Recurring traffic/authentication freeze - detailed information (pt1)

Jouni Malinen j at
Sat Feb 11 04:04:49 EST 2012

On Tue, Feb 07, 2012 at 01:17:01AM +0000, Bryan Phillippe wrote:
> However, I have noticed something else worth reporting... when running
> hostapd-0.7.3, I found that occasionally the sendmsg() in driver_nl80211.c
> wpa_driver_nl80211_send_frame() would block *forever*, resulting in dead
> wireless.  I posted about this but nobody had any idea, so I just changed
> the code to make the socket non-blocking and then exit(1) if the
> sendmsg() failed with EAGAIN.  After upgrading to the new hostapd-2.0-devel,
> this same problem bit me again - stalling in sendmsg() forever, analogous
> location (wpa_driver_nl80211_send_mntr()).  So I suspect this is probably
> NOT hostapd's fault, or I'd guess that many other people would have seen
> it?  So do you or anyone else have advice on how I can debug this problem?
> I have already added some code to my kernel socket implementation to log a
> message when the write is blocked on a blocking socket, and I can see it's
> because the write queue is full.  I'd like to figure out who the likely
> owner of this bug is so I can work with them to resolve it.

I would not expect the monitor interface to behave this way and as such,
this sounds like a kernel issue to me.. Though, you may have some
problems getting people interested to look at this since the use of
monitor interfaces with hostapd is going away. In other words, if you
were to update your kernel to the latest snapshot, you would not even
hit this function in hostapd anymore.
Jouni Malinen                                            PGP id EFC895FA

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