c478f4c43c
I've got a case where usbredir_write manages to call back into itself via spice; this patch causes the recursion to fail (0 bytes) the write; this seems to avoid the deadlock I was previously seeing. I can't say I fully understand the interaction of usbredir and spice; but there are a few similar guards in spice and usbredir to catch other cases especially onces also related to spice_server_char_device_wakeup This case seems to be triggered by repeated migration+repeated reconnection of the viewer; but my debugging suggests the migration finished before this hits. The backtrace of the hang looks like: reds_handle_ticket reds_handle_other_links reds_channel_do_link red_channel_connect spicevmc_connect usbredir_create_parser usbredirparser_do_write usbredir_write qemu_chr_fe_write qemu_chr_write qemu_chr_write_buffer spice_chr_write spice_server_char_device_wakeup red_char_device_wakeup red_char_device_write_to_device vmc_write usbredirparser_do_write usbredir_write qemu_chr_fe_write qemu_chr_write qemu_chr_write_buffer qemu_mutex_lock_impl and we fail as we lang through qemu_chr_write_buffer's lock twice. Bug: https://bugzilla.redhat.com/show_bug.cgi?id=1752320 Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Message-Id: <20191218113012.13331-1-dgilbert@redhat.com> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>