Re: hugemmap36: Migrating the libhugetlbfs/testcases/truncate_above_4GB.c test v6

Hi Pavithra,

On Sat, 04 Apr 2026, Pavithra <[email protected]> wrote:
> hugemmap36: Migrating the libhugetlbfs/testcases/truncate_above_4GB.c test v6

The "v6" revision tag belongs in the email subject only, not in the
committed subject line. The subject should also use imperative mood:

  hugemmap36: Migrate the libhugetlbfs/testcases/truncate_above_4GB.c test

> +static void sigbus_handler_fail(int signum LTP_ATTRIBUTE_UNUSED,
> +				siginfo_t *si LTP_ATTRIBUTE_UNUSED,
> +				void *uc LTP_ATTRIBUTE_UNUSED)
> +{
> +	siglongjmp(sig_escape, 17);
> +}

This handler does not record the unexpected SIGBUS in any way. The
caller uses it here:

> +	SAFE_SIGACTION(SIGBUS, &sa_fail, NULL);
> +	if (sigsetjmp(sig_escape, 1) == 0)
> +		if (*pi != 1) {
> +			tst_res(TFAIL, "Data 1 has changed!");
> +			goto cleanup;
> +		}

If SIGBUS fires on `*pi` - which is exactly the kernel bug being tested
(the low-offset page was incorrectly truncated) - siglongjmp returns 17,
so `sigsetjmp(...) == 0` is false, the TFAIL block is skipped entirely,
and execution falls through.

The code then reaches the sa_pass / `*qi` block, `*qi` triggers SIGBUS,
test_pass is set to 1, and the test reports TPASS. The test passes when
the kernel bug is present.

sigbus_handler_fail needs to set a flag (e.g. test_pass = -1) so that
after the first sigsetjmp block the caller can detect the unexpected
SIGBUS and report TFAIL before proceeding.

> + * Test for a bug where truncating hugepage files at offsets >= 4GB on
> + * 32-bit systems could incorrectly truncate lower pages due to a
> + * misconversion of hugetlb_vmtruncate_list to a prio_tree.
...
> +	.needs_root = 1,

The doc-comment block does not explain why root is required. Ground
Rule 4 requires that the reason be stated there.

Verdict - Needs revision

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