linux-kernel - Re: [PATCH] pstore/ftrace: Convert to its own enable/disable debugfs knob

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Message-ID: <20120718072608.GA17026@lizard>
Date:	Wed, 18 Jul 2012 00:26:08 -0700
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Kees Cook <keescook@...omium.org>,
	Colin Cross <ccross@...roid.com>,
	Tony Luck <tony.luck@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Shuah Khan <shuahkhan@...il.com>, arve@...roid.com,
	Rebecca Schultz Zavin <rebecca@...roid.com>,
	Jesper Juhl <jj@...osbits.net>,
	Randy Dunlap <rdunlap@...otime.net>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Thomas Meyer <thomas@...3r.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marco Stornelli <marco.stornelli@...il.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	kernel-team@...roid.com
Subject: Re: [PATCH] pstore/ftrace: Convert to its own enable/disable debugfs
 knob

On Tue, Jul 17, 2012 at 08:47:22PM -0700, Anton Vorontsov wrote:
[...]
> -void notrace pstore_ftrace_call(unsigned long ip, unsigned long parent_ip)
> +static void notrace pstore_ftrace_call(unsigned long ip,
> +				       unsigned long parent_ip)
>  {
> +	unsigned long flags;
>  	struct pstore_ftrace_record rec = {};
>  
> +	if (unlikely(!ftrace_enabled))
> +		return;
>  	if (unlikely(oops_in_progress))
>  		return;
>  
> +	local_irq_save(flags);
> +
>  	rec.ip = ip;
>  	rec.parent_ip = parent_ip;
>  	pstore_ftrace_encode_cpu(&rec, raw_smp_processor_id());
>  	psinfo->write_buf(PSTORE_TYPE_FTRACE, 0, NULL, 0, (void *)&rec,
>  			  sizeof(rec), psinfo);

Btw, here we might be running w/o recurse protection, and that helped
to find a bug in the persistent ram module.

The bug was quite subtle: it only happened if pstore tracing was
enabled before any other tracers. And it magically disappeared
otherwise.

This is because ftrace_ops_list_func() does its own recurse protection,
but ftrace_ops_list_func() is only used when there are more than
one 'struct ops' registered, otherwise ->func is called directly.

Of course, if I specify FL_GLOBAL/FL_CONTROL flag for the tracer,
then it will not try to call the func directly. But then there is
a question: do we really want to set these flags if we yet don't
want removable modules?

Or, setting at least FL_CONTROL would be a good idea anyway, since
it will then react to ftrace_function_local_{enable,disable}()?

Thanks,

-- 
Anton Vorontsov
Email: cbouatmailru@...il.com
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