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SubjectRe: [PATCH 4/7] add syscall tracepoints
>  /*
> * A syscall entry in the ftrace syscalls array.
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 1ef5d3a..5b34ff9 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -24,6 +24,7 @@
> #include <linux/tracepoint.h>
> #include <linux/err.h>
> #include <linux/slab.h>
> +#include <linux/sched.h>
>
> extern struct tracepoint __start___tracepoints[];
> extern struct tracepoint __stop___tracepoints[];
> @@ -577,3 +578,40 @@ static int init_tracepoints(void)
> __initcall(init_tracepoints);
>
> #endif /* CONFIG_MODULES */
> +
> +DEFINE_MUTEX(regfunc_mutex);

static?

> +int sys_tracepoint_refcount;

static?

and atomic_t should be fine as Frederic pointed out.

> +
> +void syscall_regfunc(void)
> +{
> + unsigned long flags;
> + struct task_struct *g, *t;
> +
> + mutex_lock(&regfunc_mutex);
> + if (!sys_tracepoint_refcount) {
> + read_lock_irqsave(&tasklist_lock, flags);
> + do_each_thread(g, t) {
> + set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
> + } while_each_thread(g, t);
> + read_unlock_irqrestore(&tasklist_lock, flags);
> + }
> + sys_tracepoint_refcount++;
> + mutex_unlock(&regfunc_mutex);
> +}
> +
> +void syscall_unregfunc(void)
> +{
> + unsigned long flags;
> + struct task_struct *g, *t;
> +
> + mutex_lock(&regfunc_mutex);
> + sys_tracepoint_refcount--;
> + if (!sys_tracepoint_refcount) {
> + read_lock_irqsave(&tasklist_lock, flags);
> + do_each_thread(g, t) {
> + clear_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
> + } while_each_thread(g, t);
> + read_unlock_irqrestore(&tasklist_lock, flags);
> + }
> + mutex_unlock(&regfunc_mutex);
> +}



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