[RFC][PATCH 8/8] perf/x86: Add sanity checks to x86_schedule_events()

[Peter Zijlstra <peterz@infradead.org>]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/events/core.c |   21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -855,17 +855,30 @@ int x86_schedule_events(struct cpu_hw_ev
 	struct event_constraint *c;
 	unsigned long used_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
 	struct perf_event *e;
-	int i, wmin, wmax, unsched = 0;
+	int n0, i, wmin, wmax, unsched = 0;
 	struct hw_perf_event *hwc;
 
 	bitmap_zero(used_mask, X86_PMC_IDX_MAX);
 
+	/*
+	 * Compute the number of events already present; see x86_pmu_add(),
+	 * validate_group() and x86_pmu_commit_txn(). For the former two
+	 * cpuc->n_events hasn't been updated yet, while for the latter
+	 * cpuc->n_txn contains the number of events added in the current
+	 * transaction.
+	 */
+	n0 = cpuc->n_events;
+	if (cpuc->txn_flags & PERF_PMU_TXN_ADD)
+		n0 -= cpuc->n_txn;
+
 	if (x86_pmu.start_scheduling)
 		x86_pmu.start_scheduling(cpuc);
 
 	for (i = 0, wmin = X86_PMC_IDX_MAX, wmax = 0; i < n; i++) {
 		c = cpuc->event_constraint[i];
 
+		WARN_ON_ONCE((c && i >= n0) || (!c && i < n0));
+
 		/*
 		 * Request constraints for new events; or for those events that
 		 * have a dynamic constraint due to the HT workaround -- for
@@ -945,11 +958,7 @@ int x86_schedule_events(struct cpu_hw_ev
 				x86_pmu.commit_scheduling(cpuc, i, assign[i]);
 		}
 	} else {
-		i = cpuc->n_events;
-		if (cpuc->txn_flags & PERF_PMU_TXN_ADD)
-			i -= cpuc->n_txn;
-
-		for (; i < n; i++) {
+		for (i = n0; i < n; i++) {
 			e = cpuc->event_list[i];
 
 			/*