On Tue, Jul 04, 2023 at 11:15:15AM -0700, Namhyung Kim wrote:
On SPR, the load latency event needs an auxiliary event in the same group to work properly. There's a check in intel_pmu_hw_config() for this to iterate sibling events and find a mem-loads-aux event.
The for_each_sibling_event() has a lockdep assert to make sure if it disabled hardirq or hold leader->ctx->mutex. This works well if the given event has a separate leader event since perf_try_init_event() grabs the leader->ctx->mutex to protect the sibling list. But it can cause a problem when the event itself is a leader since the event is not initialized yet and there's no ctx for the event.
Actually I got a lockdep warning when I run the below command on SPR, but I guess it could be a NULL pointer dereference.
$ perf record -d -e cpu/mem-loads/uP true
The code path to the warning is:
sys_perf_event_open() perf_event_alloc() perf_init_event() perf_try_init_event() x86_pmu_event_init() hsw_hw_config() intel_pmu_hw_config() for_each_sibling_event() lockdep_assert_event_ctx()
We don't need for_each_sibling_event() when it's a standalone event. Let's return the error code directly.
Fixes: f3c0eba28704 ("perf: Add a few assertions") Reported-by: Greg Thelen gthelen@google.com Cc: stable@vger.kernel.org Signed-off-by: Namhyung Kim namhyung@kernel.org
arch/x86/events/intel/core.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c index 0d09245aa8df..933fe4894c32 100644 --- a/arch/x86/events/intel/core.c +++ b/arch/x86/events/intel/core.c @@ -3983,6 +3983,14 @@ static int intel_pmu_hw_config(struct perf_event *event) struct perf_event *leader = event->group_leader; struct perf_event *sibling = NULL;
/** The event is not fully initialized yet and no ctx is set* for the event. Avoid for_each_sibling_event() since it* has a lockdep assert with leader->ctx->mutex.*/
If I understand things correctly, your patch is indeed correct, however I don't much like this comment, does something like:
/* * When this memload event is also the first event (no * group exists yet), then there is no aux event before * it. */
work for you?
if (leader == event)return -ENODATA;- if (!is_mem_loads_aux_event(leader)) { for_each_sibling_event(sibling, leader) { if (is_mem_loads_aux_event(sibling))
-- 2.41.0.255.g8b1d071c50-goog