| Message ID | 1486045589-8074-1-git-send-email-den@openvz.org |
|---|---|
| State | New |
| Headers | show |
On 02/02/2017 06:26, Denis V. Lunev wrote: > From: Anton Nefedov <anton.nefedov@virtuozzo.com> > > Socket backend read handler should normally perform a disconnect, however > the read handler may not get a chance to run if the frontend is not ready > (qemu_chr_be_can_write() == 0). > > This means that in virtio-serial frontend case if > - the host has disconnected (giving EPIPE on socket write) > - and the guest has disconnected (-> frontend not ready -> backend > will not read) > - and there is still data (frontend->backend) to flush (has to be a really > tricky timing but nevertheless, we have observed the case in production) > > This results in virtio-serial trying to flush this data continiously forming > a busy loop. > > Solution: react on write error in the socket write handler. > errno is not reliable after qio_channel_writev_full(), so we may not get > the exact EPIPE, so disconnect on any error but QIO_CHANNEL_ERR_BLOCK which > io_channel_send_full() converts to errno EAGAIN. > We must not disconnect right away though, there still may be data to read > (see 4bf1cb0). > > Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com> > Signed-off-by: Denis V. Lunev <den@openvz.org> > CC: Paolo Bonzini <pbonzini@redhat.com> > CC: Daniel P. Berrange <berrange@redhat.com> > CC: Marc-André Lureau <marcandre.lureau@redhat.com> > --- > Changes from v2: > - fixed prototype of tcp_chr_disconnect > > Changes from v1: > - we do not rely on EPIPE anynore. Socket should be closed on all errors > except EAGAIN > > chardev/char-socket.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/chardev/char-socket.c b/chardev/char-socket.c > index 4068dc5..865c527 100644 > --- a/chardev/char-socket.c > +++ b/chardev/char-socket.c > @@ -97,6 +97,9 @@ static gboolean tcp_chr_accept(QIOChannel *chan, > GIOCondition cond, > void *opaque); > > +static int tcp_chr_read_poll(void *opaque); > +static void tcp_chr_disconnect(Chardev *chr); > + > /* Called with chr_write_lock held. */ > static int tcp_chr_write(Chardev *chr, const uint8_t *buf, int len) > { > @@ -114,6 +117,13 @@ static int tcp_chr_write(Chardev *chr, const uint8_t *buf, int len) > s->write_msgfds_num = 0; > } > > + if (ret < 0 && errno != EAGAIN) { > + if (tcp_chr_read_poll(chr) <= 0) { > + tcp_chr_disconnect(chr); > + return len; > + } /* else let the read handler finish it properly */ > + } > + > return ret; > } else { > /* XXX: indicate an error ? */ > Queued, thanks. Paolo
diff --git a/chardev/char-socket.c b/chardev/char-socket.c index 4068dc5..865c527 100644 --- a/chardev/char-socket.c +++ b/chardev/char-socket.c @@ -97,6 +97,9 @@ static gboolean tcp_chr_accept(QIOChannel *chan, GIOCondition cond, void *opaque); +static int tcp_chr_read_poll(void *opaque); +static void tcp_chr_disconnect(Chardev *chr); + /* Called with chr_write_lock held. */ static int tcp_chr_write(Chardev *chr, const uint8_t *buf, int len) { @@ -114,6 +117,13 @@ static int tcp_chr_write(Chardev *chr, const uint8_t *buf, int len) s->write_msgfds_num = 0; } + if (ret < 0 && errno != EAGAIN) { + if (tcp_chr_read_poll(chr) <= 0) { + tcp_chr_disconnect(chr); + return len; + } /* else let the read handler finish it properly */ + } + return ret; } else { /* XXX: indicate an error ? */