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

Hi Samir,

On Aug 21, 2026, Samir Mulani wrote:
> hugemmap: Migrate alloc-instantiate-race test from libhugetlbfs

> +		SAFE_PTHREAD_CREATE(&thread1, NULL, thread_racer, &ri1);
> +		SAFE_PTHREAD_CREATE(&thread2, NULL, thread_racer, &ri2);
> +
> +		/* Wake both threads to start the race simultaneously */
> +		TST_CHECKPOINT_WAKE2(0, 2);

Medium: Could the MAP_PRIVATE pthread race run in a child process so that
the parent can translate SIGBUS into TFAIL?

The allocation failure under test makes hugetlb_no_page() return
VM_FAULT_SIGBUS. An unhandled SIGBUS in either thread terminates the whole
thread group, after which LTP's check_child_status() reports TBROK instead
of identifying the kernel regression as TFAIL. The MAP_SHARED variant
already translates signal deaths in its child racers.

> +	cpu_set_t cpuset;
> +	int total_cpus, cpu_idx;
> +
> +	CPU_ZERO(&cpuset);
> +
> +	total_cpus = get_nprocs_conf();
> +
> +	if (sched_getaffinity(0, sizeof(cpu_set_t), &cpuset) == -1)
> +		tst_brk(TBROK | TERRNO, "sched_getaffinity() failed");

Medium: Could this use a dynamic mask sized with tst_ncpus_max(),
CPU_ALLOC(), and CPU_ALLOC_SIZE()?

sched_getaffinity() returns EINVAL when the supplied buffer is smaller
than the kernel affinity mask. A kernel supporting more than CPU_SETSIZE
CPUs therefore produces TBROK even when the test has two usable CPUs.

> +#include <pthread.h>
> +#include "tst_test.h"
> +#include "tst_safe_pthread.h"

Medium: Could hugemmap42 be added to the Makefile's existing
CFLAGS += -pthread rule?

The test links on modern glibc because libpthread was merged into libc,
but older supported libc versions need -pthread to resolve the symbols
used by the safe pthread wrappers.

> +/hugetlb/hugemmap/hugemmap42

Low: Could this entry be moved to a leaf
testcases/kernel/mem/hugetlb/hugemmap/.gitignore?

New test binaries should be ignored in their own test directory rather
than in testcases/kernel/mem/.gitignore.

> +	.hugepages = {2, TST_NEEDS},
> +	.forks_child = 1,
> +	.needs_checkpoints = 1,
> +	.min_cpus = 2,
> +};

Low: Could the kernel fix for this regression be added as a linux-git
tag so that failures provide the missing-fix hint?

> + * other racing process.
> + */
> [...]
> +	.needs_root = 1,

Low: Could the exported description explain that root is needed to
reserve hugepages and mount hugetlbfs?

> +	SAFE_CLOSE(fd_race);
> +	fd_race = -1;
> [...]
> +	if (fd_race >= 0)
> +		SAFE_CLOSE(fd_race);

Low: Could the redundant assignment be removed and the cleanup guard use
fd_race != -1, with the same changes for fd_sync?

SAFE_CLOSE() already sets the descriptor to -1, and != -1 is the LTP
descriptor-validity convention.

Verdict - Needs revision

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