Re: [for-next][PATCH 4/7] tracing: Rename trace_active to disable_stack_tracer and inline its modification

Valentin Rothberg
2017-04-13T07:58:34Z

Hi Steven,

I just found this patch in linux-next commit 8aaf1ee70e19 with
scripts/checkkconfigsymbols.py complaining about an undefined
CONFIG_PREEMPT_DEBUG (see below). I guess it's just a typo, since
there is a symbol named DEBUG_PREEMPT.

If you want to, I can send a trivial patch to rename both references.

Best regards,
Valentin

On Apr 10 '17 15:52, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
>
> In order to eliminate a function call, make "trace_active" into
> "disable_stack_tracer" and convert stack_tracer_disable() and friends into
> static inline functions.
>
> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
> include/linux/ftrace.h | 36 +++++++++++++++++++++++++++++++--
> kernel/trace/trace_stack.c | 50 +++++++++-------------------------------------
> 2 files changed, 43 insertions(+), 43 deletions(-)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 7b4e6572ab21..06b2990a35e4 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -287,8 +287,40 @@ stack_trace_sysctl(struct ctl_table *table, int write,
> void __user *buffer, size_t *lenp,
> loff_t *ppos);
>
> -void stack_tracer_disable(void);
> -void stack_tracer_enable(void);
> +/* DO NOT MODIFY THIS VARIABLE DIRECTLY! */
> +DECLARE_PER_CPU(int, disable_stack_tracer);
> +
> +/**
> + * stack_tracer_disable - temporarily disable the stack tracer
> + *
> + * There's a few locations (namely in RCU) where stack tracing
> + * cannot be executed. This function is used to disable stack
> + * tracing during those critical sections.
> + *
> + * This function must be called with preemption or interrupts
> + * disabled and stack_tracer_enable() must be called shortly after
> + * while preemption or interrupts are still disabled.
> + */
> +static inline void stack_tracer_disable(void)
> +{
> + /* Preemption or interupts must be disabled */
> + if (IS_ENABLED(CONFIG_PREEMPT_DEBUG))
^ undefined
> + WARN_ON_ONCE(!preempt_count() || !irqs_disabled());
> + this_cpu_inc(disable_stack_tracer);
> +}
> +
> +/**
> + * stack_tracer_enable - re-enable the stack tracer
> + *
> + * After stack_tracer_disable() is called, stack_tracer_enable()
> + * must be called shortly afterward.
> + */
> +static inline void stack_tracer_enable(void)
> +{
> + if (IS_ENABLED(CONFIG_PREEMPT_DEBUG))
^ undefined
> + WARN_ON_ONCE(!preempt_count() || !irqs_disabled());
> + this_cpu_dec(disable_stack_tracer);
> +}
> #else
> static inline void stack_tracer_disable(void) { }
> static inline void stack_tracer_enable(void) { }
> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index 21e536cf66e4..f2f02ff350d4 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -35,44 +35,12 @@ unsigned long stack_trace_max_size;
> arch_spinlock_t stack_trace_max_lock =
> (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
>
> -static DEFINE_PER_CPU(int, trace_active);
> +DEFINE_PER_CPU(int, disable_stack_tracer);
> static DEFINE_MUTEX(stack_sysctl_mutex);
>
> int stack_tracer_enabled;
> static int last_stack_tracer_enabled;
>
> -/**
> - * stack_tracer_disable - temporarily disable the stack tracer
> - *
> - * There's a few locations (namely in RCU) where stack tracing
> - * cannot be executed. This function is used to disable stack
> - * tracing during those critical sections.
> - *
> - * This function must be called with preemption or interrupts
> - * disabled and stack_tracer_enable() must be called shortly after
> - * while preemption or interrupts are still disabled.
> - */
> -void stack_tracer_disable(void)
> -{
> - /* Preemption or interupts must be disabled */
> - if (IS_ENABLED(CONFIG_PREEMPT_DEBUG))
> - WARN_ON_ONCE(!preempt_count() || !irqs_disabled());
> - this_cpu_inc(trace_active);
> -}
> -
> -/**
> - * stack_tracer_enable - re-enable the stack tracer
> - *
> - * After stack_tracer_disable() is called, stack_tracer_enable()
> - * must be called shortly afterward.
> - */
> -void stack_tracer_enable(void)
> -{
> - if (IS_ENABLED(CONFIG_PREEMPT_DEBUG))
> - WARN_ON_ONCE(!preempt_count() || !irqs_disabled());
> - this_cpu_dec(trace_active);
> -}
> -
> void stack_trace_print(void)
> {
> long i;
> @@ -243,8 +211,8 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip,
> preempt_disable_notrace();
>
> /* no atomic needed, we only modify this variable by this cpu */
> - __this_cpu_inc(trace_active);
> - if (__this_cpu_read(trace_active) != 1)
> + __this_cpu_inc(disable_stack_tracer);
> + if (__this_cpu_read(disable_stack_tracer) != 1)
> goto out;
>
> ip += MCOUNT_INSN_SIZE;
> @@ -252,7 +220,7 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip,
> check_stack(ip, &stack);
>
> out:
> - __this_cpu_dec(trace_active);
> + __this_cpu_dec(disable_stack_tracer);
> /* prevent recursion in schedule */
> preempt_enable_notrace();
> }
> @@ -294,15 +262,15 @@ stack_max_size_write(struct file *filp, const char __user *ubuf,
> /*
> * In case we trace inside arch_spin_lock() or after (NMI),
> * we will cause circular lock, so we also need to increase
> - * the percpu trace_active here.
> + * the percpu disable_stack_tracer here.
> */
> - __this_cpu_inc(trace_active);
> + __this_cpu_inc(disable_stack_tracer);
>
> arch_spin_lock(&stack_trace_max_lock);
> *ptr = val;
> arch_spin_unlock(&stack_trace_max_lock);
>
> - __this_cpu_dec(trace_active);
> + __this_cpu_dec(disable_stack_tracer);
> local_irq_restore(flags);
>
> return count;
> @@ -338,7 +306,7 @@ static void *t_start(struct seq_file *m, loff_t *pos)
> {
> local_irq_disable();
>
> - __this_cpu_inc(trace_active);
> + __this_cpu_inc(disable_stack_tracer);
>
> arch_spin_lock(&stack_trace_max_lock);
>
> @@ -352,7 +320,7 @@ static void t_stop(struct seq_file *m, void *p)
> {
> arch_spin_unlock(&stack_trace_max_lock);
>
> - __this_cpu_dec(trace_active);
> + __this_cpu_dec(disable_stack_tracer);
>
> local_irq_enable();
> }
> --
> 2.10.2
>
>