arch: Prepare for smp_mb__{before,after}_atomic()

Since the smp_mb__{before,after}*() ops are fundamentally dependent on
how an arch can implement atomics it doesn't make sense to have 3
variants of them. They must all be the same.

Furthermore, the 3 variants suggest they're only valid for those 3
atomic ops, while we have many more where they could be applied.

So move away from
smp_mb__{before,after}_{atomic,clear}_{dec,inc,bit}() and reduce the
interface to just the two: smp_mb__{before,after}_atomic().

This patch prepares the way by introducing default implementations in
asm-generic/barrier.h that default to a full barrier and providing
__deprecated inlines for the previous 6 barriers if they're not
provided by the arch.

This should allow for a mostly painless transition (lots of deprecated
warns in the interim).

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/n/tip-wr59327qdyi9mbzn6x937s4e@git.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Chen, Gong" <gong.chen@linux.intel.com>
Cc: John Sullivan <jsrhbz@kanargh.force9.co.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mauro Carvalho Chehab <m.chehab@samsung.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: linux-arch@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index be5fd38bd5a0..cbc5833fb221 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -32,6 +32,26 @@ extern unsigned long __sw_hweight64(__u64 w);
  */
 #include <asm/bitops.h>
 
+/*
+ * Provide __deprecated wrappers for the new interface, avoid flag day changes.
+ * We need the ugly external functions to break header recursion hell.
+ */
+#ifndef smp_mb__before_clear_bit
+static inline void __deprecated smp_mb__before_clear_bit(void)
+{
+	extern void __smp_mb__before_atomic(void);
+	__smp_mb__before_atomic();
+}
+#endif
+
+#ifndef smp_mb__after_clear_bit
+static inline void __deprecated smp_mb__after_clear_bit(void)
+{
+	extern void __smp_mb__after_atomic(void);
+	__smp_mb__after_atomic();
+}
+#endif
+
 #define for_each_set_bit(bit, addr, size) \
 	for ((bit) = find_first_bit((addr), (size));		\
 	     (bit) < (size);					\