On Wed, Jul 21, 2021 at 10:55:00AM +0100, Dr. David Alan Gilbert wrote: > * Peter Xu (pet...@redhat.com) wrote: > > We have a logic in await_return_path_close_on_source() that we will > > explicitly > > shutdown the socket when migration encounters errors. However it could be > > racy > > because from_dst_file could have been reset right after checking it but > > before > > passing it to qemu_file_shutdown() by the rp_thread. > > > > Fix it by shutdown() on the src file instead. Since they must be a pair of > > qemu files, shutdown on either of them will work the same. > > > > Since at it, drop the check for from_dst_file directly, which makes the > > behavior even more predictable. > > So while the existing code maybe racy, I'm not sure that this change > keeps the semantics; the channel may well have dup()'d the fd's for the > two directions, and I'm not convinced that a shutdown() on one will > necessarily impact the other; and if the shutdown doesn't happen the > rp_thread might not exit, and we might block on the koin.
My understanding is that 'shutdown' operation affects the state of the socket connection. An FD is merely the way a socket is exposed to userspace. Thus if you have multiple FDs all pointing to the same underlying socket (thanks to dup()), then I expect that the effects of 'shutdown' will apply equally to all of the FD copies. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
