[PATCH] perf/arm-dmc620: Fix lockdep assert in ->event_init()
Robin Murphy
robin.murphy at arm.com
Wed May 15 05:12:02 PDT 2024
On 2024-05-14 7:00 pm, Namhyung Kim wrote:
> for_each_sibling_event() checks leader's ctx but it doesn't have the ctx
> yet if it's the leader. Like in perf_event_validate_size(), we should
> skip checking siblings in that case.
Ugh, looking around for_each_sibling_event() sites, it looks like there
are a fair few other drivers using this pattern as well :(
I'd love for groups to be less horribly complicated, but I think I can
follow the underlying reasoning here. I suppose one could argue that the
assertion could take into account that there's nothing to protect in the
case where event->ctx is still NULL, since nobody else should be able to
touch the event's own empty sibling list at this point before
perf_event_open() has even returned. However by the same token there's
also no real reason for drivers *not* to return early when they equally
can tell that the sibling list must be empty, and indeed that seems to
be a fairly common pattern too, so I see no issue with fixing up all the
offending drivers for consistency either.
Reviewed-by: Robin Murphy <robin.murphy at arm.com>
> Fixes: f3c0eba287049 ("perf: Add a few assertions")
> Reported-by: Greg Thelen <gthelen at google.com>
> Cc: Robin Murphy <robin.murphy at arm.com>
> Cc: Tuan Phan <tuanphan at os.amperecomputing.com>
> Signed-off-by: Namhyung Kim <namhyung at kernel.org>
> ---
> drivers/perf/arm_dmc620_pmu.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/perf/arm_dmc620_pmu.c b/drivers/perf/arm_dmc620_pmu.c
> index 8a81be2dd5ec..88c17c1d6d49 100644
> --- a/drivers/perf/arm_dmc620_pmu.c
> +++ b/drivers/perf/arm_dmc620_pmu.c
> @@ -542,12 +542,16 @@ static int dmc620_pmu_event_init(struct perf_event *event)
> if (event->cpu < 0)
> return -EINVAL;
>
> + hwc->idx = -1;
> +
> + if (event->group_leader == event)
> + return 0;
> +
> /*
> * We can't atomically disable all HW counters so only one event allowed,
> * although software events are acceptable.
> */
> - if (event->group_leader != event &&
> - !is_software_event(event->group_leader))
> + if (!is_software_event(event->group_leader))
> return -EINVAL;
>
> for_each_sibling_event(sibling, event->group_leader) {
> @@ -556,7 +560,6 @@ static int dmc620_pmu_event_init(struct perf_event *event)
> return -EINVAL;
> }
>
> - hwc->idx = -1;
> return 0;
> }
>
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