From b0a335e351103bf92f3f9d0bd5759311be8156ac Mon Sep 17 00:00:00 2001 From: Anton Nefedov Date: Thu, 2 Feb 2017 17:26:29 +0300 Subject: [PATCH] qemu-char: socket backend: disconnect on write error MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Denis V. Lunev CC: Paolo Bonzini CC: Daniel P. Berrange CC: Marc-André Lureau Message-Id: <1486045589-8074-1-git-send-email-den@openvz.org> Signed-off-by: Paolo Bonzini --- chardev/char-socket.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/chardev/char-socket.c b/chardev/char-socket.c index 4068dc5e52..865c52762e 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 ? */