Dexuan Cui <de...@microsoft.com> writes:
>> -----Original Message-----
>> From: Vitaly Kuznetsov [mailto:vkuzn...@redhat.com]
>> Sent: Wednesday, November 19, 2014 20:41 PM
>> To: Dexuan Cui
>> Cc: gre...@linuxfoundation.org; linux-kernel@vger.kernel.org; driverdev-
>> de...@linuxdriverproject.org; o...@aepfle.de; a...@canonical.com;
>> jasow...@redhat.com; Haiyang Zhang
>> Subject: Re: [PATCH] tools: hv: ignore ENOBUFS in the KVP daemon
>>
>> Dexuan Cui <de...@microsoft.com> writes:
>>
>> >> -----Original Message-----
>> >> From: Vitaly Kuznetsov
>> >> Sent: Wednesday, November 19, 2014 18:50 PM
>> >> To: Dexuan Cui
>> >> Cc: gre...@linuxfoundation.org; linux-kernel@vger.kernel.org;
>> driverdev-
>> >> de...@linuxdriverproject.org; o...@aepfle.de; a...@canonical.com;
>> >> jasow...@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)
>
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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