RE: [PATCH] tools: hv: ignore ENOBUFS in the KVP daemon

[Dexuan Cui <decui@microsoft.com>]

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
> Sent: Wednesday, November 19, 2014 20:41 PM
> To: Dexuan Cui
> Cc: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org; driverdev-
> devel@linuxdriverproject.org; olaf@aepfle.de; apw@canonical.com;
> jasowang@redhat.com; Haiyang Zhang
> Subject: Re: [PATCH] tools: hv: ignore ENOBUFS in the KVP daemon
> 
> Dexuan Cui <decui@microsoft.com> writes:
> 
> >> -----Original Message-----
> >> From: Vitaly Kuznetsov
> >> Sent: Wednesday, November 19, 2014 18:50 PM
> >> To: Dexuan Cui
> >> Cc: gregkh@linuxfoundation.org; linux-kernel@vger.kernel.org;
> driverdev-
> >> devel@linuxdriverproject.org; olaf@aepfle.de; apw@canonical.com;
> >> jasowang@redhat.com; Haiyang Zhang
> >> Subject: Re: [PATCH] tools: hv: ignore ENOBUFS in the KVP daemon
> >>
> >> Dexuan Cui  writes:
> >>
> >> > Under high memory pressure and very high KVP R/W test pressure,
> the netlink
> >> > recvfrom() may transiently return ENOBUFS to the daemon -- we found
> this
> >> > during a 2-week stress test.
> >> >
> >> > We'd better not terminate the daemon on this failure, because a
> typical KVP
> >> > user can re-try the R/W and hopefully it will succeed next time.
> >> >
> >> > diff --git a/tools/hv/hv_kvp_daemon.c b/tools/hv/hv_kvp_daemon.c
> >> > index 22b0764..9f4b303 100644
> >> > --- a/tools/hv/hv_kvp_daemon.c
> >> > +++ b/tools/hv/hv_kvp_daemon.c
> >> > @@ -1559,8 +1559,15 @@ int main(int argc, char *argv[])
> >> >  				addr_p, &addr_l);
> >> >
> >> >  		if (len < 0) {
> >> > +			int saved_errno = errno;
> >> >  			syslog(LOG_ERR, "recvfrom failed; pid:%u
> error:%d %s",
> >> >  					addr.nl_pid, errno, strerror(errno));
> >> > +
> >> > +			if (saved_errno == ENOBUFS) {
> >>
> >> is it possible to meet EAGAIN (or EWOULDBLOCK) here as well? I'd
> suggest
> >> we ignore these as well in such case. Ignoring ENOMEM here is doubtful,
> >> I think. But possible.
> >>
> >>   Vitaly
> >
> > I don't think EAGAIN is possible  because "man recvfrom" says
> >    "If  no messages are available at the socket, the receive calls wait for a
> >      message to arrive, unless the socket is nonblocking (see fcntl(2)), in
> which
> >      case the value -1 is returned and  the  external variable  errno is set to
> >     EAGAIN or EWOULDBLOCK".
> >
> > The same man page mention ENOMEM for recvmsg(), but not recvfrom().
> 
> Ah, sorry, I though your patch patches the other place: call to
> netlink_send() which does sendmsg() (and my
> EAGAIN/EWOULDBLOCK/ENOMEM
> comment was about it). It could also make sense to patch them both as I
> think it is possible to hit these as well.
> 
> > -- Dexuan
> --
>   Vitaly

OK, I can add this new check:
(I'll send out the v2 tomorrow in case  people have new comments)

--- a/tools/hv/hv_kvp_daemon.c
+++ b/tools/hv/hv_kvp_daemon.c
@@ -1770,8 +1770,15 @@ kvp_done:

                len = netlink_send(fd, incoming_cn_msg);
                if (len < 0) {
+                       int saved_errno = errno;
                        syslog(LOG_ERR, "net_link send failed; error: %d %s", errno,
                                        strerror(errno));
+
+                       if (saved_errno == ENOMEM || saved_errno == EAGAIN) {
+                               syslog(LOG_ERR, "send error: ignored");
+                               continue;
+                       }
+
                        exit(EXIT_FAILURE);
                }
        }

Thanks,
-- Dexuan