[PATCH v3 06/14] perf, core: always switch pmu specific data during context switch

["Yan, Zheng" <zheng.z.yan@intel.com>]

If two tasks were both forked from the same parent task, Events in
their perf task contexts can be the same. Perf core optimizes context
switch out in this case.

Previous patch inroduces pmu specific data. The data is task specific,
so we should switch the data even when context switch is optimized out.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
---
 kernel/events/core.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index da551c5..d5417e5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2331,6 +2331,7 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn,
 		raw_spin_lock(&ctx->lock);
 		raw_spin_lock_nested(&next_ctx->lock, SINGLE_DEPTH_NESTING);
 		if (context_equiv(ctx, next_ctx)) {
+			void *ctx_data;
 			/*
 			 * XXX do we need a memory barrier of sorts
 			 * wrt to rcu_dereference() of perf_event_ctxp
@@ -2339,6 +2340,11 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn,
 			next->perf_event_ctxp[ctxn] = ctx;
 			ctx->task = next;
 			next_ctx->task = task;
+
+			ctx_data = next_ctx->task_ctx_data;
+			next_ctx->task_ctx_data = ctx->task_ctx_data;
+			ctx->task_ctx_data = ctx_data;
+
 			do_switch = 0;
 
 			perf_event_sync_stat(ctx, next_ctx);
-- 
1.8.5.3