Segfault with error 4 in pthread_create

Question

I consistently receive following segfault with error 4 (which afaik is null pointer dereference by checking on https://rgeissert.blogspot.com/p/segmentation-fault-error.html ):

Aug  6 11:42:54 mypc kernel: [28532305.723536] myapp-new[14784]: segfault at 18 ip 00007f642c6c5d44 sp 00007ffc6a937700 error 4 in libpthread-2.23.so[7f642c6bc000+18000]

Code is following:

void* request(void* p){
    // ... code
}

void Daemon::run(){

    pthread_attr_t attr; 
    pthread_attr_init(&attr); 
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

    LOG(INFO) << "daemon running...";

    int sockfd = serverSocket.getSocket();

    struct pollfd fds[1]; 
    fds[0].fd = sockfd; 
    fds[0].events = POLLIN | POLLPRI;

    pthread_t threads[1];

    while (!shutdown_daemon) {
        int currNrThreads = activeThreads;
        int i = 0;
        for (; activeThreads > nrThreads; i++) {
            usleep(4000);
        }
        if (i != 0) {
            LOG(INFO) << "too many threads, slept for " << i * 4 << "ms (" << currNrThreads
                      << " threads, now " << activeThreads << ")";
        }

        // wait until there is data to read on the listen socket
        //
        int retVal = poll(fds, 1, 2000);
        if (retVal == -1) {
            LOG(WARNING) << "error in poll: " << strerror(errno);
        }

        if (retVal <= 0) {
            continue;
        }

        // open a socket to communicate with and read the header
        //
        struct sockaddr_storage clientAddr;
        unsigned int clientLen = sizeof(clientAddr);
        int connectionID = accept(sockfd, (struct sockaddr*)&clientAddr, &clientLen);
        if (connectionID == -1) {
            LOG(WARNING) << "accept return -1, error: " << strerror(errno);
            continue;
        }

        // pack the payload into buffer
        auto buf = new size_t[2];
        buf[0] = (size_t)this;
        buf[1] = (size_t)connectionID;

        int ret = pthread_create(&threads[0], &attr, &request, (void*)buf);
        if (ret != 0) {
            LOG(ERROR) << "could not start pthread, ret: '" << ret << "'";
            delete[] buf;
            continue;
        }
        // Atomic increment
        ++activeThreads; 
    }

    LOG(INFO) << "term signal received, waiting child processess to finish";

    while (activeThreads > 0) {
        LOG(INFO) << "waiting for child processes to finish...";
        sleep(1); }

    LOG(INFO) << "all child processes are finished";
}

with following backtrace:

(gdb) bt
#0  __pthread_create_2_1 (newthread=<optimized out>, attr=<optimized out>, start_routine=<optimized out>, arg=<optimized out>) at pthread_create.c:713
#1  0x00000000004621fb in Daemon::run (this=0x7ffe1715d260) at src/daemon/daemon.cpp:992
#2  0x0000000000443842 in main (argc=4, argv=0x7ffe1715d6f8) at src/myapp.cpp:991
(gdb) bt full
#0  __pthread_create_2_1 (newthread=<optimized out>, attr=<optimized out>, start_routine=<optimized out>, arg=<optimized out>) at pthread_create.c:713
        stackaddr = <optimized out>
        iattr = <optimized out>
        default_attr = {schedparam = {__sched_priority = 0}, schedpolicy = 0, flags = -1456592096, guardsize = 16,
          stackaddr = 0x409d50 <_GLOBAL__sub_I__ZN4YAML5RegExC2Ev+16>, stacksize = 140729285727984, cpuset = 0x0, cpusetsize = 0}
        free_cpuset = <optimized out>
        pd = 0x7fb373fff700
        retval = <optimized out>
        self = <optimized out>
        thread_ran = true
        __PRETTY_FUNCTION__ = "__pthread_create_2_1"
#1  0x00000000004621fb in Daemon::run (this=0x7ffe1715d260) at src/daemon/daemon.cpp:992
        currNrThreads = -1447528544
        i = 8
        retVal = 0
        clientAddr = {ss_family = 2,
          __ss_padding = "\336L\177\000\000\001", '\000' <repeats 24 times>, "\260\315\025\027\376\177\000\000\006\000\000\000\000\000\000\000daemon\000\000\b\317\025\027\376\177\000\000\320\315\025\027\376\177\000\000\n\000\000\000\000\000\000\000BackupLock\000\027\376\177\000\000\000\316\025\027\376\177\000\000!\303@\000\000\000\000\000\274\204O\000\000\000\000", __ss_align = 140729285725960}
        buf = 0x7fb300000000
        clientLen = 32691
        connectionID = 3
        attr = {__size = "\000\000\000\000\000\000\000\000\001\000\000\000\000\000\000\000\000\020", '\000' <repeats 37 times>, __align = 0}
        __PRETTY_FUNCTION__ = "void Daemon::run()"
        sockfd = 16
        fds = {{fd = 3, events = 3, revents = 1}}
        threads = {140408722028288}

How is it possible? I would understand some out of memory error, but where can error 4 happen in this code ( Ubuntu 16.04, glibc 2.2.3 )

We also suspected hardware issues so replaced all RAM on this machine but issue persisted.

Update on this: after moving software to another machine (with glibc 2.26) crashes completely stopped (under same load).

Answer 1

First of all,

I would try to replace the following:

// pack the payload into buffer
auto buf = new size_t[2];
buf[0] = (size_t)this;
buf[1] = (size_t)connectionID;

With a nice struct, like:

struct thread_param
{
  Daemon* deamon;
  int connectionID;
}

maybe I'm just paranoid, but I wouldn't use auto declaration in such as case where I'll be needed to cast it later...

Second

it can be so many reasons to crush, and you didn't gave the whole information.

Does your program crash at:

1. The first iteration?
2. The second iteration?
3. The 1000th iterfation?

For each case it may caused by other reason:

1. You are using an uninitialized pointer.
2. You are using a deleted pointer.
3. You have a memory leak and it cause some memory allocation to failed. For example I odn't see you're deleting buf in case the pthread_create has succeeded (I guess it should be in the request function, and you didn't check if allocation had been succeded...)