CONFIG_NET_TCP_WRITE_BUFFERS=y lead to deadlock

[pkarashchenko]

Recently I've been testing FTPD operation on custom SAME70 based board with FileZilla FTP client. I had CONFIG_NET_TCP_WRITE_BUFFERS=y.

I have a folder with 2 files that I try to upload from laptop to device. Upload of a folder fails.

FileZilla starts 2 FTP sessions in parallel one for each file upload so 2 instances of ftpd_worker are started. The situation happens in 80% of my tests. The FTP client send "STOR" command for both files and by adding extra logs I see that both threads reach ftpd.c:1908 code ret = ftpd_response(session->cmd.sd, session->txtimeout, g_respfmt1, 150, ' ', "Opening data connection"); at the same time so send is called concurrently.

The logs before ftpd_response call are printed, but there are no logs after ftpd_response call. NSH "ps" shows that both threads are "waiting for semaphore", but most probably loop somewhere inside the psock_tcp_send trying to allocate iob.

Setting CONFIG_NET_TCP_WRITE_BUFFERS=n solves the issue and FTP server operates as expected.