linux-kernel - Re: [PATCH 5/9] perf/x86: implement cross-HT corruption bug workaround

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Message-ID: <20140605134841.GL3213@twins.programming.kicks-ass.net>
Date:	Thu, 5 Jun 2014 15:48:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, ak@...ux.intel.com,
	jolsa@...hat.com, zheng.z.yan@...el.com,
	maria.n.dimakopoulou@...il.com
Subject: Re: [PATCH 5/9] perf/x86: implement cross-HT corruption bug
 workaround

On Wed, Jun 04, 2014 at 11:34:14PM +0200, Stephane Eranian wrote:

> +static struct event_constraint *
> +intel_get_excl_constraints(struct cpu_hw_events *cpuc, struct perf_event *event,
> +			   struct event_constraint *c)
> +{

> +	if (!(c->flags & PERF_X86_EVENT_DYNAMIC)) {
> +
> +		/*
> +		 * in case we fail, we assume no counter
> +		 * is supported to be on the safe side
> +		 */
> +		cx = kmalloc(sizeof(*cx), GFP_KERNEL);
> +		if (!cx)
> +			return &emptyconstraint;
> +

Ok, so forgive me if I'm wrong, but the way we get here is through:

x86_schedule_event()
  ->start_scheduling()
    spin_lock()
  ->get_event_constraints()
    intel_get_excl_constraints()
      kmalloc(.gfp=GFP_KERNEL)

How can that ever work?

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