bitops: add xor_unlock_is_negative_byte()

Replace clear_bit_and_unlock_is_negative_byte() with
xor_unlock_is_negative_byte().  We have a few places that like to lock a
folio, set a flag and unlock it again.  Allow for the possibility of
combining the latter two operations for efficiency.  We are guaranteed
that the caller holds the lock, so it is safe to unlock it with the xor. 
The caller must guarantee that nobody else will set the flag without
holding the lock; it is not safe to do this with the PG_dirty flag, for
example.

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]>

1 files changed, 5 insertions, 12 deletions

diff --git a/arch/powerpc/include/asm/bitops.h b/arch/powerpc/include/asm/bitops.h
index 7e0f0322912b..40cc3ded60cb 100644
--- a/arch/powerpc/include/asm/bitops.h
+++ b/arch/powerpc/include/asm/bitops.h
@@ -234,32 +234,25 @@ static inline int arch_test_and_change_bit(unsigned long nr,
 }
 
 #ifdef CONFIG_PPC64
-static inline unsigned long
-clear_bit_unlock_return_word(int nr, volatile unsigned long *addr)
+static inline bool arch_xor_unlock_is_negative_byte(unsigned long mask,
+		volatile unsigned long *p)
 {
 	unsigned long old, t;
-	unsigned long *p = (unsigned long *)addr + BIT_WORD(nr);
-	unsigned long mask = BIT_MASK(nr);
 
 	__asm__ __volatile__ (
 	PPC_RELEASE_BARRIER
 "1:"	PPC_LLARX "%0,0,%3,0\n"
-	"andc %1,%0,%2\n"
+	"xor %1,%0,%2\n"
 	PPC_STLCX "%1,0,%3\n"
 	"bne- 1b\n"
 	: "=&r" (old), "=&r" (t)
 	: "r" (mask), "r" (p)
 	: "cc", "memory");
 
-	return old;
+	return (old & BIT_MASK(7)) != 0;
 }
 
-/*
- * This is a special function for mm/filemap.c
- * Bit 7 corresponds to PG_waiters.
- */
-#define arch_clear_bit_unlock_is_negative_byte(nr, addr)		\
-	(clear_bit_unlock_return_word(nr, addr) & BIT_MASK(7))
+#define arch_xor_unlock_is_negative_byte arch_xor_unlock_is_negative_byte
 
 #endif /* CONFIG_PPC64 */