Re: [PATCH v3 03/19] perf test: Add a workload that forces context switches

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Calling exit(1) on I/O failure in the parent process abruptly terminates the test wrapper and bypasses workload control cleanup.
--

commit 4bc96eb1d44f39f8252cd4bbe7f402600bc7ca26
Author: James Clark <james.clark@linaro.org>

perf test: Add a workload that forces context switches

This workload launches two processes that block when reading and writing
to each other forcing the other process to be scheduled for each
read/write pair.

> diff --git a/tools/perf/tests/workloads/context_switch_loop.c b/tools/perf/tests/workloads/context_switch_loop.c
> new file mode 100644
> index 0000000000000..173d770ae6192
> --- /dev/null
> +++ b/tools/perf/tests/workloads/context_switch_loop.c
> @@ -0,0 +1,101 @@

[ ... ]

> +#define write_block(fd) \
> +	do { \
> +		if (write(fd, &buf, 1) <= 0) \
> +			exit(1); \
> +	} while (0)
> +
> +#define read_block(fd) \
> +	do { \
> +		if (read(fd, &buf, 1) <= 0) \
> +			exit(1); \
> +	} while (0)

[ ... ]

> +	if (!proc1_pid) {
> +		close(a_to_b[0]);
> +		close(b_to_a[1]);
> +		prctl(PR_SET_NAME, "proc1", 0, 0, 0);
> +		context_switch_loop_proc1(b_to_a[0], a_to_b[1]);
> +		close(a_to_b[1]);
> +		close(b_to_a[0]);
> +		exit(0);
> +	}
> +
> +	close(a_to_b[1]);
> +	close(b_to_a[0]);
> +	prctl(PR_SET_NAME, "proc2", 0, 0, 0);
> +	context_switch_loop_proc2(a_to_b[0], b_to_a[1]);

[Severity: Medium]
Since context_switch_loop_proc2() runs in the parent process, does calling
exit(1) on I/O failures abruptly terminate the entire perf test wrapper?

If write_block() or read_block() encounter an error like EINTR, they call
exit(1) directly. Because context_switch_loop_proc2() is executed in the main
process rather than a forked child, this bypasses the workload control cleanup
in run_workload().

Should the parent process return an error code instead of calling exit(1) so
perf test can clean up gracefully?

> +	close(a_to_b[0]);
> +	close(b_to_a[1]);
> +
> +	if (waitpid(proc1_pid, &status, 0) != proc1_pid || !WIFEXITED(status) ||
> +	    WEXITSTATUS(status))
> +		return 1;
> +
> +	return 0;
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260603-james-cs-context-tracking-fix-v3-0-c392945d9ed5@linaro.org?part=3