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

[Frederic Weisbecker <fweisbec@gmail.com>]

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;
> +}