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Date: Thu, 29 Jan 2015 12:59:18 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
Robert Richter <rric@...nel.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Mike Galbraith <efault@....de>,
Paul Mackerras <paulus@...ba.org>,
Stephane Eranian <eranian@...gle.com>,
Andi Kleen <ak@...ux.intel.com>, kan.liang@...el.com,
adrian.hunter@...el.com, markus.t.metzger@...el.com,
mathieu.poirier@...aro.org, Kaixu Xia <kaixu.xia@...aro.org>,
acme@...radead.org
Subject: Re: [PATCH v9 12/14] x86: perf: intel_pt: Intel PT PMU driver
On Tue, Jan 27, 2015 at 08:03:47PM +0200, Alexander Shishkin wrote:
> +static int account_per_task_counter(struct perf_event *event)
> +{
> + struct pmu *pmu = event->pmu;
> +
> + if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
> + return 0;
> +
> + /*
> + * Prevent co-existence of per-task and cpu-wide events on the
> + * same exclusive pmu.
> + *
> + * Negative pmu::nr_per_task_events means there are cpu-wide
> + * events on this "exclusive" pmu, positive means there are
> + * per-task events.
> + */
> + if (event->cpu == -1 &&
> + !atomic_inc_unless_negative(&pmu->nr_per_task_events))
> + return -EBUSY;
> + else if (!(event->attach_state & PERF_ATTACH_TASK) &&
> + !atomic_dec_unless_positive(&pmu->nr_per_task_events))
> + return -EBUSY;
> +
> + return 0;
> +}
I think that logic fails for per-task events that have a cpu set.
> +static bool exclusive_event_ok(struct perf_event *event,
> + struct perf_event_context *ctx)
> +{
> + struct pmu *pmu = event->pmu;
> + bool ret = true;
> +
> + if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
> + return true;
> +
> + if (!__exclusive_event_ok(event, ctx))
> + return false;
> +
> + if (ctx->task) {
> + if (event->cpu != -1) {
> + struct perf_event_context *cpuctx;
> +
> + cpuctx = &per_cpu_ptr(pmu->pmu_cpu_context, event->cpu)->ctx;
> +
> + mutex_lock(&cpuctx->mutex);
> + ret = __exclusive_event_ok(event, cpuctx);
> + mutex_unlock(&cpuctx->mutex);
We're already holding ctx->mutex, this should have made lockdep scream.
> + }
> + }
> +
> + return ret;
> +}
Would something like this work?
---
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -168,6 +168,7 @@ struct perf_event;
#define PERF_PMU_CAP_NO_INTERRUPT 0x01
#define PERF_PMU_CAP_AUX_NO_SG 0x02
#define PERF_PMU_CAP_AUX_SW_DOUBLEBUF 0x04
+#define PERF_PMU_CAP_EXCLUSIVE 0x08
/**
* struct pmu - generic performance monitoring unit
@@ -188,6 +189,7 @@ struct pmu {
int * __percpu pmu_disable_count;
struct perf_cpu_context * __percpu pmu_cpu_context;
+ atomic_t exclusive_cnt; /* <0: cpu, >0: tsk */
int task_ctx_nr;
int hrtimer_interval_ms;
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3487,6 +3487,9 @@ static void __free_event(struct perf_eve
if (event->destroy)
event->destroy(event);
+ if (event->pmu && event->ctx)
+ exclusive_event_release(event);
+
if (event->ctx)
put_ctx(event->ctx);
@@ -7092,6 +7095,7 @@ int perf_pmu_register(struct pmu *pmu, c
pmu->event_idx = perf_event_idx_default;
list_add_rcu(&pmu->entry, &pmus);
+ atomic_set(&pmu->exclusive_cnt, 0);
ret = 0;
unlock:
mutex_unlock(&pmus_lock);
@@ -7537,6 +7541,78 @@ perf_event_set_output(struct perf_event
return ret;
}
+static bool exclusive_event_match(struct perf_event *e1, struct perf_event *e2)
+{
+ if ((e1->pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE) &&
+ (e1->cpu == e2->cpu ||
+ e1->cpu == -1 ||
+ e2->cpu == -1))
+ return true;
+ return false;
+}
+
+static bool __exclusive_event_ok(struct perf_event *event,
+ struct perf_event_context *ctx)
+{
+ struct perf_event *iter_event;
+
+ list_for_each_entry(iter_event, &ctx->event_list, event_entry) {
+ if (exclusive_event_match(iter_event, event))
+ return false;
+ }
+
+ return true;
+}
+
+static bool exclusive_event_ok(struct perf_event *event,
+ struct perf_event_context *ctx)
+{
+ struct pmu *pmu = event->pmu;
+ bool ret;
+
+ if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
+ return true;
+
+ /*
+ * exclusive_cnt <0: cpu
+ * >0: tsk
+ */
+ if (ctx->task) {
+ if (!atomic_inc_unless_negative(&pmu->exclusive_cnt))
+ return false;
+ } else {
+ if (!atomic_dec_unless_positive(&pmu->exclusive_cnt))
+ return false;
+ }
+
+ mutex_lock(&ctx->lock);
+ ret = __exclusive_event_ok(event, ctx);
+ mutex_unlock(&ctx->lock);
+
+ if (!ret) {
+ if (ctx->task)
+ atomic_dec(&pmu->exclusive_cnt);
+ else
+ atomic_inc(&pmu->exclusive_cnt);
+ }
+
+ return ret;
+}
+
+static void exclusive_event_release(struct perf_event *event)
+{
+ struct perf_event_context *ctx = event->ctx;
+ struct pmu *pmu = event->pmu;
+
+ if (!(pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
+ return;
+
+ if (ctx->task)
+ atomic_dec(&pmu->exclusive_cnt);
+ else
+ atomic_inc(&pmu->exclusive_cnt);
+}
+
static void mutex_lock_double(struct mutex *a, struct mutex *b)
{
if (b < a)
@@ -7702,6 +7778,15 @@ SYSCALL_DEFINE5(perf_event_open,
task = NULL;
}
+ if (pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE) {
+ err = -EBUSY;
+ if (group_leader)
+ goto err_context;
+
+ if (!exclusive_event_ok(event, ctx))
+ goto err_context;
+ }
+
/*
* Look up the group leader (we will attach this event to it):
*/
@@ -7903,6 +7988,11 @@ perf_event_create_kernel_counter(struct
goto err_free;
}
+ if (!exclusive_event_ok(event, ctx)) {
+ err = -EBUSY;
+ goto err_context;
+ }
+
WARN_ON_ONCE(ctx->parent_ctx);
mutex_lock(&ctx->mutex);
perf_install_in_context(ctx, event, cpu);
@@ -7911,6 +8001,9 @@ perf_event_create_kernel_counter(struct
return event;
+err_context:
+ perf_unpin_context(ctx);
+ put_ctx(ctx);
err_free:
free_event(event);
err:
--
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