perf: Make ctx->is_active and cpuctx->task_ctx consistent

For no apparent reason and to great confusion the rules for
ctx->is_active and cpuctx->task_ctx are different. This means that its
not always possible to find all active (task) contexts.

Fix this such that if ctx->is_active gets set, we also set (or verify)
cpuctx->task_ctx.

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>

1 files changed, 14 insertions, 7 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 935aefd16354..89b47050a2e8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2329,6 +2329,12 @@ static void ctx_sched_out(struct perf_event_context *ctx,
         lockdep_assert_held(&ctx->lock);
 
         ctx->is_active &= ~event_type;
+        if (ctx->task) {
+                WARN_ON_ONCE(cpuctx->task_ctx != ctx);
+                if (!ctx->is_active)
+                        cpuctx->task_ctx = NULL;
+        }
+
         if (likely(!ctx->nr_events))
                 return;
 
@@ -2629,7 +2635,6 @@ static void task_ctx_sched_out(struct perf_cpu_context *cpuctx,
                 return;
 
         ctx_sched_out(ctx, cpuctx, EVENT_ALL);
-        cpuctx->task_ctx = NULL;
 }
 
 /*
@@ -2712,6 +2717,13 @@ ctx_sched_in(struct perf_event_context *ctx,
         lockdep_assert_held(&ctx->lock);
 
         ctx->is_active |= event_type;
+        if (ctx->task) {
+                if (!is_active)
+                        cpuctx->task_ctx = ctx;
+                else
+                        WARN_ON_ONCE(cpuctx->task_ctx != ctx);
+        }
+
         if (likely(!ctx->nr_events))
                 return;
 
@@ -2756,12 +2768,7 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
          * cpu flexible, task flexible.
          */
         cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
-
-        if (ctx->nr_events)
-                cpuctx->task_ctx = ctx;
-
-        perf_event_sched_in(cpuctx, cpuctx->task_ctx, task);
-
+        perf_event_sched_in(cpuctx, ctx, task);
         perf_pmu_enable(ctx->pmu);
         perf_ctx_unlock(cpuctx, ctx);
 }