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Date: Wed, 25 Mar 2009 11:07:46 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Peter Zijlstra <peterz@infradead.org>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Tim Bird <tim.bird@am.sony.com>, Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 2/5][RFC] tracing: move function profiler data out of
	function struct
Message-ID: <20090325100746.GI2341@elte.hu>
References: <20090325035646.662994901@goodmis.org> <20090325040832.443420395@goodmis.org>
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* Steven Rostedt <rostedt@goodmis.org> wrote:

> +/* Interrupts must be disabled calling this */
> +static struct ftrace_profile *
> +ftrace_profile_alloc(unsigned long ip, bool alloc_safe)
> +{
> +	struct ftrace_profile *rec = NULL;
> +
> +	/* prevent recursion */
> +	if (atomic_inc_return(&__get_cpu_var(ftrace_profile_disable)) != 1)
> +		goto out;
> +
> +	__raw_spin_lock(&ftrace_profile_rec_lock);
> +
> +	/* Try to always keep another page available */
> +	if (!profile_pages->next && alloc_safe)
> +		profile_pages->next = (void *)get_zeroed_page(GFP_ATOMIC);

this does not seem to be NMI safe.

This all would be solved much more robustly by the function 
attributes hash approach i suggested in the previous mail. If 
percpu_alloc() is done for 20,000 functions the memory allocation 
overhead is no big deal.

	Ingo