linux-kernel - [PATCH 4/5] RISC-V: Move to ticket-spinlocks

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Message-Id: <20220316232600.20419-5-palmer@rivosinc.com>
Date:   Wed, 16 Mar 2022 16:25:59 -0700
From:   Palmer Dabbelt <palmer@...osinc.com>
To:         linux-riscv@...ts.infradead.org, peterz@...radead.org
Cc:     jonas@...thpole.se, stefan.kristiansson@...nalahti.fi,
        shorne@...il.com, mingo@...hat.com, Will Deacon <will@...nel.org>,
        longman@...hat.com, boqun.feng@...il.com,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>, aou@...s.berkeley.edu,
        Arnd Bergmann <arnd@...db.de>, jszhang@...nel.org,
        wangkefeng.wang@...wei.com, openrisc@...ts.librecores.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-arch@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>
Subject: [PATCH 4/5] RISC-V: Move to ticket-spinlocks

From: Palmer Dabbelt <palmer@...osinc.com>

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.

Signed-off-by: Palmer Dabbelt <palmer@...osinc.com>
---
 arch/riscv/include/asm/Kbuild           |  2 ++
 arch/riscv/include/asm/spinlock.h       | 41 +------------------------
 arch/riscv/include/asm/spinlock_types.h |  6 +---
 3 files changed, 4 insertions(+), 45 deletions(-)

diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 57b86fd9916c..42b1961af1a6 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -2,5 +2,7 @@
 generic-y += early_ioremap.h
 generic-y += flat.h
 generic-y += kvm_para.h
+generic-y += ticket-lock.h
+generic-y += ticket-lock-types.h
 generic-y += user.h
 generic-y += vmlinux.lds.h
diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
index f4f7fa1b7ca8..38089cbdea92 100644
--- a/arch/riscv/include/asm/spinlock.h
+++ b/arch/riscv/include/asm/spinlock.h
@@ -10,46 +10,7 @@
 #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/ticket-lock.h>
 
 static inline void arch_read_lock(arch_rwlock_t *lock)
 {
diff --git a/arch/riscv/include/asm/spinlock_types.h b/arch/riscv/include/asm/spinlock_types.h
index 5a35a49505da..431ee08e26c4 100644
--- a/arch/riscv/include/asm/spinlock_types.h
+++ b/arch/riscv/include/asm/spinlock_types.h
@@ -10,11 +10,7 @@
 # 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/ticket-lock-types.h>
 
 typedef struct {
 	volatile unsigned int lock;
-- 
2.34.1