On 18/10/2016 16:01, Daniel P. Berrange wrote: >> > >> > I already use error_report's in places in migration threads of various >> > types; I'm not sure if that's a problem. > Unless those places are protected by the big qemu lock, that sounds > not good. error_report calls into error_vprintf which checks the > 'cur_mon' global "Monitor" pointer. This variable is updated at > runtime - eg in qmp_human_monitor_command(), monitor_qmp_read(), > monitor_read(), etc. So if migration threads outside the BQL are > calling error_report() that could well cause problems. If you > are lucky messages will merely end up going to stderr instead of > the monitor, but in worst case I wouldn't be surprised if there > is a crash possibility in some race conditions.
Writes to chardevs *are* thread-safe (assuming qio_channel_create_watch is thread-safe; it seems to be). Only reads aren't, in the sense that they require an event loop so they use that event loop for serialization. Paolo
