s390: implement arch_xor_unlock_is_negative_byte

Inspired by the s390 arch_test_and_clear_bit(), this will surely be more
efficient than the generic one defined in filemap.c.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Cc: Albert Ou <[email protected]>
Cc: Alexander Gordeev <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Christian Borntraeger <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Matt Turner <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Paul Walmsley <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: "Theodore Ts'o" <[email protected]>
Cc: Thomas Bogendoerfer <[email protected]>
Cc: Vasily Gorbik <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Matthew Wilcox (Oracle)

arch/s390/include/asm/bitops.h

@@ -201,6 +201,16 @@ static inline void arch___clear_bit_unlock(unsigned long nr,
 	arch___clear_bit(nr, ptr);
 }
 
+static inline bool arch_xor_unlock_is_negative_byte(unsigned long mask,
+		volatile unsigned long *ptr)
+{
+	unsigned long old;
+
+	old = __atomic64_xor_barrier(mask, (long *)ptr);
+	return old & BIT(7);
+}
+#define arch_xor_unlock_is_negative_byte arch_xor_unlock_is_negative_byte
+
 #include <asm-generic/bitops/instrumented-atomic.h>
 #include <asm-generic/bitops/instrumented-non-atomic.h>
 #include <asm-generic/bitops/instrumented-lock.h>