linux-kernel - Re: [PATCH] perf/x86/intel: Avoid unnecessary reallocations of memory allocated in cpu hotplug prepare state

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Date:   Tue, 18 Dec 2018 12:25:23 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     zhe.he@...driver.com, acme@...nel.org, ak@...ux.intel.com,
        alexander.shishkin@...ux.intel.com, bp@...en8.de, hpa@...or.com,
        jolsa@...nel.org, jolsa@...hat.com, kan.liang@...ux.intel.com,
        mingo@...hat.com, namhyung@...nel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH] perf/x86/intel: Avoid unnecessary reallocations of memory
 allocated in cpu hotplug prepare state

On Tue, 18 Dec 2018, Peter Zijlstra wrote:
> On Tue, Dec 18, 2018 at 06:30:33PM +0800, zhe.he@...driver.com wrote:
> > Besides, in preempt-rt full mode, the freeing can happen in atomic context and
> > thus cause the following BUG.
> 
> Hurm, I though we fixed all those long ago..

Either we missed that one or it came back somehow.

> And no, the patch is horrible; that's what we have things like
> x86_pmu::cpu_dead() for.

Like the below?

Thanks,

	tglx

8<------------

--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3559,6 +3559,14 @@ static void free_excl_cntrs(int cpu)
 
 static void intel_pmu_cpu_dying(int cpu)
 {
+	fini_debug_store_on_cpu(cpu);
+
+	if (x86_pmu.counter_freezing)
+		disable_counter_freeze();
+}
+
+static void intel_pmu_cpu_dead(int cpu)
+{
 	struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);
 	struct intel_shared_regs *pc;
 
@@ -3570,11 +3578,6 @@ static void intel_pmu_cpu_dying(int cpu)
 	}
 
 	free_excl_cntrs(cpu);
-
-	fini_debug_store_on_cpu(cpu);
-
-	if (x86_pmu.counter_freezing)
-		disable_counter_freeze();
 }
 
 static void intel_pmu_sched_task(struct perf_event_context *ctx,
@@ -3663,6 +3666,7 @@ static __initconst const struct x86_pmu
 	.cpu_prepare		= intel_pmu_cpu_prepare,
 	.cpu_starting		= intel_pmu_cpu_starting,
 	.cpu_dying		= intel_pmu_cpu_dying,
+	.cpu_dead		= intel_pmu_cpu_dead,
 };
 
 static struct attribute *intel_pmu_attrs[];
@@ -3703,6 +3707,7 @@ static __initconst const struct x86_pmu
 	.cpu_prepare		= intel_pmu_cpu_prepare,
 	.cpu_starting		= intel_pmu_cpu_starting,
 	.cpu_dying		= intel_pmu_cpu_dying,
+	.cpu_dead		= intel_pmu_cpu_dead,
 	.guest_get_msrs		= intel_guest_get_msrs,
 	.sched_task		= intel_pmu_sched_task,
 };