[PATCH v9 2/5] qrwlock x86: Enable x86 to use queue read/write lock

[Waiman Long <Waiman.Long@hp.com>]

This patch makes the necessary changes at the x86 architecture specific
layer to enable the presence of the CONFIG_QUEUE_RWLOCK kernel option
to replace the read/write lock by the queue read/write lock.

It also enables the CONFIG_QUEUE_RWLOCK option by default for x86 which
will force the use of queue read/write lock. That will greatly improve
the fairness of read/write lock and eliminate live-lock situation
where one task may not get the lock for an indefinite period of time.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 arch/x86/Kconfig                      |    1 +
 arch/x86/include/asm/spinlock.h       |    2 ++
 arch/x86/include/asm/spinlock_types.h |    4 ++++
 3 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e0acf82..3c6094b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -119,6 +119,7 @@ config X86
 	select MODULES_USE_ELF_RELA if X86_64
 	select CLONE_BACKWARDS if X86_32
 	select ARCH_USE_BUILTIN_BSWAP
+	select ARCH_USE_QUEUE_RWLOCK
 	select OLD_SIGSUSPEND3 if X86_32 || IA32_EMULATION
 	select OLD_SIGACTION if X86_32
 	select COMPAT_OLD_SIGACTION if IA32_EMULATION
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index bf156de..8fb88c5 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -188,6 +188,7 @@ static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
 		cpu_relax();
 }
 
+#ifndef CONFIG_QUEUE_RWLOCK
 /*
  * Read-write spinlocks, allowing multiple readers
  * but only one writer.
@@ -270,6 +271,7 @@ static inline void arch_write_unlock(arch_rwlock_t *rw)
 	asm volatile(LOCK_PREFIX WRITE_LOCK_ADD(%1) "%0"
 		     : "+m" (rw->write) : "i" (RW_LOCK_BIAS) : "memory");
 }
+#endif /* CONFIG_QUEUE_RWLOCK */
 
 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
index 4f1bea1..a585635 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -34,6 +34,10 @@ typedef struct arch_spinlock {
 
 #define __ARCH_SPIN_LOCK_UNLOCKED	{ { 0 } }
 
+#ifdef CONFIG_QUEUE_RWLOCK
+#include <asm-generic/qrwlock.h>
+#else
 #include <asm/rwlock.h>
+#endif
 
 #endif /* _ASM_X86_SPINLOCK_TYPES_H */
-- 
1.7.1