Dexuan Cui <decui@xxxxxxxxxxxxx> writes:
>> -----Original Message-----
>> From: Vitaly Kuznetsov
>> Sent: Wednesday, November 19, 2014 18:50 PM
>> To: Dexuan Cui
>> Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; driverdev-
>> devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx;
>> jasowang@xxxxxxxxxx; 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
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