linux-kernel - Re: [RFC PATCH 5/6] perf: Fix race in callchains

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Date:	Thu, 1 Jul 2010 17:42:36 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>,
	David Miller <davem@...emloft.net>,
	Borislav Petkov <bp@...64.org>
Subject: Re: [RFC PATCH 5/6] perf: Fix race in callchains

On Thu, Jul 01, 2010 at 05:36:01PM +0200, Frederic Weisbecker wrote:
> +static struct perf_callchain_entry *get_callchain_entry(int *rctx)
> +{
> +	struct perf_callchain_entry_cpus *cpu_entries;
> +
> +	*rctx = get_recursion_context(&__get_cpu_var(callchain_recursion));
> +	if (*rctx == -1)
> +		return NULL;
> +
> +	cpu_entries = rcu_dereference(callchain_entries[*rctx]);
> +	if (!cpu_entries)
> +		return NULL;
> +
> +	return this_cpu_ptr(cpu_entries->entries);
> +}
> +
> +static void
> +put_callchain_entry(int rctx)
> +{
> +	put_recursion_context(&__get_cpu_var(callchain_recursion), rctx);
> +}
> +
> +static struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
> +{
> +	int rctx;
> +	struct perf_callchain_entry *entry;
> +
> +
> +	entry = get_callchain_entry(&rctx);
> +	if (!entry)
> +		goto exit_put;


I realize this should only call put_callchain_entry() if rctx == -1, but you
got the idea...



> +
> +	entry->nr = 0;
> +
> +	if (!user_mode(regs)) {
> +		perf_callchain_store(entry, PERF_CONTEXT_KERNEL);
> +		perf_callchain_kernel(entry, regs);
> +		if (current->mm)
> +			regs = task_pt_regs(current);
> +		else
> +			regs = NULL;
> +	}
> +
> +	if (regs) {
> +		perf_callchain_store(entry, PERF_CONTEXT_USER);
> +		perf_callchain_user(entry, regs);
> +	}
> +
> +exit_put:
> +	put_callchain_entry(rctx);
> +
> +	return entry;
> +}

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