chatgpt's attempt to preproduce the git 2.52.0 clone failure seen on ganesha v9.4/v9.6 exports

main.c

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

static const char *CONFIG_PATH = "config";
static const char *LOCK_PATH   = "config.lock";

static void die(const char *msg) {
    perror(msg);
    exit(1);
}

static void safe_close(int fd, const char *what) {
    if (close(fd) != 0) {
        perror(what);
        exit(1);
    }
}

static void write_full(int fd, const void *buf, size_t len, const char *what) {
    const char *p = buf;
    size_t off = 0;
    while (off < len) {
        ssize_t n = write(fd, p + off, len - off);
        if (n < 0) {
            perror(what);
            exit(1);
        }
        off += (size_t)n;
    }
}

static void dump_hex(const void *buf, size_t len) {
    const unsigned char *p = buf;
    for (size_t i = 0; i < len; i++) {
        printf("%02x", p[i]);
        if ((i + 1) % 16 == 0 || i + 1 == len)
            printf("\n");
        else
            printf(" ");
    }
}

static void write_config_atomically(const char *content, size_t len, bool do_fsync) {
    unlink(LOCK_PATH);

    int fd = open(LOCK_PATH, O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
    if (fd < 0)
        die("open config.lock");

    if (fchmod(fd, 0644) != 0)
        die("fchmod config.lock");

    write_full(fd, content, len, "write config.lock");

    if (do_fsync) {
        if (fsync(fd) != 0)
            die("fsync config.lock");
    }

    safe_close(fd, "close config.lock");

    if (rename(LOCK_PATH, CONFIG_PATH) != 0)
        die("rename config.lock -> config");
}

static void read_once_or_report(int iter, const char *expected, size_t expected_len) {
    int fd = open(CONFIG_PATH, O_RDONLY);
    if (fd < 0)
        die("open config for read");

    char buf[4096];
    memset(buf, 0, sizeof(buf));

    ssize_t n = read(fd, buf, 1024);
    if (n < 0) {
        fprintf(stderr,
                "\nITER %d: read(config) failed: errno=%d (%s)\n",
                iter, errno, strerror(errno));
        safe_close(fd, "close config after failed read");
        exit(2);
    }

    off_t off = lseek(fd, 0, SEEK_CUR);
    if (off == (off_t)-1)
        die("lseek after read");

    printf("iter=%d simple-read: n=%zd off=%lld\n",
           iter, n, (long long)off);

    if ((size_t)n != expected_len || memcmp(buf, expected, expected_len) != 0) {
        fprintf(stderr, "\nITER %d: content mismatch\n", iter);
        fprintf(stderr, "expected_len=%zu got=%zd\n", expected_len, n);
        fprintf(stderr, "expected:\n%.*s\n", (int)expected_len, expected);
        fprintf(stderr, "got:\n%.*s\n", (int)n, buf);
        fprintf(stderr, "got hex:\n");
        dump_hex(buf, (size_t)n);
        safe_close(fd, "close config after mismatch");
        exit(3);
    }

    safe_close(fd, "close config after read");
}

static void git_like_read_mmap_copy(int iter) {
    unlink(LOCK_PATH);

    int lockfd = open(LOCK_PATH, O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
    if (lockfd < 0)
        die("open lockfd for git-like copy");

    if (fchmod(lockfd, 0644) != 0)
        die("fchmod lockfd");

    int fd1 = open(CONFIG_PATH, O_RDONLY);
    if (fd1 < 0)
        die("open fd1");

    int fd2 = open(CONFIG_PATH, O_RDONLY);
    if (fd2 < 0)
        die("open fd2");

    char tmp[1024];
    ssize_t rn;
    struct stat st;

    if (fstat(fd2, &st) != 0)
        die("fstat fd2");

    rn = read(fd2, tmp, sizeof(tmp));
    if (rn < 0) {
        fprintf(stderr,
                "\nITER %d: git-like read(fd2) failed: errno=%d (%s)\n",
                iter, errno, strerror(errno));
        safe_close(fd2, "close fd2 after failed read");
        safe_close(fd1, "close fd1 after failed read");
        safe_close(lockfd, "close lockfd after failed read");
        exit(4);
    }

    printf("iter=%d git-like read(fd2): n=%zd st_size=%lld\n",
           iter, rn, (long long)st.st_size);

    safe_close(fd2, "close fd2");

    if (fstat(fd1, &st) != 0)
        die("fstat fd1");

    void *addr = mmap(NULL, (size_t)st.st_size, PROT_READ, MAP_PRIVATE, fd1, 0);
    if (addr == MAP_FAILED)
        die("mmap fd1");

    safe_close(fd1, "close fd1");

    write_full(lockfd, "[core]\n", 7, "write prefix 1");
    write_full(lockfd, "\tbare = false\n", 14, "write prefix 2");

    ssize_t wn = write(lockfd, addr, (size_t)st.st_size);
    if (wn < 0) {
        fprintf(stderr,
                "\nITER %d: git-like write(lockfd, mmap_addr) failed: errno=%d (%s)\n",
                iter, errno, strerror(errno));
        munmap(addr, (size_t)st.st_size);
        safe_close(lockfd, "close lockfd after failed mmap write");
        exit(5);
    }

    printf("iter=%d git-like mmap-copy write: n=%zd\n", iter, wn);

    if (munmap(addr, (size_t)st.st_size) != 0)
        die("munmap");

    safe_close(lockfd, "close lockfd");
}

int main(int argc, char **argv) {
    int iterations = 1000;
    bool do_fsync = false;
    bool do_git_like = true;

    if (argc > 1)
        iterations = atoi(argv[1]);
    if (argc > 2)
        do_fsync = (atoi(argv[2]) != 0);
    if (argc > 3)
        do_git_like = (atoi(argv[3]) != 0);

    const char *content1 =
        "[core]\n"
        "\trepositoryformatversion = 0\n";

    const char *content2 =
        "[core]\n"
        "\trepositoryformatversion = 0\n"
        "\tfilemode = true\n";

    size_t len1 = strlen(content1);
    size_t len2 = strlen(content2);

    unlink(CONFIG_PATH);
    unlink(LOCK_PATH);

    for (int i = 1; i <= iterations; i++) {
        const char *content = (i & 1) ? content1 : content2;
        size_t len = (i & 1) ? len1 : len2;

        printf("\n=== iter %d write len=%zu ===\n", i, len);

        write_config_atomically(content, len, do_fsync);
        read_once_or_report(i, content, len);

        if (do_git_like)
            git_like_read_mmap_copy(i);
    }

    printf("\ncompleted %d iterations without failure\n", iterations);
    return 0;
}

strace.txt

rook-ceph-demo-nfs-auxtel-jhoblitt-test1:/data/auxtel/gittest$ strace ./c.out
execve("./c.out", ["./c.out"], 0x7ffc4ab71440 /* 16 vars */) = 0
arch_prctl(ARCH_SET_FS, 0x7f8bad9687b8) = 0
set_tid_address(0x7f8bad9688f0)         = 600
brk(NULL)                               = 0x42b000
brk(0x42c000)                           = 0x42c000
readlink("/proc/self/exe", "/data/auxtel/gittest/c.out", 4096) = 26
execve("/lib/ld-musl-x86_64.so.1", ["ld-linux-x86-64.so.2", "--argv0", "./c.out", "--preload", "/lib/libgcompat.so.0 ", "--", "/data/auxtel/gittest/c.out"], 0x7ffd6b647dc8 /* 16 vars */) = 0
arch_prctl(ARCH_SET_FS, 0x7f520c409b28) = 0
set_tid_address(0x7f520c409f90)         = 600
open("/data/auxtel/gittest/c.out", O_RDONLY|O_LARGEFILE) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\2\0>\0\1\0\0\0\360\4@\0\0\0\0\0"..., 960) = 960
mmap(0x400000, 16384, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x400000
mmap(0x401000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED, 3, 0x1000) = 0x401000
mmap(0x402000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x1000) = 0x402000
close(3)                                = 0
brk(NULL)                               = 0x555556ead000
brk(0x555556eaf000)                     = 0x555556eaf000
mmap(0x555556ead000, 4096, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x555556ead000
open("/lib/libgcompat.so.0", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fstat(3, {st_mode=S_IFREG|0755, st_size=67184, ...}) = 0
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 960) = 960
mmap(NULL, 73728, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f520c352000
mmap(0x7f520c359000, 20480, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 3, 0x7000) = 0x7f520c359000
mmap(0x7f520c35e000, 12288, PROT_READ, MAP_PRIVATE|MAP_FIXED, 3, 0xc000) = 0x7f520c35e000
mmap(0x7f520c361000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0xf000) = 0x7f520c361000
mmap(0x7f520c363000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f520c363000
close(3)                                = 0
open("/etc/ld-musl-x86_64.path", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/lib/libucontext.so.1", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/local/lib/libucontext.so.1", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/lib/libucontext.so.1", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fstat(3, {st_mode=S_IFREG|0755, st_size=13936, ...}) = 0
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 960) = 960
mmap(NULL, 20480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f520c34d000
mmap(0x7f520c34e000, 4096, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 3, 0x1000) = 0x7f520c34e000
mmap(0x7f520c34f000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED, 3, 0x2000) = 0x7f520c34f000
mmap(0x7f520c350000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x2000) = 0x7f520c350000
close(3)                                = 0
open("/lib/libobstack.so.1", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/local/lib/libobstack.so.1", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = -1 ENOENT (No such file or directory)
open("/usr/lib/libobstack.so.1", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fstat(3, {st_mode=S_IFREG|0755, st_size=13944, ...}) = 0
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 960) = 960
mmap(NULL, 20480, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f520c348000
mmap(0x7f520c349000, 4096, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED, 3, 0x1000) = 0x7f520c349000
mmap(0x7f520c34a000, 4096, PROT_READ, MAP_PRIVATE|MAP_FIXED, 3, 0x2000) = 0x7f520c34a000
mmap(0x7f520c34b000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x2000) = 0x7f520c34b000
close(3)                                = 0
mprotect(0x7f520c361000, 4096, PROT_READ) = 0
mprotect(0x7f520c406000, 4096, PROT_READ) = 0
mprotect(0x7f520c350000, 4096, PROT_READ) = 0
mprotect(0x7f520c34b000, 4096, PROT_READ) = 0
mprotect(0x402000, 4096, PROT_READ)     = 0
unlink("config")                        = 0
unlink("config.lock")                   = -1 ENOENT (No such file or directory)
ioctl(1, TIOCGWINSZ, {ws_row=48, ws_col=190, ws_xpixel=0, ws_ypixel=0}) = 0
writev(1, [{iov_base="\n", iov_len=1}], 1
) = 1
writev(1, [{iov_base="=== iter 1 write len=36", iov_len=23}, {iov_base=" ===\n", iov_len=5}], 2=== iter 1 write len=36 ===
) = 28
unlink("config.lock")                   = -1 ENOENT (No such file or directory)
open("config.lock", O_RDWR|O_CREAT|O_EXCL|O_LARGEFILE|O_CLOEXEC, 0666) = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fchmod(3, 0644)                         = 0
write(3, "[core]\n\trepositoryformatversion "..., 36) = 36
close(3)                                = 0
rename("config.lock", "config")         = 0
open("config", O_RDONLY|O_LARGEFILE)    = 3
read(3, "[core]\n\trepositoryformatversion "..., 1024) = 36
lseek(3, 0, SEEK_CUR)                   = 36
writev(1, [{iov_base="iter=1 simple-read: n=36 off=36", iov_len=31}, {iov_base="\n", iov_len=1}], 2iter=1 simple-read: n=36 off=36
) = 32
close(3)                                = 0
unlink("config.lock")                   = -1 ENOENT (No such file or directory)
open("config.lock", O_RDWR|O_CREAT|O_EXCL|O_LARGEFILE|O_CLOEXEC, 0666) = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fchmod(3, 0644)                         = 0
open("config", O_RDONLY|O_LARGEFILE)    = 4
open("config", O_RDONLY|O_LARGEFILE)    = 5
fstat(5, {st_mode=S_IFREG|0644, st_size=36, ...}) = 0
read(5, "[core]\n\trepositoryformatversion "..., 1024) = 36
writev(1, [{iov_base="iter=1 git-like read(fd2): n=36 "..., iov_len=42}, {iov_base="\n", iov_len=1}], 2iter=1 git-like read(fd2): n=36 st_size=36
) = 43
close(5)                                = 0
fstat(4, {st_mode=S_IFREG|0644, st_size=36, ...}) = 0
mmap(NULL, 36, PROT_READ, MAP_PRIVATE, 4, 0) = 0x7f520c347000
close(4)                                = 0
write(3, "[core]\n", 7)                 = 7
write(3, "\tbare = false\n", 14)        = 14
write(3, "[core]\n\trepositoryformatversion "..., 36) = 36
writev(1, [{iov_base="iter=1 git-like mmap-copy write:"..., iov_len=37}, {iov_base="\n", iov_len=1}], 2iter=1 git-like mmap-copy write: n=36
) = 38
munmap(0x7f520c347000, 36)              = 0
close(3)                                = 0
writev(1, [{iov_base="\n", iov_len=1}], 1
) = 1
writev(1, [{iov_base="=== iter 2 write len=53", iov_len=23}, {iov_base=" ===\n", iov_len=5}], 2=== iter 2 write len=53 ===
) = 28
unlink("config.lock")                   = 0
open("config.lock", O_RDWR|O_CREAT|O_EXCL|O_LARGEFILE|O_CLOEXEC, 0666) = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
fchmod(3, 0644)                         = 0
write(3, "[core]\n\trepositoryformatversion "..., 53) = 53
close(3)                                = 0
rename("config.lock", "config")         = 0
open("config", O_RDONLY|O_LARGEFILE)    = 3
read(3, 0x7fffacf4b590, 1024)           = -1 EIO (I/O error)
writev(2, [{iov_base="\nITER 2: read(config) failed: er"..., iov_len=50}, {iov_base=NULL, iov_len=0}], 2
ITER 2: read(config) failed: errno=5 (I/O error)
) = 50
close(3)                                = 0
exit_group(2)                           = ?
+++ exited with 2 +++