// https://syzkaller.appspot.com/bug?id=7349616606afa3c986c377792f7ccbf9daae1142
#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <pthread.h>
#include <sys/syscall.h>
#include <sys/sendfile.h>
#include <sys/mman.h>
#include <sys/resource.h>
#include <string.h>
#include <errno.h>

#ifndef SYS_memfd_create
#define SYS_memfd_create 319
#endif

#define NUM_IDLE_THREADS 50
#define NUM_NORMAL_THREADS 150
#define SENDFILE_SIZE (1024 * 1024) // 1MB

void *worker(void *arg) {
    long is_idle = (long)arg;
    
    if (is_idle) {
        struct sched_param param = {0};
        int res = syscall(SYS_sched_setscheduler, syscall(SYS_gettid), SCHED_IDLE, &param);
        if (res < 0) {
            printf("[-] Failed to sched_setscheduler: %s\n", strerror(errno));
        } else {
            printf("[+] sched_setscheduler successful.\n");
        }
    } else {
        int res = setpriority(PRIO_PROCESS, syscall(SYS_gettid), -20);
        if (res < 0) {
            printf("[-] Failed to setpriority: %s\n", strerror(errno));
        } else {
            printf("[+] setpriority successful.\n");
        }
    }

    int fd_in = syscall(SYS_memfd_create, "in", 0);
    if (fd_in < 0) {
        char filename[64];
        sprintf(filename, "/tmp/in_%ld", syscall(SYS_gettid));
        fd_in = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666);
    }
    if (fd_in < 0) {
        printf("[-] Failed to create fd_in: %s\n", strerror(errno));
        exit(1);
    }
    
    int res = ftruncate(fd_in, SENDFILE_SIZE);
    if (res < 0) {
        printf("[-] Failed to ftruncate fd_in: %s\n", strerror(errno));
        exit(1);
    }

    int fd_out = syscall(SYS_memfd_create, "out", 0);
    if (fd_out < 0) {
        char filename[64];
        sprintf(filename, "/tmp/out_%ld", syscall(SYS_gettid));
        fd_out = open(filename, O_RDWR | O_CREAT | O_TRUNC, 0666);
    }
    if (fd_out < 0) {
        printf("[-] Failed to create fd_out: %s\n", strerror(errno));
        exit(1);
    }

    while (1) {
        res = lseek(fd_in, 0, SEEK_SET);
        if (res < 0) {
            printf("[-] Failed to lseek fd_in: %s\n", strerror(errno));
            exit(1);
        }
        
        res = lseek(fd_out, 0, SEEK_SET);
        if (res < 0) {
            printf("[-] Failed to lseek fd_out: %s\n", strerror(errno));
            exit(1);
        }
        
        res = ftruncate(fd_out, 0);
        if (res < 0) {
            printf("[-] Failed to ftruncate fd_out: %s\n", strerror(errno));
            exit(1);
        }
        
        ssize_t sres = sendfile(fd_out, fd_in, NULL, SENDFILE_SIZE);
        if (sres < 0) {
            printf("[-] Failed to sendfile: %s\n", strerror(errno));
            exit(1);
        }
    }
    return NULL;
}

int main(void) {
    printf("[*] Starting reproducer...\n");

    int fd = open("/proc/sys/kernel/panic_on_rcu_stall", O_WRONLY);
    if (fd >= 0) {
        int res = write(fd, "1\n", 2);
        if (res < 0) {
            printf("[-] Failed to write panic_on_rcu_stall: %s\n", strerror(errno));
        } else {
            printf("[+] write panic_on_rcu_stall successful.\n");
        }
        close(fd);
    } else {
        printf("[-] Failed to open panic_on_rcu_stall: %s\n", strerror(errno));
    }

    pthread_t idle_threads[NUM_IDLE_THREADS];
    pthread_t normal_threads[NUM_NORMAL_THREADS];
    
    printf("[*] Creating idle threads...\n");
    for (int i = 0; i < NUM_IDLE_THREADS; i++) {
        int res = pthread_create(&idle_threads[i], NULL, worker, (void *)1);
        if (res != 0) {
            printf("[-] Failed to pthread_create idle thread: %s\n", strerror(res));
            exit(1);
        }
    }
    printf("[+] pthread_create idle threads successful.\n");
    
    usleep(500000);
    
    printf("[*] Creating normal threads...\n");
    for (int i = 0; i < NUM_NORMAL_THREADS; i++) {
        int res = pthread_create(&normal_threads[i], NULL, worker, (void *)0);
        if (res != 0) {
            printf("[-] Failed to pthread_create normal thread: %s\n", strerror(res));
            exit(1);
        }
    }
    printf("[+] pthread_create normal threads successful.\n");
    
    for (int i = 0; i < NUM_IDLE_THREADS; i++) {
        int res = pthread_join(idle_threads[i], NULL);
        if (res != 0) {
            printf("[-] Failed to pthread_join idle thread: %s\n", strerror(res));
            exit(1);
        }
    }
    for (int i = 0; i < NUM_NORMAL_THREADS; i++) {
        int res = pthread_join(normal_threads[i], NULL);
        if (res != 0) {
            printf("[-] Failed to pthread_join normal thread: %s\n", strerror(res));
            exit(1);
        }
    }
    
    return 0;
}