On Sat, Oct 08, 2022 at 11:54:24AM +0530, Ravi Bangoria wrote:

+static void perf_event_swap_task_ctx_data(struct perf_event_context *prev_ctx,
+					  struct perf_event_context *next_ctx)
+{
+	struct perf_event_pmu_context *prev_epc, *next_epc;
+
+	if (!prev_ctx->nr_task_data)
+		return;
+
+	prev_epc = list_first_entry(&prev_ctx->pmu_ctx_list,
+				    struct perf_event_pmu_context,
+				    pmu_ctx_entry);
+	next_epc = list_first_entry(&next_ctx->pmu_ctx_list,
+				    struct perf_event_pmu_context,
+				    pmu_ctx_entry);
+
+	while (&prev_epc->pmu_ctx_entry != &prev_ctx->pmu_ctx_list &&
+	       &next_epc->pmu_ctx_entry != &next_ctx->pmu_ctx_list) {
+
+		WARN_ON_ONCE(prev_epc->pmu != next_epc->pmu);
+
+		/*
+		 * PMU specific parts of task perf context can require
+		 * additional synchronization. As an example of such
+		 * synchronization see implementation details of Intel
+		 * LBR call stack data profiling;
+		 */
+		if (prev_epc->pmu->swap_task_ctx)
+			prev_epc->pmu->swap_task_ctx(prev_epc, next_epc);
+		else
+			swap(prev_epc->task_ctx_data, next_epc->task_ctx_data);

Did I forget to advance the iterators here?

+	}
+}