From 6a070573f290f99a6129ac3e13b9df521a1a65de Mon Sep 17 00:00:00 2001 From: Namhyung Kim Date: Fri, 20 Oct 2023 13:47:40 -0700 Subject: perf lock contention: Check race in tstamp elem creation When pelem is NULL, it'd create a new entry with zero data. But it might be preempted by IRQ/NMI just before calling bpf_map_update_elem() then there's a chance to call it twice for the same pid. So it'd be better to use BPF_NOEXIST flag and check the return value to prevent the race. Signed-off-by: Namhyung Kim Acked-by: Ian Rogers Cc: Hao Luo Cc: Song Liu Cc: bpf@vger.kernel.org Link: https://lore.kernel.org/r/20231020204741.1869520-2-namhyung@kernel.org --- tools/perf/util/bpf_skel/lock_contention.bpf.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'tools/perf') diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c index b11179452e19..69d31fd77cd0 100644 --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c @@ -328,7 +328,11 @@ int contention_begin(u64 *ctx) if (pelem == NULL) { struct tstamp_data zero = {}; - bpf_map_update_elem(&tstamp, &pid, &zero, BPF_ANY); + if (bpf_map_update_elem(&tstamp, &pid, &zero, BPF_NOEXIST) < 0) { + __sync_fetch_and_add(&task_fail, 1); + return 0; + } + pelem = bpf_map_lookup_elem(&tstamp, &pid); if (pelem == NULL) { __sync_fetch_and_add(&task_fail, 1); -- cgit v1.2.3