On Tue, Oct 12, 2021 at 02:41:39PM +0200, Michal Privoznik wrote: > This commit is related to 5de203f879 which I pushed a few days > ago. While that commit prioritized closing clients socket over > the rest of I/O process, this one goes one step further and > temporarily suspends processing new connection requests. > > A brief recapitulation of the problem: > > 1) assume that libvirt is at the top of RLIMIT_NOFILE (that is no > new FDs can be opened). > > 2) we have a client trying to connect to a UNIX/TCP socket > > Because of 2) our event loop sees POLLIN on the socket and thus > calls virNetServerServiceAccept(). But since no new FDs can be > opened (because of 1)) the request is not handled and we will get > the same event on next iteration. The poll() will exit > immediately because there is an event on the socket. Thus we end > up in an endless loop. > > To break the loop and stop burning CPU cycles we can stop > listening for events on the socket and set up a timer tho enable > listening again after some time (I chose 5 seconds because of no > obvious reason). > > There's another area where we play with temporarily suspending > accept() of new clients - when a client disconnects and we check > max_clients against number of current clients. Problem here is > that max_clients can be orders of magnitude larger than > RLIMIT_NOFILE but more importantly, what this code considers > client disconnect is not equal to closing client's FD. > A client disconnecting means that the corresponding client > structure is removed from the internal list of clients. Closing > of the client's FD is done from event loop - asynchronously. > > To avoid this part stepping on the toes of my fix, let's make the > code NOP if socket timer (as described above) is active. > > Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx> > --- > src/libvirt_remote.syms | 1 + > src/rpc/virnetserver.c | 9 ++++++ > src/rpc/virnetserverservice.c | 53 ++++++++++++++++++++++++++++++++++- > src/rpc/virnetserverservice.h | 2 ++ > src/rpc/virnetsocket.c | 15 ++++++++++ > 5 files changed, 79 insertions(+), 1 deletion(-) Reviewed-by: Daniel P. Berrangé <berrange@xxxxxxxxxx> 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 :|
