[LTP] sched/psi: Add psi_invalid_trigger01 test

[linuxtestproject.agent@gmail.com]

Hi Samir,

On Sat, 24 Oct 2026, Samir Mulani wrote:
> sched/psi: Add psi_invalid_trigger01 test

--- [PATCH 1/4] ---

> +	.needs_kconfigs = (const char *const[]) {
> +		"CONFIG_PSI=y",

Medium: PSI statistics exist in Linux 4.20-5.1, but trigger writes were
introduced in 5.2, so CONFIG_PSI and the setup read do not establish
monitor support. Add .min_kver = "5.2" or equivalent runtime detection
to avoid failing on supported kernels without this interface.

> +		TEST(write(fd, tc->input, len));
> +
> +		if (TST_RET == (long)len)
> +			tst_res(TPASS, "%s: trigger accepted", tc->desc);

Low: Use TST_EXP_VAL(write(fd, tc->input, len), (long)len,
"%s", tc->desc) instead of the manual return-value reporting block.

> +	.needs_root = 1,
> +	.caps = (struct tst_cap []) {
> +		TST_CAP(TST_CAP_REQ, CAP_SYS_RESOURCE),

Low: Document the root/CAP_SYS_RESOURCE requirement for custom trigger
windows in the high-level test description, not only the commit message.

> diff --git a/testcases/kernel/sched/psi/Makefile b/testcases/kernel/sched/psi/Makefile
> +# SPDX-License-Identifier: GPL-2.0-or-later
> +

Low: Add the required copyright line after the SPDX tag.

--- [PATCH 2/4] ---

> +static struct tst_test test = {
> +	.tcnt = ARRAY_SIZE(tests),
> +	.test = run,
> +	.setup = setup,

Medium: This test also needs a monitor-availability gate for PSI-enabled
4.20-5.1 kernels, where setup succeeds but trigger writes are unsupported.
Use .min_kver = "5.2" or equivalent runtime detection.

> +	TST_EXP_FAIL2(WRITE_TRIG(fd, TRIG_B), EBUSY,
> +		      "second write to the same fd");

Medium: This checks the behavior introduced by kernel fix a06247c6804f
("psi: Fix uaf issue when psi trigger is destroyed while being polled").
Add a linux-git regression tag for that fix and explain the relationship
in the commit message; do not skip kernels merely because they lack
the fix.

> +static void (*const tests[])(void) = {
> +	first_write_succeeds,
> +	second_write_ebusy,
> +	dup_fd_shares_trigger,

Low: Use the required struct tcase table and common .test handler,
parameterizing trigger strings, descriptor sharing and expected results
instead of dispatching separate per-case functions.

> +	.needs_root = 1,

Low: Explain the writable PSI interface and custom-window privilege
requirements in the high-level test description.

--- [PATCH 3/4] ---

> +#define PSI_LINE "%7s avg10=%lf avg60=%lf avg300=%lf total=%llu"
> [...]
> +	SAFE_FCLOSE(fp);
> +
> +	if (ret != 10) {

Medium: Supplying total=-1 and an unexpected third line still produces
seven passing results: %llu accepts the sign and the parser ignores
everything after the tenth conversion. Validate unsigned decimal totals,
consume each expected line completely, and reject extra records.

> +	if (n < ARRAY_SIZE(paths))
> +		verify_format(n);
> +	else if (n < 2 * ARRAY_SIZE(paths))
> +		verify_monotonic(n - ARRAY_SIZE(paths));
> +	else
> +		verify_cpu_full_zero();

Low: Replace the index-range dispatch with a struct tcase table describing
each path and check, using the common .test callback.

--- [PATCH 4/4] ---

> +			tst_clock_gettime(CLOCK_MONOTONIC, &start);
> +
> +			if (pwrite(fd, io_buf, IO_SIZE, 0) != IO_SIZE)
> +				tst_brk(TBROK | TERRNO, "pwrite() failed");
> +
> +			tst_clock_gettime(CLOCK_MONOTONIC, &end);
> +			*io_wait_us += tst_timespec_diff_us(end, start);

High: This measures syscall wall time, including CPU work and preemption,
not time blocked on I/O. An O_DIRECT shmem reproduction measured 1995579us
with zero voluntary context switches, yet the test would require 498894us
of I/O pressure; LTP_DEV_FS_TYPE=tmpfs reaches this no-storage path.
Measure actual blocked-I/O time independently or use a controlled
blocking-I/O workload before deriving the expected PSI delta.

> +static char io_buf[IO_SIZE] __attribute__((aligned(4096)));

Medium: A fixed 4KiB alignment is insufficient on supported 64KiB-page
systems with 64KiB-sector Btrfs, which falls back to buffered writes for
this misalignment and invalidates the workload. Allocate a buffer using
the runtime DIO alignment or a suitable runtime page alignment; opening
the file successfully does not validate buffer alignment.

> +	for (i = 0; i < 2; i++) {
> +		if (!SAFE_FORK()) {
> +			join_cgroup();
> +			pin_to_cpu(pin_cpu);
> +
> +			tst_timer_start(CLOCK_MONOTONIC);

Medium: If the parent is delayed between forks for two seconds, the first
worker can finish before the second joins, producing serial workloads
and a false failure on an otherwise idle CPU. Use checkpoints to wait
until both workers have joined and pinned themselves, then release both
before starting their workload timers.

> +			if (pwrite(fd, io_buf, IO_SIZE, 0) != IO_SIZE)
> +				tst_brk(TBROK | TERRNO, "pwrite() failed");

Low: Use SAFE_PWRITE(SAFE_WRITE_ALL, fd, io_buf, IO_SIZE, 0) for this
workload operation; the subject under test is PSI accounting, not pwrite.

> +static void (*const tests[])(void) = {
> +	verify_cpu,
> +	verify_memory,
> +	verify_io,

Low: Use a struct tcase table and common .test handler rather than
dispatching separate per-case functions.

> +	.needs_root = 1,

Low: Document the cgroup/controller and test-filesystem setup as the
reason for requiring root in the high-level description.

> diff --git a/testcases/kernel/sched/psi/.gitignore b/testcases/kernel/sched/psi/.gitignore
>  /psi_proc_format01
> +/psi_accounting01

Low: Keep the entries sorted; /psi_accounting01 belongs first.

Verdict - Needs revision

---
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LTP AI Reviewer