On Fri, Feb 22, 2019 at 10:06 AM Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: > > On Fri, 2019-02-22 at 09:46 -0500, Olga Kornievskaia wrote: > > On Fri, Feb 22, 2019 at 8:45 AM Trond Myklebust < > > trondmy@xxxxxxxxxxxxxxx> wrote: > > > On Fri, 2019-02-22 at 07:12 -0500, Dave Wysochanski wrote: > > > > Hi Olga, > > > > > > > > Do you have a reproducer for this? A number of months ago I did > > > > a > > > > significant amount of testing with half-closed connections, after > > > > we > > > > had reports of connections stuck in FIN_WAIT2 in some older > > > > kernels. > > > > What I found was with kernels that had the tcp keepalives (commit > > > > 7f260e8575bf53b93b77978c1e39f8e67612759c), I could only reproduce > > > > a > > > > hang of a few minutes, after which time the tcp keepalive code > > > > would > > > > reset the connection. > > > > > > > > That said it was a while ago and something subtle may have > > > > changed. > > > > Also I'm not not sure if your header implies an indefinite hang > > > > or > > > > just > > > > a few minutes. > > > > > > > > Thanks. > > > > > > > > > > > > On Wed, 2019-02-20 at 09:56 -0500, Olga Kornievskaia wrote: > > > > > From: Olga Kornievskaia <kolga@xxxxxxxxxx> > > > > > > > > > > When server replies with an ACK to client's FIN/ACK, client > > > > > ends > > > > > up stuck in a TCP_FIN_WAIT2 state and client's mount hangs. > > > > > Instead, make sure to close and reset client's socket and > > > > > transport > > > > > when transitioned into that state. > > > > Hi Trond, > > > > > So, please do note that we do not want to ignore the FIN_WAIT2 > > > state > > > > But we do ignore the FIN_WAIT2 state. > > We do not. We wait for the server to send a FIN, which is precisely the > reason for which FIN_WAIT2 exists. > > > > > > because it implies that the server has not closed the socket on its > > > side. > > > > That's correct. > > > > > That again means that we cannot re-establish a connection using > > > the same source IP+port to the server, which is problematic for > > > protocols such as NFSv3 which rely on standard duplicate reply > > > cache > > > for correct replay semantics. > > > > that's exactly what's happening that a client is unable to establish > > a > > new connection to the server. With the patch, the client does an RST > > and it re-uses the port and all is well for NFSv3. > > RST is not guaranteed to be delivered to the recipient. That's why the > TCP protocol defines FIN: it is a guaranteed to be delivered because it > is ACKed. > > > > This is why we don't just set the TCP_LINGER2 socket option and > > > call > > > sock_release(). The choice to try to wait it out is deliberate > > > because > > > the alternative is that we end up with busy-waiting re-connection > > > attempts. > > > > Why would it busy-wait? In my testing, RST happens and new connection > > is established? > > Only if the server has dropped the connection without notifying the > client. Yes the server dropped the connection without notifying the client (or perhaps something in the middle did it as an attack). Again, I raise this concern for the sake of dealing with this as an attack. I have no intentions of catering to broken servers. If this is not a possible attack, then we don't have to deal with it.
