On 12.01.2012 11:13, Daniel P. Berrange wrote:
On Thu, Jan 12, 2012 at 09:54:15AM +0100, Michal Privoznik wrote:
If client stream does not have any data to sink and neither received EOF, a dummy packet is sent to the daemon signalising client is ready to sink some data. However, after we added event loop to client a race may occur:
Thread 1 calls virNetClientStreamRecvPacket and since no data are cached nor stream has EOF, it decides to send dummy packet to server which will sent some data in turn. However, during this decision and actual message exchange with server -
Thread 2 receives last stream data from server. Therefore an EOF is set on stream and if there is a call waiting (which is not yet) it is woken up. However, Thread 1 haven't sent anything so far, so there is no call to be woken up. So this thread sent dummy packet to daemon, which ignores that as no stream is associated with such packet and therefore no reply will ever come.
This race causes client to hang indefinitely. --- diff to v1: -moved client locking one level higher -checking for stream EOF one level higher too
src/rpc/virnetclient.c | 51 +++++++++++++++++++++++++++++++++++++----- src/rpc/virnetclient.h | 3 ++ src/rpc/virnetclientstream.c | 7 +++++- src/rpc/virnetclientstream.h | 2 + 4 files changed, 56 insertions(+), 7 deletions(-)
ACK
Daniel
Thanks, pushed. Michal