Bug 1570502

Description of problem:
Using alsa->pulse I have triggered something that looks like BZ #534130 again.

An application pjsua from https://github.com/pjsip/pjproject compiled to use alsa hangs when closing the capture device alsa->pulse in poll() inside snd1_pcm_wait_nocheck().

pjsua used to work under Fedora 27. The same issue occurs if using the binary compiled on F27 and recompiling under Fedora 28.


Version-Release number of selected component (if applicable):
alsa-lib-1.1.6-2.fc28.x86_64
alsa-plugins-pulseaudio-1.1.6-3.fc28.x86_64


How reproducible:
Always

Steps to Reproduce:
1. Build pjsua on F27/F28 with alsa sound driver
2. Run pjsua, make a call, and try to exit gracefully
3.

Actual results:
Hang 

(gdb) bt
#0  0x00007ff0f0cba929 in poll () at /lib64/libc.so.6
#1  0x00007ff0f164e293 in snd1_pcm_wait_nocheck () at /lib64/libasound.so.2
#2  0x00007ff0f1698274 in snd_pcm_ioplug_drain () at /lib64/libasound.so.2
#3  0x00007ff0f457a868 in ca_thread_func (arg=0x15236a8) at ../src/pjmedia-audiodev/alsa_dev.c:596
#4  0x00007ff0f2c1dca9 in thread_main (param=0x15367c0) at ../src/pj/os_core_unix.c:541
#5  0x00007ff0f1902564 in start_thread () at /lib64/libpthread.so.0
#6  0x00007ff0f0cc531f in clone () at /lib64/libc.so.6


Expected results:
App exits gracefully


Additional info:
Works fine with native Alsa devices, i.e., blacklist device from pulse in pavucontrol

At the hanging point the app is trying to close a capture device; the thread function that blocks looks like

static int ca_thread_func (void *arg)
{
    struct alsa_stream* stream = (struct alsa_stream*) arg;
    snd_pcm_t* pcm             = stream->ca_pcm;
    int size                   = stream->ca_buf_size;
    snd_pcm_uframes_t nframes  = stream->ca_frames;
    void* user_data            = stream->user_data;
    char* buf                  = stream->ca_buf;
    pj_timestamp tstamp;
    int result;
    struct sched_param param;
    pthread_t* thid;

    thid = (pthread_t*) pj_thread_get_os_handle (pj_thread_this());
    param.sched_priority = sched_get_priority_max (SCHED_RR);
    PJ_LOG (5,(THIS_FILE, "ca_thread_func(%u): Set thread priority "
                          "for audio capture thread.",
                          (unsigned)syscall(SYS_gettid)));
    result = pthread_setschedparam (*thid, SCHED_RR, &param);
    if (result) {
        if (result == EPERM)
            PJ_LOG (5,(THIS_FILE, "Unable to increase thread priority, "
                                  "root access needed."));
        else
            PJ_LOG (5,(THIS_FILE, "Unable to increase thread priority, "
                                  "error: %d",
                                  result));
    }

    pj_bzero (buf, size);
    tstamp.u64 = 0;

    TRACE_((THIS_FILE, "ca_thread_func(%u): Started",
            (unsigned)syscall(SYS_gettid)));

    snd_pcm_prepare (pcm);


    TRACE_((THIS_FILE, "ca_thread_func(%u): Started",
            (unsigned)syscall(SYS_gettid)));

    snd_pcm_prepare (pcm);

    while (!stream->quit) {
        pjmedia_frame frame;

        pj_bzero (buf, size);
        result = snd_pcm_readi (pcm, buf, nframes);
        if (result == -EPIPE) {
            PJ_LOG (4,(THIS_FILE, "ca_thread_func: overrun!"));
            snd_pcm_prepare (pcm);
            continue;
        } else if (result < 0) {
            PJ_LOG (4,(THIS_FILE, "ca_thread_func: error reading data!"));
        }
        if (stream->quit)
            break;

        frame.type = PJMEDIA_FRAME_TYPE_AUDIO;
        frame.buf = (void*) buf;
        frame.size = size;
        frame.timestamp.u64 = tstamp.u64;
        frame.bit_info = 0;

        result = stream->ca_cb (user_data, &frame);
        if (result != PJ_SUCCESS || stream->quit)
            break;

        tstamp.u64 += nframes;
    }
    snd_pcm_drain (pcm);
    TRACE_((THIS_FILE, "ca_thread_func: Stopped"));

    return PJ_SUCCESS;
}

The hang seems to be in snd_pcm_drain(pcm)