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

[Vitaly Kuznetsov <vkuznets@redhat.com>]

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