Re: [PATCH] samples/ftrace: reject zero ftrace-ops call count

On Mon, Jun 8, 2026 at 9:03 PM Steven Rostedt [off-list ref] wrote:

On Tue,  9 Jun 2026 00:44:23 +0000
Samuel Moelius [off-list ref] wrote:

quoted

The ftrace-ops sample exposes nr_function_calls as a module parameter
and uses it as the divisor when printing the measured time per call.
Loading the module with nr_function_calls=0 skips the benchmark loop and
then divides the elapsed time by zero, crashing the kernel during sample
module initialization.

This change is rather pointless, but whatever.

quoted

Reject a zero call count before registering any ftrace ops.

Assisted-by: Codex:gpt-5.5-cyber-preview
Signed-off-by: Samuel Moelius <redacted>
---
 samples/ftrace/ftrace-ops.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/samples/ftrace/ftrace-ops.c b/samples/ftrace/ftrace-ops.c
index 68d6685c80bd..d5adaa61484f 100644
--- a/samples/ftrace/ftrace-ops.c
+++ b/samples/ftrace/ftrace-ops.c

@@ -190,6 +190,11 @@ static int __init ftrace_ops_sample_init(void)
              tracer_irrelevant = ops_func_count;
      }

+     if (!nr_function_calls) {
+             pr_err("nr_function_calls must be non-zero\n");
+             return -EINVAL;

No need to print that the admin did something stupid.

quoted

+     }
+
      pr_info("registering:\n"
              "  relevant ops: %u\n"
              "    tracee: %ps\n"

In fact, I would just change the output to be:

        pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
                nr_function_calls, tracee_relevant,
                period, nr_function_calls ? div_u64(period, nr_function_calls) : -1LL);

and have garbage in, garbage out.

Is it okay to keep the same subject line or should I change it?