[PATCH v2] perf/core: Fix installing cgroup event into cpu

[linxiulei]

From: "leilei.lin" <leilei.lin@xxxxxxxxxxxxxxx>

Do not install cgroup event into the CPU context if the cgroup
is not running on this CPU

While there is no task of cgroup running specified CPU, current
kernel still install cgroup event into CPU context, that causes
another cgroup event can't be installed into this CPU.

Signed-off-by: leilei.lin <leilei.lin@xxxxxxxxxxxxxxx>
---
 kernel/events/core.c | 44 +++++++++++++++++++++++++++++++-------------
 1 file changed, 31 insertions(+), 13 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4df5b69..f766b60 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -933,31 +933,36 @@ list_update_cgroup_event(struct perf_event *event,
 {
 	struct perf_cpu_context *cpuctx;
 	struct list_head *cpuctx_entry;
+	struct perf_cgroup *cgrp;
 
 	if (!is_cgroup_event(event))
 		return;
 
-	if (add && ctx->nr_cgroups++)
-		return;
-	else if (!add && --ctx->nr_cgroups)
-		return;
 	/*
 	 * Because cgroup events are always per-cpu events,
 	 * this will always be called from the right CPU.
 	 */
 	cpuctx = __get_cpu_context(ctx);
-	cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
-	/* cpuctx->cgrp is NULL unless a cgroup event is active in this CPU .*/
-	if (add) {
-		struct perf_cgroup *cgrp = perf_cgroup_from_task(current, ctx);
+	cgrp = perf_cgroup_from_task(current, ctx);
 
-		list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
-		if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup))
+	/* cpuctx->cgrp is NULL unless a cgroup event is running in this CPU .*/
+	if (cgroup_is_descendant(cgrp->css.cgroup, event->cgrp->css.cgroup)) {
+		if (add)
 			cpuctx->cgrp = cgrp;
-	} else {
-		list_del(cpuctx_entry);
-		cpuctx->cgrp = NULL;
+		else
+			cpuctx->cgrp = NULL;
 	}
+
+	if (add && ctx->nr_cgroups++)
+		return;
+	else if (!add && --ctx->nr_cgroups)
+		return;
+
+	cpuctx_entry = &cpuctx->cgrp_cpuctx_entry;
+	if (add)
+		list_add(cpuctx_entry, this_cpu_ptr(&cgrp_cpuctx_list));
+	else
+		list_del(cpuctx_entry);
 }
 
 #else /* !CONFIG_CGROUP_PERF */
@@ -2284,6 +2289,7 @@ static int  __perf_install_in_context(void *info)
 	struct perf_event_context *ctx = event->ctx;
 	struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
 	struct perf_event_context *task_ctx = cpuctx->task_ctx;
+	struct perf_cgroup *cgrp;
 	bool reprogram = true;
 	int ret = 0;
 
@@ -2311,6 +2317,18 @@ static int  __perf_install_in_context(void *info)
 		raw_spin_lock(&task_ctx->lock);
 	}
 
+	if (is_cgroup_event(event)) {
+		/*
+		 * Only care about cgroup events.
+		 *
+		 * If only the task belongs to cgroup of this event,
+		 * we will continue the installment
+		 */
+		cgrp = perf_cgroup_from_task(current, ctx);
+		reprogram = cgroup_is_descendant(cgrp->css.cgroup,
+					event->cgrp->css.cgroup);
+	}
+
 	if (reprogram) {
 		ctx_sched_out(ctx, cpuctx, EVENT_TIME);
 		add_event_to_ctx(event, ctx);
-- 
2.8.4.31.g9ed660f