RISC-V: Move to generic spinlocks

Our existing spinlocks aren't fair and replacing them has been on the
TODO list for a long time.  This moves to the recently-introduced ticket
spinlocks, which are simple enough that they are likely to be correct
and fast on the vast majority of extant implementations.

This introduces a horrible hack that allows us to split out the spinlock
conversion from the rwlock conversion.  We have to do the spinlocks
first because qrwlock needs fair spinlocks, but we don't want to pollute
the asm-generic code to support the generic spinlocks without qrwlocks.
Thus we pollute the RISC-V code, but just until the next commit as it's
all going away.

Reviewed-by: Arnd Bergmann <[email protected]>
Reviewed-by: Guo Ren <[email protected]>
Tested-by: Heiko Stuebner <[email protected]>
Tested-by: Conor Dooley <[email protected]>
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: palmer-dabbelt

arch/riscv/include/asm/Kbuild

@@ -3,5 +3,7 @@ generic-y += early_ioremap.h
 generic-y += flat.h
 generic-y += kvm_para.h
 generic-y += parport.h
+generic-y += qrwlock.h
+generic-y += qrwlock_types.h
 generic-y += user.h
 generic-y += vmlinux.lds.h

arch/riscv/include/asm/spinlock.h

@@ -7,49 +7,13 @@
 #ifndef _ASM_RISCV_SPINLOCK_H
 #define _ASM_RISCV_SPINLOCK_H
 
+/* This is horible, but the whole file is going away in the next commit. */
+#define __ASM_GENERIC_QRWLOCK_H
+
 #include <linux/kernel.h>
 #include <asm/current.h>
 #include <asm/fence.h>
-
-/*
- * Simple spin lock operations.  These provide no fairness guarantees.
- */
-
-/* FIXME: Replace this with a ticket lock, like MIPS. */
-
-#define arch_spin_is_locked(x)	(READ_ONCE((x)->lock) != 0)
-
-static inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
-	smp_store_release(&lock->lock, 0);
-}
-
-static inline int arch_spin_trylock(arch_spinlock_t *lock)
-{
-	int tmp = 1, busy;
-
-	__asm__ __volatile__ (
-		"	amoswap.w %0, %2, %1\n"
-		RISCV_ACQUIRE_BARRIER
-		: "=r" (busy), "+A" (lock->lock)
-		: "r" (tmp)
-		: "memory");
-
-	return !busy;
-}
-
-static inline void arch_spin_lock(arch_spinlock_t *lock)
-{
-	while (1) {
-		if (arch_spin_is_locked(lock))
-			continue;
-
-		if (arch_spin_trylock(lock))
-			break;
-	}
-}
-
-/***********************************************************/
+#include <asm-generic/spinlock.h>
 
 static inline void arch_read_lock(arch_rwlock_t *lock)
 {

arch/riscv/include/asm/spinlock_types.h

@@ -6,15 +6,14 @@
 #ifndef _ASM_RISCV_SPINLOCK_TYPES_H
 #define _ASM_RISCV_SPINLOCK_TYPES_H
 
+/* This is horible, but the whole file is going away in the next commit. */
+#define __ASM_GENERIC_QRWLOCK_TYPES_H
+
 #ifndef __LINUX_SPINLOCK_TYPES_RAW_H
 # error "please don't include this file directly"
 #endif
 
-typedef struct {
-	volatile unsigned int lock;
-} arch_spinlock_t;
-
-#define __ARCH_SPIN_LOCK_UNLOCKED	{ 0 }
+#include <asm-generic/spinlock_types.h>
 
 typedef struct {
 	volatile unsigned int lock;