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

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Date:	Wed, 19 Nov 2014 12:15:21 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH] tools: hv: ignore ENOBUFS in the KVP daemon

> -----Original Message-----
> From: Vitaly Kuznetsov
> Sent: Wednesday, November 19, 2014 18:50 PM
> To: Dexuan Cui
> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; driverdev-
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> jasowang@...hat.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().

-- Dexuan
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