Re: [PATCH v2 RESEND] perf/lock: enable end-timestamp accounting for cgroup aggregation

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Incomplete lock contentions for per-CPU locks (spinlocks/rwlocks) are silently dropped when using cgroup aggregation due to an unmodified early return in `account_end_timestamp()`.
--

commit 9be2409410efd2d4d44f23abbecf590bbbc25d34
Author: Suchit Karunakaran <suchitkarunakaran@gmail.com>

perf/lock: enable end-timestamp accounting for cgroup aggregation

This commit enables end-timestamp accounting for cgroup aggregation by
tracking the cgroup_id in the BPF program during contention_begin. It
updates update_lock_stat() in userspace and contention_end() in BPF to
use this recorded cgroup context instead of fetching it dynamically.

> diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
> index cbd7435579fea..1a5bd2ff8ee4c 100644
> --- a/tools/perf/util/bpf_lock_contention.c
> +++ b/tools/perf/util/bpf_lock_contention.c
> @@ -463,8 +463,8 @@ static void update_lock_stat(int map_fd, int pid, u64 end_ts,
>  		stat_key.lock_addr_or_cgroup = ts_data->lock;
>  		break;
>  	case LOCK_AGGR_CGROUP:
> -		/* TODO */
> -		return;
> +		stat_key.lock_addr_or_cgroup = ts_data->cgroup_id;
> +		break;
>  	default:
>  		return;
>  	}

[Severity: Medium]
Since this patch enables end-timestamp accounting for cgroup aggregation,
should the early return for LOCK_AGGR_CGROUP in account_end_timestamp()
also be removed?

tools/perf/util/bpf_lock_contention.c:account_end_timestamp() {
        ...
        /* Now it'll check per-cpu tstamp map which doesn't have TID. */
        if (aggr_mode == LOCK_AGGR_TASK || aggr_mode == LOCK_AGGR_CGROUP)
                return;
        ...
}

Without removing this check, incomplete lock contentions for per-CPU
locks (like spinlocks and rwlocks) appear to be silently skipped when
using cgroup aggregation.

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260530195940.78700-1-suchitkarunakaran@gmail.com?part=1