Re: [LTP] hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

[linuxtestproject.agent@gmail.com]

Hi Samir,

On August 18, 2026, Samir Mulani wrote:
> hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

> Migrate the alloc-instantiate-race.c test from libhugetlbfs [1] to LTP
> as hugemmap36.

Could this be corrected to hugemmap42, which is the test added by this
patch?

> +hugemmap42 hugemmap42

Could a second runtest entry exercise "-m private"? Without an option,
setup() defaults to MAP_SHARED, so the new pthread path is not run by the
hugetlb suite.

> +	err = sched_setaffinity(getpid(), mask_size, cpuset);

Could this pass 0 as the pid? sched_setaffinity() applies the mask to the
thread ID supplied in pid. In the MAP_PRIVATE path, getpid() identifies the
thread-group leader for both pthreads, so both racers change the main
thread's affinity and remain unpinned.

> +	p_sync = SAFE_MMAP(NULL, (totpages - 1) * hpage_size,
> +			   PROT_READ | PROT_WRITE, MAP_SHARED, fd_sync, 0);
> +
> +	run_race(race_type);

Could each hugepage in p_sync be written before run_race()? mmap() without
MAP_POPULATE does not fault these pages in. Consequently all free hugepages
remain available to the racers instead of only the final page, and the
allocation race is not exercised. The source test explicitly touches each
page for this reason.

> +	if (p_sync != MAP_FAILED) {
> +		unsigned long totpages = SAFE_READ_MEMINFO(MEMINFO_HPAGE_FREE);
> +
> +		SAFE_MUNMAP(p_sync, totpages * tst_get_hugepage_size());
> +	}

Could the exact length passed to mmap() be saved and reused here? The
current free-page count is not the mapping length. On an abort with the
current code it is one page larger, and munmap() may remove an adjacent
mapping. After the pages are faulted in, a pre-existing hugepage pool can
instead make it smaller and leave part of p_sync mapped.

> +		{NULL, NULL, NULL}

Could this use the standard empty sentinel "{}"? check-hugemmap42 reports
LTP-005 for this options array.

Verdict - Needs revision

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