perf: Fix cgroup scheduling in perf_enable_on_exec()

There is a comment that states that perf_event_context_sched_in() will
also switch in the cgroup events, I cannot find it does so. Therefore
all the resulting logic goes out the window too.

Clean that up.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9d1195af819c0f27843776937ec746602f94f392..e7bda0ed8d40a8283b5121e0c214c4b278929516 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -579,13 +579,7 @@ static inline void perf_cgroup_sched_out(struct task_struct *task,
         * we are holding the rcu lock
         */
        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, NULL);
+       cgrp2 = perf_cgroup_from_task(next, NULL);
 
        /*
         * only schedule out current cgroup events if we know
@@ -611,8 +605,6 @@ static inline void perf_cgroup_sched_in(struct task_struct *prev,
         * we are holding the rcu lock
         */
        cgrp1 = perf_cgroup_from_task(task, NULL);
-
-       /* prev can never be NULL */
        cgrp2 = perf_cgroup_from_task(prev, NULL);
 
        /*
@@ -1450,11 +1442,14 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
 
        if (is_cgroup_event(event)) {
                ctx->nr_cgroups--;
+               /*
+                * Because cgroup events are always per-cpu events, this will
+                * always be called from the right CPU.
+                */
                cpuctx = __get_cpu_context(ctx);
                /*
-                * if there are no more cgroup events
-                * then cler cgrp to avoid stale pointer
-                * in update_cgrp_time_from_cpuctx()
+                * If there are no more cgroup events then clear cgrp to avoid
+                * stale pointer in update_cgrp_time_from_cpuctx().
                 */
                if (!ctx->nr_cgroups)
                        cpuctx->cgrp = NULL;
@@ -3118,15 +3113,6 @@ static void perf_event_enable_on_exec(int ctxn)
        if (!ctx || !ctx->nr_events)
                goto out;
 
-       /*
-        * We must ctxsw out cgroup events to avoid conflict
-        * when invoking perf_task_event_sched_in() later on
-        * in this function. Otherwise we end up trying to
-        * ctxswin cgroup events which are already scheduled
-        * in.
-        */
-       perf_cgroup_sched_out(current, NULL);
-
        raw_spin_lock(&ctx->lock);
        task_ctx_sched_out(ctx);
 
@@ -3144,9 +3130,6 @@ static void perf_event_enable_on_exec(int ctxn)
 
        raw_spin_unlock(&ctx->lock);
 
-       /*
-        * Also calls ctxswin for cgroup events, if any:
-        */
        perf_event_context_sched_in(ctx, ctx->task);
 out:
        local_irq_restore(flags);