linux-kernel - Re: csky: smp_mb__after

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Date:   Wed, 5 Aug 2020 12:44:15 +0200
From:   peterz@...radead.org
To:     ren_guo@...ky.com
Cc:     linux-kernel@...r.kernel.org, linux-csky@...r.kernel.org,
        mathieu.desnoyers@...icios.com, Will Deacon <will@...nel.org>
Subject: Re: csky: smp_mb__after_spinlock

On Wed, Aug 05, 2020 at 12:41:46PM +0200, peterz@...radead.org wrote:
> Hi,
> 
> While doing an audit of smp_mb__after_spinlock, I found that csky
> defines it, why?
> 
> CSKY only has smp_mb(), it doesn't override __atomic_acquire_fence or
> otherwise special cases it's atomic*_acquire() primitives. It has an
> explicit smp_mb() in its arch_spin_lock().

Also, why have two implementations of all the locking ?

---
diff --git a/arch/csky/Kconfig b/arch/csky/Kconfig
index bd31ab12f77d..332738e93e57 100644
--- a/arch/csky/Kconfig
+++ b/arch/csky/Kconfig
@@ -7,7 +7,7 @@ config CSKY
 	select ARCH_HAS_SYNC_DMA_FOR_CPU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select ARCH_USE_BUILTIN_BSWAP
-	select ARCH_USE_QUEUED_RWLOCKS if NR_CPUS>2
+	select ARCH_USE_QUEUED_RWLOCKS
 	select ARCH_WANT_FRAME_POINTERS if !CPU_CK610
 	select COMMON_CLK
 	select CLKSRC_MMIO
diff --git a/arch/csky/include/asm/spinlock.h b/arch/csky/include/asm/spinlock.h
index 7cf3f2b34cea..69f5aa249c5f 100644
--- a/arch/csky/include/asm/spinlock.h
+++ b/arch/csky/include/asm/spinlock.h
@@ -6,8 +6,6 @@
 #include <linux/spinlock_types.h>
 #include <asm/barrier.h>
 
-#ifdef CONFIG_QUEUED_RWLOCKS
-
 /*
  * Ticket-based spin-locking.
  */
@@ -88,169 +86,4 @@ static inline int arch_spin_is_contended(arch_spinlock_t *lock)
 
 #include <asm/qrwlock.h>
 
-/* See include/linux/spinlock.h */
-#define smp_mb__after_spinlock()	smp_mb()
-
-#else /* CONFIG_QUEUED_RWLOCKS */
-
-/*
- * Test-and-set spin-locking.
- */
-static inline void arch_spin_lock(arch_spinlock_t *lock)
-{
-	u32 *p = &lock->lock;
-	u32 tmp;
-
-	asm volatile (
-		"1:	ldex.w		%0, (%1) \n"
-		"	bnez		%0, 1b   \n"
-		"	movi		%0, 1    \n"
-		"	stex.w		%0, (%1) \n"
-		"	bez		%0, 1b   \n"
-		: "=&r" (tmp)
-		: "r"(p)
-		: "cc");
-	smp_mb();
-}
-
-static inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
-	smp_mb();
-	WRITE_ONCE(lock->lock, 0);
-}
-
-static inline int arch_spin_trylock(arch_spinlock_t *lock)
-{
-	u32 *p = &lock->lock;
-	u32 tmp;
-
-	asm volatile (
-		"1:	ldex.w		%0, (%1) \n"
-		"	bnez		%0, 2f   \n"
-		"	movi		%0, 1    \n"
-		"	stex.w		%0, (%1) \n"
-		"	bez		%0, 1b   \n"
-		"	movi		%0, 0    \n"
-		"2:				 \n"
-		: "=&r" (tmp)
-		: "r"(p)
-		: "cc");
-
-	if (!tmp)
-		smp_mb();
-
-	return !tmp;
-}
-
-#define arch_spin_is_locked(x)	(READ_ONCE((x)->lock) != 0)
-
-/*
- * read lock/unlock/trylock
- */
-static inline void arch_read_lock(arch_rwlock_t *lock)
-{
-	u32 *p = &lock->lock;
-	u32 tmp;
-
-	asm volatile (
-		"1:	ldex.w		%0, (%1) \n"
-		"	blz		%0, 1b   \n"
-		"	addi		%0, 1    \n"
-		"	stex.w		%0, (%1) \n"
-		"	bez		%0, 1b   \n"
-		: "=&r" (tmp)
-		: "r"(p)
-		: "cc");
-	smp_mb();
-}
-
-static inline void arch_read_unlock(arch_rwlock_t *lock)
-{
-	u32 *p = &lock->lock;
-	u32 tmp;
-
-	smp_mb();
-	asm volatile (
-		"1:	ldex.w		%0, (%1) \n"
-		"	subi		%0, 1    \n"
-		"	stex.w		%0, (%1) \n"
-		"	bez		%0, 1b   \n"
-		: "=&r" (tmp)
-		: "r"(p)
-		: "cc");
-}
-
-static inline int arch_read_trylock(arch_rwlock_t *lock)
-{
-	u32 *p = &lock->lock;
-	u32 tmp;
-
-	asm volatile (
-		"1:	ldex.w		%0, (%1) \n"
-		"	blz		%0, 2f   \n"
-		"	addi		%0, 1    \n"
-		"	stex.w		%0, (%1) \n"
-		"	bez		%0, 1b   \n"
-		"	movi		%0, 0    \n"
-		"2:				 \n"
-		: "=&r" (tmp)
-		: "r"(p)
-		: "cc");
-
-	if (!tmp)
-		smp_mb();
-
-	return !tmp;
-}
-
-/*
- * write lock/unlock/trylock
- */
-static inline void arch_write_lock(arch_rwlock_t *lock)
-{
-	u32 *p = &lock->lock;
-	u32 tmp;
-
-	asm volatile (
-		"1:	ldex.w		%0, (%1) \n"
-		"	bnez		%0, 1b   \n"
-		"	subi		%0, 1    \n"
-		"	stex.w		%0, (%1) \n"
-		"	bez		%0, 1b   \n"
-		: "=&r" (tmp)
-		: "r"(p)
-		: "cc");
-	smp_mb();
-}
-
-static inline void arch_write_unlock(arch_rwlock_t *lock)
-{
-	smp_mb();
-	WRITE_ONCE(lock->lock, 0);
-}
-
-static inline int arch_write_trylock(arch_rwlock_t *lock)
-{
-	u32 *p = &lock->lock;
-	u32 tmp;
-
-	asm volatile (
-		"1:	ldex.w		%0, (%1) \n"
-		"	bnez		%0, 2f   \n"
-		"	subi		%0, 1    \n"
-		"	stex.w		%0, (%1) \n"
-		"	bez		%0, 1b   \n"
-		"	movi		%0, 0    \n"
-		"2:				 \n"
-		: "=&r" (tmp)
-		: "r"(p)
-		: "cc");
-
-	if (!tmp)
-		smp_mb();
-
-	return !tmp;
-}
-
-#endif /* CONFIG_QUEUED_RWLOCKS */
 #endif /* __ASM_CSKY_SPINLOCK_H */