perf/core: Robustify the perf_cgroup_from_task() RCU checks

This patch reinforces the lockdep checks performed by
perf_cgroup_from_tsk() by passing the perf_event_context
whenever possible. It is okay to not hold the RCU read lock
when we know we hold the ctx->lock. This patch makes sure this
property holds.

In some functions, such as perf_cgroup_sched_in(), we do not
pass the context because we are sure we are holding the RCU
read lock.

Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: edumazet@google.com
Link: http://lkml.kernel.org/r/1447322404-10920-3-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

3 files changed, 18 insertions, 10 deletions

diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
index 377e8f8ed391..a316ca96f1b6 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
@@ -298,7 +298,7 @@ static bool __match_event(struct perf_event *a, struct perf_event *b)
 static inline struct perf_cgroup *event_to_cgroup(struct perf_event *event)
 {
         if (event->attach_state & PERF_ATTACH_TASK)
-                return perf_cgroup_from_task(event->hw.target);
+                return perf_cgroup_from_task(event->hw.target, event->ctx);
 
         return event->cgrp;
 }
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index d841d33bcdc9..f9828a48f16a 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -697,9 +697,11 @@ struct perf_cgroup {
  * if there is no cgroup event for the current CPU context.
  */
 static inline struct perf_cgroup *
-perf_cgroup_from_task(struct task_struct *task)
+perf_cgroup_from_task(struct task_struct *task, struct perf_event_context *ctx)
 {
-        return container_of(task_css(task, perf_event_cgrp_id),
+        return container_of(task_css_check(task, perf_event_cgrp_id,
+                                           ctx ? lockdep_is_held(&ctx->lock)
+                                               : true),
                             struct perf_cgroup, css);
 }
 #endif /* CONFIG_CGROUP_PERF */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 60e71ca42c22..1ac857aff7b0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -435,7 +435,7 @@ static inline void update_cgrp_time_from_event(struct perf_event *event)
         if (!is_cgroup_event(event))
                 return;
 
-        cgrp = perf_cgroup_from_task(current);
+        cgrp = perf_cgroup_from_task(current, event->ctx);
         /*
          * Do not update time when cgroup is not active
          */
@@ -458,7 +458,7 @@ perf_cgroup_set_timestamp(struct task_struct *task,
         if (!task || !ctx->nr_cgroups)
                 return;
 
-        cgrp = perf_cgroup_from_task(task);
+        cgrp = perf_cgroup_from_task(task, ctx);
         info = this_cpu_ptr(cgrp->info);
         info->timestamp = ctx->timestamp;
 }
@@ -521,8 +521,10 @@ static void perf_cgroup_switch(struct task_struct *task, int mode)
                                  * set cgrp before ctxsw in to allow
                                  * event_filter_match() to not have to pass
                                  * task around
+                                 * we pass the cpuctx->ctx to perf_cgroup_from_task()
+                                 * because cgorup events are only per-cpu
                                  */
-                                cpuctx->cgrp = perf_cgroup_from_task(task);
+                                cpuctx->cgrp = perf_cgroup_from_task(task, &cpuctx->ctx);
                                 cpu_ctx_sched_in(cpuctx, EVENT_ALL, task);
                         }
                         perf_pmu_enable(cpuctx->ctx.pmu);
@@ -542,15 +544,17 @@ static inline void perf_cgroup_sched_out(struct task_struct *task,
         rcu_read_lock();
         /*
          * we come here when we know perf_cgroup_events > 0
+         * we do not need to pass the ctx here because we know
+         * we are holding the rcu lock
          */
-        cgrp1 = perf_cgroup_from_task(task);
+        cgrp1 = perf_cgroup_from_task(task, NULL);
 
         /*
          * next is NULL when called from perf_event_enable_on_exec()
          * that will systematically cause a cgroup_switch()
          */
         if (next)
-                cgrp2 = perf_cgroup_from_task(next);
+                cgrp2 = perf_cgroup_from_task(next, NULL);
 
         /*
          * only schedule out current cgroup events if we know
@@ -572,11 +576,13 @@ static inline void perf_cgroup_sched_in(struct task_struct *prev,
         rcu_read_lock();
         /*
          * we come here when we know perf_cgroup_events > 0
+         * we do not need to pass the ctx here because we know
+         * we are holding the rcu lock
          */
-        cgrp1 = perf_cgroup_from_task(task);
+        cgrp1 = perf_cgroup_from_task(task, NULL);
 
         /* prev can never be NULL */
-        cgrp2 = perf_cgroup_from_task(prev);
+        cgrp2 = perf_cgroup_from_task(prev, NULL);
 
         /*
          * only need to schedule in cgroup events if we are changing