• VPP version: v18.01-rc0~476-g6f8273a

• After the server's first call to ssize_t read(int fd, void *buf, size_t count) has returned all expected data sent by a client,
  the same subsequent read() call loops endlessly in the VCL-LDPRELOAD library.

svm_fifo_dequeue_internal() returns -2 at svm_fifo.c:626:

625      if (PREDICT_FALSE (cursize == 0))
626        return -2;          /* nothing in the fifo */

Therefore, the following do/while from within vppcom_session_read_internal() in src/vcl/vppcom.c loops endlessly (is_nonblocking == 0, n_read == -2):

2730  do
2731    {
2732      if (peek)
2733    n_read = svm_fifo_peek (rx_fifo, 0, n, buf);
2734      else
2735    n_read = svm_fifo_dequeue_nowait (rx_fifo, n, buf);
2736    }
2737  while (!is_nonblocking && (n_read <= 0));

• Stack trace:

#0  svm_fifo_dequeue_internal (f=0x200f07040, max_bytes=1024, copy_here=0x7fffffffd6a0 "Hallo Dude!") at /home/palmar/dev/vpp/build-data/../src/svm/svm_fifo.c:626
#1  0x00007ffff7b5cd35 in svm_fifo_dequeue_nowait_ma (f=0x200f07040, max_bytes=1024, copy_here=0x7fffffffd6a0 "Hallo Dude!") at /home/palmar/dev/vpp/build-data/../src/svm/svm_fifo.c:673
#2  0x00007ffff7b5cdb6 in svm_fifo_dequeue_nowait (f=0x200f07040, max_bytes=1024, copy_here=0x7fffffffd6a0 "Hallo Dude!") at /home/palmar/dev/vpp/build-data/../src/svm/svm_fifo.c:693
#3  0x00007ffff799fcd4 in vppcom_session_read_internal (session_index=1, buf=0x7fffffffd6a0, n=1024, peek=0 '\000') at /home/palmar/dev/vpp/build-data/../src/vcl/vppcom.c:2735
#4  0x00007ffff799ff8b in vppcom_session_read (session_index=1, buf=0x7fffffffd6a0, n=1024) at /home/palmar/dev/vpp/build-data/../src/vcl/vppcom.c:2793
#5  0x00007ffff7980c34 in vcom_socket_read (__fd=8, __buf=0x7fffffffd6a0, __nbytes=1024) at /home/palmar/dev/vpp/build-data/../src/vcl/vcom_socket.c:472
#6  0x00007ffff7977b39 in vcom_read (__fd=8, __buf=0x7fffffffd6a0, __nbytes=1024) at /home/palmar/dev/vpp/build-data/../src/vcl/vcom.c:228
#7  0x00007ffff7977bad in read (__fd=8, __buf=0x7fffffffd6a0, __nbytes=1024) at /home/palmar/dev/vpp/build-data/../src/vcl/vcom.c:246
(...)