From: Namhyung Kim <namhyung@kernel.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>, Jiri Olsa <jolsa@kernel.org>
Cc: Ian Rogers <irogers@google.com>,
Adrian Hunter <adrian.hunter@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-perf-users@vger.kernel.org, Song Liu <song@kernel.org>,
Hao Luo <haoluo@google.com>,
bpf@vger.kernel.org
Subject: [PATCH v3 2/3] perf lock contention: Check race in tstamp elem creation
Date: Fri, 20 Oct 2023 13:47:40 -0700 [thread overview]
Message-ID: <20231020204741.1869520-2-namhyung@kernel.org> (raw)
In-Reply-To: <20231020204741.1869520-1-namhyung@kernel.org>
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 <namhyung@kernel.org>
---
tools/perf/util/bpf_skel/lock_contention.bpf.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
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);
--
2.42.0.655.g421f12c284-goog
next prev parent reply other threads:[~2023-10-20 20:47 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-20 20:47 [PATCH v3 1/3] perf lock contention: Clear lock addr after use Namhyung Kim
2023-10-20 20:47 ` Namhyung Kim [this message]
2023-10-25 4:13 ` [PATCH v3 2/3] perf lock contention: Check race in tstamp elem creation Ian Rogers
2023-10-20 20:47 ` [PATCH v3 3/3] perf lock contention: Use per-cpu array map for spinlocks Namhyung Kim
2023-10-25 4:15 ` Ian Rogers
2023-10-25 4:13 ` [PATCH v3 1/3] perf lock contention: Clear lock addr after use Ian Rogers
2023-10-26 17:11 ` Namhyung Kim
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