire(p) __smp_load_acquire(p)
+/**
+ * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency
+ *
+ * A control dependency provides a LOAD->STORE order, the additional RMB
+ * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
+ * aka. (load)-ACQUIRE.
+ *
+ * Architectures that do not do load speculation can have this be barrier().
+ */
+#ifndef smp_acquire__after_ctrl_dep
+#define smp_acquire__after_ctrl_dep() smp_rmb()
+#endif
+
+/**
+ * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering
+ * @ptr: pointer to the variable to wait on
+ * @cond: boolean expression to wait for
+ *
+ * Equivalent to using smp_load_acquire() on the condition variable but employs
+ * the control dependency of the wait to reduce the barrier on many platforms.
+ *
+ * Due to C lacking lambda expressions we load the value of *ptr into a
+ * pre-named variable @VAL to be used in @cond.
+ */
+#ifndef smp_cond_load_acquire
+#define smp_cond_load_acquire(ptr, cond_expr) ({ \
+ typeof(ptr) __PTR = (ptr); \
+ typeof(*ptr) VAL; \
+ for (;;) { \
+ VAL = READ_ONCE(*__PTR); \
+ if (cond_expr) \
+ break; \
+ cpu_relax(); \
+ } \
+ smp_acquire__after_ctrl_dep(); \
+ VAL; \
+})
+#endif
+
#endif /* !__ASSEMBLY__ */
#endif /* __ASM_GENERIC_BARRIER_H */