Recurring traffic/authentication freeze - detailed information (pt1)

Bryan Phillippe Bryan.Phillippe at
Thu Feb 16 15:34:07 EST 2012

On Feb 11, 2012, at 1:04 AM, Jouni Malinen wrote:

> 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.


I think you are right.  After updating my compat-wireless package to "the
latest" (as of a few days ago), this monitor-blocking problem can no
longer be reproduced.  So hostapd appears to be off the hook. :)

Unfortunately, compat-wireless updates are usually a two steps forward and
one step backward ordeal; although this problem is gone, I'm seeing other
problems now that I wasn't previously.  But those will be directed to a
different mailing list. ;)

Kind regards,

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