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@cgroup_mutex true
  lock delay is too long: 100000us (> 10ms)

   Usage: perf lock contention [<options>]

      -J, --inject-delay <TIME@FUNC>
                            Inject delays to specific locks

Suggested-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20250515181042.555189-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/Documentation/perf-lock.txt b/tools/perf/Documentation/perf-lock.txt
index 2d9aecf630422aa6a687500ae8268dc9c80405a2..c17b3e318169f9dc6fa3977101c9f4e5be5400ad 100644 (file)
--- 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 41f6f3d2b779b9861f254bc8901644177bad8eda..3b3ade7a39cad01f0a0cdb5449ebc04e49f798fb 100644 (file)
--- 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");