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Message-ID: <aK2XS_GhLw1EQ2ml@J2N7QTR9R3>
Date: Tue, 26 Aug 2025 12:15:23 +0100
From: Mark Rutland <mark.rutland@....com>
To: Robin Murphy <robin.murphy@....com>
Cc: peterz@...radead.org, mingo@...hat.com, will@...nel.org,
acme@...nel.org, namhyung@...nel.org,
alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
irogers@...gle.com, adrian.hunter@...el.com,
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linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 02/19] perf/hisilicon: Fix group validation
On Wed, Aug 13, 2025 at 06:00:54PM +0100, Robin Murphy wrote:
> The group validation logic shared by the HiSilicon HNS3/PCIe drivers is
> a bit off, in that given a software group leader, it will consider that
> event *in place of* the actual new event being opened. At worst this
> could theoretically allow an unschedulable group if the software event
> config happens to look like one of the hardware siblings.
>
> The uncore framework avoids that particular issue,
What is "the uncore framework"? I'm not sure exactly what you're
referring to, nor how that composes with the problem described above.
> but all 3 also share the common issue of not preventing racy access to
> the sibling list,
Can you please elaborate on this racy access to the silbing list? I'm
not sure exactly what you're referring to.
> and some redundant checks which can be cleaned up.
>
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
> drivers/perf/hisilicon/hisi_pcie_pmu.c | 17 ++++++-----------
> drivers/perf/hisilicon/hisi_uncore_pmu.c | 23 +++++++----------------
> drivers/perf/hisilicon/hns3_pmu.c | 17 ++++++-----------
> 3 files changed, 19 insertions(+), 38 deletions(-)
>
> diff --git a/drivers/perf/hisilicon/hisi_pcie_pmu.c b/drivers/perf/hisilicon/hisi_pcie_pmu.c
> index c5394d007b61..3b0b2f7197d0 100644
> --- a/drivers/perf/hisilicon/hisi_pcie_pmu.c
> +++ b/drivers/perf/hisilicon/hisi_pcie_pmu.c
> @@ -338,21 +338,16 @@ static bool hisi_pcie_pmu_validate_event_group(struct perf_event *event)
> int counters = 1;
> int num;
>
> - event_group[0] = leader;
> - if (!is_software_event(leader)) {
> - if (leader->pmu != event->pmu)
> - return false;
> + if (leader == event)
> + return true;
>
> - if (leader != event && !hisi_pcie_pmu_cmp_event(leader, event))
> - event_group[counters++] = event;
> - }
> + event_group[0] = event;
> + if (leader->pmu == event->pmu && !hisi_pcie_pmu_cmp_event(leader, event))
> + event_group[counters++] = leader;
Looking at this, the existing logic to share counters (which
hisi_pcie_pmu_cmp_event() is trying to permit) looks to be bogus, given
that the start/stop callbacks will reprogram the HW counters (and hence
can fight with one another).
I suspect that can be removed *entirely*, and this can be simplified
down to allocating N counters, without a quadratic event comparison. We
don't try to share counters in other PMU drivers, and there was no
rationale for trying to do this when this wa introduced in commit:
8404b0fbc7fbd42e ("drivers/perf: hisi: Add driver for HiSilicon PCIe PMU")
The 'link' tag in that comment goes to v13, which doesn't link to prior
postings, so I'm not going to dig further.
Mark.
>
> for_each_sibling_event(sibling, event->group_leader) {
> - if (is_software_event(sibling))
> - continue;
> -
> if (sibling->pmu != event->pmu)
> - return false;
> + continue;
>
> for (num = 0; num < counters; num++) {
> /*
> diff --git a/drivers/perf/hisilicon/hisi_uncore_pmu.c b/drivers/perf/hisilicon/hisi_uncore_pmu.c
> index a449651f79c9..3c531b36cf25 100644
> --- a/drivers/perf/hisilicon/hisi_uncore_pmu.c
> +++ b/drivers/perf/hisilicon/hisi_uncore_pmu.c
> @@ -101,26 +101,17 @@ static bool hisi_validate_event_group(struct perf_event *event)
> /* Include count for the event */
> int counters = 1;
>
> - if (!is_software_event(leader)) {
> - /*
> - * We must NOT create groups containing mixed PMUs, although
> - * software events are acceptable
> - */
> - if (leader->pmu != event->pmu)
> - return false;
> + if (leader == event)
> + return true;
>
> - /* Increment counter for the leader */
> - if (leader != event)
> - counters++;
> - }
> + /* Increment counter for the leader */
> + if (leader->pmu == event->pmu)
> + counters++;
>
> for_each_sibling_event(sibling, event->group_leader) {
> - if (is_software_event(sibling))
> - continue;
> - if (sibling->pmu != event->pmu)
> - return false;
> /* Increment counter for each sibling */
> - counters++;
> + if (sibling->pmu == event->pmu)
> + counters++;
> }
>
> /* The group can not count events more than the counters in the HW */
> diff --git a/drivers/perf/hisilicon/hns3_pmu.c b/drivers/perf/hisilicon/hns3_pmu.c
> index c157f3572cae..382e469257f9 100644
> --- a/drivers/perf/hisilicon/hns3_pmu.c
> +++ b/drivers/perf/hisilicon/hns3_pmu.c
> @@ -1058,21 +1058,16 @@ static bool hns3_pmu_validate_event_group(struct perf_event *event)
> int counters = 1;
> int num;
>
> - event_group[0] = leader;
> - if (!is_software_event(leader)) {
> - if (leader->pmu != event->pmu)
> - return false;
> + if (leader == event)
> + return true;
>
> - if (leader != event && !hns3_pmu_cmp_event(leader, event))
> - event_group[counters++] = event;
> - }
> + event_group[0] = event;
> + if (leader->pmu == event->pmu && !hns3_pmu_cmp_event(leader, event))
> + event_group[counters++] = leader;
>
> for_each_sibling_event(sibling, event->group_leader) {
> - if (is_software_event(sibling))
> - continue;
> -
> if (sibling->pmu != event->pmu)
> - return false;
> + continue;
>
> for (num = 0; num < counters; num++) {
> /*
> --
> 2.39.2.101.g768bb238c484.dirty
>
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