On Fri, May 31, 2013 at 09:30:18PM -0400, Steven Rostedt wrote:
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 65349f0..15c9f2e 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -71,6 +71,44 @@ void user_enter(void)
> local_irq_restore(flags);
> }
>
> +/**
> + * preempt_schedule_context - preempt_schedule called by tracing
> + *
> + * The tracing infrastructure uses preempt_enable_notrace to prevent
> + * recursion and tracing preempt enabling caused by the tracing
> + * infrastructure itself. But as tracing can happen in areas coming
> + * from userspace or just about to enter userspace, a preempt enable
> + * can occur before user_exit() is called. This will cause the scheduler
> + * to be called when the system is still in usermode.
> + *
> + * To prevent this, the preempt_enable_notrace will use this function
> + * instead of preempt_schedule() to exit user context if needed before
> + * calling the scheduler.
> + */
> +void __sched notrace preempt_schedule_context(void)
Should it be under CONFIG_PREEMPT?
> +{
> + struct thread_info *ti = current_thread_info();
> + enum ctx_state prev_ctx;
> +
> + if (likely(ti->preempt_count || irqs_disabled()))
> + return;
> +
> + /*
> + * Need to disable preemption in case user_exit() is traced
> + * and the tracer calls preempt_enable_notrace() causing
> + * an infinite recursion.
> + */
> + preempt_disable_notrace();
> + prev_ctx = exception_enter();
> + preempt_enable_no_resched_notrace();
> +
> + preempt_schedule();
> +
> + preempt_disable_notrace();
> + exception_exit(prev_ctx);
> + preempt_enable_notrace();
> +}
> +EXPORT_SYMBOL(preempt_schedule_context);
>
> /**
> * user_exit - Inform the context tracking that the CPU is
> --
> 1.7.3.4
>
>
>
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