On Fri, Nov 22, 2013 at 02:04:45PM -0500, Waiman Long wrote:
> 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@xxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> ---
> 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 e903c71..c4a9c54 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -124,6 +124,7 @@ config X86
> select RTC_LIB
> select HAVE_DEBUG_STACKOVERFLOW
> select HAVE_IRQ_EXIT_ON_IRQ_STACK if X86_64
> + select QUEUE_RWLOCK
>
> config INSTRUCTION_DECODER
> def_bool y
> 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
>
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