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

Paul E. McKenney
2011-06-08T19:40:24Z

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
>