Re: [PATCH 2/4] sched: Isolate preempt counting in its own config option

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Wed, Jun 08, 2011 at 07:48:33PM +0200, Frederic Weisbecker wrote:
> Create a new CONFIG_PREEMPT_COUNT that handles the inc/dec
> of preempt count offset independently. So that the offset
> can be updated by preempt_disable() and preempt_enable()
> even without the need for CONFIG_PREEMPT beeing set.
> 
> This prepares to make CONFIG_DEBUG_SPINLOCK_SLEEP working
> with !CONFIG_PREEMPT where it currently doesn't detect
> code that sleeps inside explicit preemption disabled
> sections.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
>  include/linux/bit_spinlock.h |    2 +-
>  include/linux/hardirq.h      |    4 ++--
>  include/linux/pagemap.h      |    4 ++--
>  include/linux/preempt.h      |   26 +++++++++++++++++---------
>  include/linux/rcupdate.h     |   12 ++++++------
>  include/linux/sched.h        |    2 +-
>  kernel/Kconfig.preempt       |    3 +++
>  kernel/sched.c               |    2 +-
>  8 files changed, 33 insertions(+), 22 deletions(-)
> 
> diff --git a/include/linux/bit_spinlock.h b/include/linux/bit_spinlock.h
> index b4326bf..564d997 100644
> --- a/include/linux/bit_spinlock.h
> +++ b/include/linux/bit_spinlock.h
> @@ -88,7 +88,7 @@ static inline int bit_spin_is_locked(int bitnum, unsigned long *addr)
>  {
>  #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
>  	return test_bit(bitnum, addr);
> -#elif defined CONFIG_PREEMPT
> +#elif defined CONFIG_PREEMPT_COUNT
>  	return preempt_count();
>  #else
>  	return 1;
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index ba36217..f743883f 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -93,7 +93,7 @@
>   */
>  #define in_nmi()	(preempt_count() & NMI_MASK)
> 
> -#if defined(CONFIG_PREEMPT)
> +#if defined(CONFIG_PREEMPT_COUNT)
>  # define PREEMPT_CHECK_OFFSET 1
>  #else
>  # define PREEMPT_CHECK_OFFSET 0
> @@ -115,7 +115,7 @@
>  #define in_atomic_preempt_off() \
>  		((preempt_count() & ~PREEMPT_ACTIVE) != PREEMPT_CHECK_OFFSET)
> 
> -#ifdef CONFIG_PREEMPT
> +#ifdef CONFIG_PREEMPT_COUNT
>  # define preemptible()	(preempt_count() == 0 && !irqs_disabled())
>  # define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
>  #else
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 716875e..8e38d4c 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -134,7 +134,7 @@ static inline int page_cache_get_speculative(struct page *page)
>  	VM_BUG_ON(in_interrupt());
> 
>  #if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
> -# ifdef CONFIG_PREEMPT
> +# ifdef CONFIG_PREEMPT_COUNT
>  	VM_BUG_ON(!in_atomic());
>  # endif
>  	/*
> @@ -172,7 +172,7 @@ static inline int page_cache_add_speculative(struct page *page, int count)
>  	VM_BUG_ON(in_interrupt());
> 
>  #if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
> -# ifdef CONFIG_PREEMPT
> +# ifdef CONFIG_PREEMPT_COUNT
>  	VM_BUG_ON(!in_atomic());
>  # endif
>  	VM_BUG_ON(page_count(page) == 0);
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 2e681d9..58969b2 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -27,6 +27,21 @@
> 
>  asmlinkage void preempt_schedule(void);
> 
> +#define preempt_check_resched() \
> +do { \
> +	if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
> +		preempt_schedule(); \
> +} while (0)
> +
> +#else /* !CONFIG_PREEMPT */
> +
> +#define preempt_check_resched()		do { } while (0)
> +
> +#endif /* CONFIG_PREEMPT */
> +
> +
> +#ifdef CONFIG_PREEMPT_COUNT
> +
>  #define preempt_disable() \
>  do { \
>  	inc_preempt_count(); \
> @@ -39,12 +54,6 @@ do { \
>  	dec_preempt_count(); \
>  } while (0)
> 
> -#define preempt_check_resched() \
> -do { \
> -	if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \
> -		preempt_schedule(); \
> -} while (0)
> -
>  #define preempt_enable() \
>  do { \
>  	preempt_enable_no_resched(); \
> @@ -80,18 +89,17 @@ do { \
>  	preempt_check_resched(); \
>  } while (0)
> 
> -#else
> +#else /* !CONFIG_PREEMPT_COUNT */
> 
>  #define preempt_disable()		do { } while (0)
>  #define preempt_enable_no_resched()	do { } while (0)
>  #define preempt_enable()		do { } while (0)
> -#define preempt_check_resched()		do { } while (0)
> 
>  #define preempt_disable_notrace()		do { } while (0)
>  #define preempt_enable_no_resched_notrace()	do { } while (0)
>  #define preempt_enable_notrace()		do { } while (0)
> 
> -#endif
> +#endif /* CONFIG_PREEMPT_COUNT */
> 
>  #ifdef CONFIG_PREEMPT_NOTIFIERS
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 99f9aa7..8f4f881 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -239,7 +239,7 @@ extern int rcu_read_lock_bh_held(void);
>   * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
>   * and while lockdep is disabled.
>   */
> -#ifdef CONFIG_PREEMPT
> +#ifdef CONFIG_PREEMPT_COUNT
>  static inline int rcu_read_lock_sched_held(void)
>  {
>  	int lockdep_opinion = 0;
> @@ -250,12 +250,12 @@ static inline int rcu_read_lock_sched_held(void)
>  		lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
>  	return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
>  }
> -#else /* #ifdef CONFIG_PREEMPT */
> +#else /* #ifdef CONFIG_PREEMPT_COUNT */
>  static inline int rcu_read_lock_sched_held(void)
>  {
>  	return 1;
>  }
> -#endif /* #else #ifdef CONFIG_PREEMPT */
> +#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
> 
>  #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
> 
> @@ -276,17 +276,17 @@ static inline int rcu_read_lock_bh_held(void)
>  	return 1;
>  }
> 
> -#ifdef CONFIG_PREEMPT
> +#ifdef CONFIG_PREEMPT_COUNT
>  static inline int rcu_read_lock_sched_held(void)
>  {
>  	return preempt_count() != 0 || irqs_disabled();
>  }
> -#else /* #ifdef CONFIG_PREEMPT */
> +#else /* #ifdef CONFIG_PREEMPT_COUNT */
>  static inline int rcu_read_lock_sched_held(void)
>  {
>  	return 1;
>  }
> -#endif /* #else #ifdef CONFIG_PREEMPT */
> +#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
> 
>  #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 483c1ed..4ecd5cb 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2502,7 +2502,7 @@ extern int _cond_resched(void);
> 
>  extern int __cond_resched_lock(spinlock_t *lock);
> 
> -#ifdef CONFIG_PREEMPT
> +#ifdef CONFIG_PREEMPT_COUNT
>  #define PREEMPT_LOCK_OFFSET	PREEMPT_OFFSET
>  #else
>  #define PREEMPT_LOCK_OFFSET	0
> diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
> index bf987b9..24e7cb0 100644
> --- a/kernel/Kconfig.preempt
> +++ b/kernel/Kconfig.preempt
> @@ -35,6 +35,7 @@ config PREEMPT_VOLUNTARY
> 
>  config PREEMPT
>  	bool "Preemptible Kernel (Low-Latency Desktop)"
> +	select PREEMPT_COUNT
>  	help
>  	  This option reduces the latency of the kernel by making
>  	  all kernel code (that is not executing in a critical section)
> @@ -52,3 +53,5 @@ config PREEMPT
> 
>  endchoice
> 
> +config PREEMPT_COUNT
> +       bool
> \ No newline at end of file
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 01d9536..90ad7cf 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -2843,7 +2843,7 @@ void sched_fork(struct task_struct *p)
>  #if defined(CONFIG_SMP)
>  	p->on_cpu = 0;
>  #endif
> -#ifdef CONFIG_PREEMPT
> +#ifdef CONFIG_PREEMPT_COUNT
>  	/* Want to start with kernel preemption disabled. */
>  	task_thread_info(p)->preempt_count = 1;
>  #endif
> -- 
> 1.7.5.4
>