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

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Date:	Wed, 19 Nov 2014 14:05:12 +0100
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Dexuan Cui <decui@...rosoft.com>
Cc:	"gregkh\@linuxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"driverdev-devel\@linuxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	"olaf\@aepfle.de" <olaf@...fle.de>,
	"apw\@canonical.com" <apw@...onical.com>,
	"jasowang\@redhat.com" <jasowang@...hat.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: Re: [PATCH] tools: hv: ignore ENOBUFS in the KVP daemon

Dexuan Cui <decui@...rosoft.com> writes:

>> -----Original Message-----
>> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
>> Sent: Wednesday, November 19, 2014 20:41 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 <decui@...rosoft.com> writes:
>> 
>> >> -----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().
>> 
>> 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)
>

Thanks!

> --- 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) {

Sorry for being pushy, but it seems ENOBUFS is also possible here (at
least man sendmsg mentions it).

> +                               syslog(LOG_ERR, "send error: ignored");
> +                               continue;
> +                       }
> +
>                         exit(EXIT_FAILURE);
>                 }
>         }
>
> Thanks,
> -- Dexuan

-- 
  Vitaly
--
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