perf: Add a few assertions

While auditing 6b959ba22d34 ("perf/core: Fix reentry problem in
perf_output_read_group()") a few spots were found that wanted
assertions.

Notable for_each_sibling_event() relies on exclusion from
modification. This would normally be holding either ctx->lock or
ctx->mutex, however due to how things are constructed disabling IRQs
is a valid and sufficient substitute for ctx->lock.

Another possible site to add assertions would be the various
pmu::{add,del,read,..}() methods, but that's not trivially expressable
in C -- the best option is wrappers, but those are easy enough to
forget.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 00389d5f9241..3e90e454b995 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1468,6 +1468,8 @@ static void __update_context_time(struct perf_event_context *ctx, bool adv)
 {
 	u64 now = perf_clock();
 
+	lockdep_assert_held(&ctx->lock);
+
 	if (adv)
 		ctx->time += now - ctx->timestamp;
 	ctx->timestamp = now;