fork without exec 子进程一直卡死在bthread::futex_wait_private

[mike8848]

Describe the bug BUG描述
fork without exec , 父进程中成功执行过rpc调用， 然后fork一个子进程， 在子进程中执行rcp调用会一直卡死在bthread::futex_wait_private。相关堆栈如下：

#0 0x00007fb792d3c52d in syscall () from /lib64/libc.so.6
#1 0x00007fb795761fe4 in bthread::futex_wait_private (timeout=0x0, expected=0, addr1=0x7ffc42c1e3a0) at /home/brpc/src/bthread/sys_futex.h:40
#2 bthread::wait_pthread (pw=..., abstime=, abstime@entry=0x0) at /home/brpc/src/bthread/butex.cpp:150
#3 0x00007fb79576288e in bthread::butex_wait_from_pthread (prepend=, abstime=0x0, expected_value=1, b=0x3453f60, g=) at /home/brpc/src/bthread/butex.cpp:634
#4 bthread::butex_wait (arg=arg@entry=0x3453f60, expected_value=expected_value@entry=1, abstime=abstime@entry=0x0, prepend=prepend@entry=false) at /home/brpc/src/bthread/butex.cpp:667
#5 0x00007fb79576c93b in bthread_id_join (id=...) at /home/brpc/src/bthread/id.cpp:530
#6 0x00007fb7955ab225 in brpc::Join (id=..., id@entry=...) at /home/brpc/src/brpc/controller.cpp:581
#7 0x00007fb7955a62db in brpc::Channel::CallMethod (this=0x7fb795d93360 <hsmdClient+128>, method=0x33fecb8, controller_base=0x7ffc42c1e610, request=0x7ffc42c1e5a0, response=0x7ffc42c1e5c0, done=0x0) at /home/brpc/src/brpc/channel.cpp:589
#8 0x00007fb795528dd8 in master::pb::MasterService_Stub::QueryLeader (this=0x7ffc42c1e580, controller=0x7ffc42c1e610, request=0x7ffc42c1e5a0, response=0x7ffc42c1e5c0, done=0x0) at /home/hsm/libhsmd/../common/pb/master.pb.cc:25807
#9 0x00007fb7954c1187 in common::RpcClientMaster::QueryLeader (this=0x7ffc42c1e9d0, failLeaderEndpoint="", leader_name="master2", leader_endpoint="10.16.16.203:8002") at /home/hsm/libhsmd/../common/rpcclient/rpcclient_master.cpp:169

To Reproduce 复现

Status CallRpc()
{
    brpc::ChannelOptions options;
    options.use_rdma = use_rdma;
    options.protocol = "baidu_std";
    options.connection_type = "single";  // // Possible values: "single", "pooled", "short".
    options.timeout_ms = 10000;          /*milliseconds*/
    options.max_retry = 3;               // Default: 3
    if (channel_->Init(server_addr.c_str(), port, &options) != 0)
    {
        LOG(ERROR) << "Fail to initialize channel " << server_addr + ":" << port;
        return false;
    }

    master::pb::QueryLeaderRequest request;
    master::pb::QueryLeaderResponse response;
    request.set_failleaderendpoint(failLeaderEndpoint); 

    master::pb::MasterService_Stub stub(channel_);
    brpc::Controller cntl;
    stub.QueryLeader(&cntl, &request, &response, NULL);
    leader_name = response.leader_name();
    leader_endpoint = response.leader_endpoint();
    Status status = CheckResult("RpcClientMaster::QueryLeader", &cntl, response.status().code(), response.status().message());
    return status;
}


int TestBrpcForkWithoutExec()
{
    printf("main  pid=%d\r\n",getpid());
    
    //如果在父进程中调用过CallRpc()， 则在子进程中就会 卡死. 如果父进程中没有调用过CallRpc(), 则子进程中均正常执行
    CallRpc()；

    for(int i=0;i<2;i++)
    {
        pid_t p = fork();
        if (p == 0)  
        { //子进程中执行
            printf("%d child pid=%d\r\n",i, getpid());
            //会一直在等待在 bthread::futex_wait_private          
            if (!CallRpc())
            {
                printf("%d child client.Init failed\r\n",i);
                return 0;
            }
            else
            {
                printf("%d child client.Init success\r\n",i);
                return -1;
            }
            
        }
    }

    return 0;
}

Expected behavior
fork()子进程后， 能提供接口重新初始化brpc环境， 以便子进程中仍能正常工作。
既然有GlobalInitializeOrDie()这个函数，为什么没有GlobalClear() 清理brpc环境呢？
尝试过修改子进程中channel_->Init()之前修改 register_extensions_once = PTHREAD_ONCE_INIT; 但是报错，估计不行。
官方有没有更好的办法？

Versions
OS: CentOS Linux 8
Compiler: gcc 8.5
brpc: 1.13
protobuf: 3.5

Additional context/screenshots

[zhoukangsheng]

This is not a bug and it is a very classic deadlock problem caused by fork.The lock you added in the parent process is copied to the child process, but there is no corresponding thread in the child process to unlock it, so it is stuck there.

Try forking and then exec!