linux-kernel - Re: ftrace: preemptoff selftest not working

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Date:	Tue, 18 Nov 2008 12:21:19 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: ftrace: preemptoff selftest not working


On Tue, 18 Nov 2008, Heiko Carstens wrote:
> > 
> > we can drop it in selected initcalls just fine. Its only role is 
> > old-style init functions racing with other async contexts of 
> > themselves.
> 
> Something like below works fine for me...
> 
> Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>

Acked-by: Steven Rostedt <srostedt@...hat.com>

-- Steve

> ---
> 
>  kernel/trace/trace.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> Index: linux-2.6/kernel/trace/trace.c
> ===================================================================
> --- linux-2.6.orig/kernel/trace/trace.c
> +++ linux-2.6/kernel/trace/trace.c
> @@ -482,6 +482,13 @@ int register_tracer(struct tracer *type)
>  	}
>  
>  #ifdef CONFIG_FTRACE_STARTUP_TEST
> +	/*
> +	 * When this gets called we hold the BKL which means that preemption
> +	 * is disabled. Various trace selftests however need to disable
> +	 * and enable preemption for successful tests. So we drop the BKL here
> +	 * and grab it after the tests again.
> +	 */
> +	unlock_kernel();
>  	if (type->selftest) {
>  		struct tracer *saved_tracer = current_trace;
>  		struct trace_array *tr = &global_trace;
> @@ -515,6 +522,7 @@ int register_tracer(struct tracer *type)
>  		}
>  		printk(KERN_CONT "PASSED\n");
>  	}
> +	lock_kernel();
>  #endif
>  
>  	type->next = trace_types;
> 
> 
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