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Message-ID: <20250515181042.555189-1-namhyung@kernel.org>
Date: Thu, 15 May 2025 11:10:42 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Arnaldo Carvalho de Melo <acme@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Kan Liang <kan.liang@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
linux-perf-users@...r.kernel.org,
Song Liu <song@...nel.org>,
bpf@...r.kernel.org,
Alexei Starovoitov <ast@...nel.org>
Subject: [PATCH] perf lock contention: Reject more than 10ms delays for safety
Delaying kernel operations can be dangerous and the kernel may kill
(non-sleepable) BPF programs running for long in the future.
Limit the max delay to 10ms and update the document about it.
$ sudo ./perf lock con -abl -J 100000us@...oup_mutex true
lock delay is too long: 100000us (> 10ms)
Usage: perf lock contention [<options>]
-J, --inject-delay <TIME@...C>
Inject delays to specific locks
Suggested-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
tools/perf/Documentation/perf-lock.txt | 8 ++++++--
tools/perf/builtin-lock.c | 5 +++++
2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/tools/perf/Documentation/perf-lock.txt b/tools/perf/Documentation/perf-lock.txt
index 2d9aecf630422aa6..c17b3e318169f9dc 100644
--- a/tools/perf/Documentation/perf-lock.txt
+++ b/tools/perf/Documentation/perf-lock.txt
@@ -224,8 +224,12 @@ CONTENTION OPTIONS
only with -b/--use-bpf.
The 'time' is specified in nsec but it can have a unit suffix. Available
- units are "ms" and "us". Note that it will busy-wait after it gets the
- lock. Please use it at your own risk.
+ units are "ms", "us" and "ns". Currently it accepts up to 10ms of delays
+ for safety reasons.
+
+ Note that it will busy-wait after it gets the lock. Delaying locks can
+ have significant consequences including potential kernel crashes. Please
+ use it at your own risk.
SEE ALSO
diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index 41f6f3d2b779b986..3b3ade7a39cad01f 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -2537,6 +2537,11 @@ static bool add_lock_delay(char *spec)
return false;
}
+ if (duration > 10 * 1000 * 1000) {
+ pr_err("lock delay is too long: %s (> 10ms)\n", spec);
+ return false;
+ }
+
tmp = realloc(delays, (nr_delays + 1) * sizeof(*delays));
if (tmp == NULL) {
pr_err("Memory allocation failure\n");
--
2.49.0.1101.gccaa498523-goog
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