Re: 'ip' blocking for long time trying to down station

[Johannes Berg <johannes@sipsolutions.net>]

Hi Ben,

Sorry for the late reply.

> This is on the 400 station test machine.  No more crashes, but I'm seeing long
> pauses (10+ seconds) when trying to down station interfaces (and sometimes other
> commands as well).  The system cannot stabilize (my user-space app times out
> after a while due to blocking on system() calls such as the one below,
> and gives up, causing endless loops of up/down, associate, dhcp, etc)
> I'm going to tweak the user-space code more to try to bring up stations
> in smaller batches, but it still seems like there is room for improvement
> in the OS.
> 
> Using sysrq, I got this trace of the command.  I'm not sure it was blocked
> in the same place the whole time, but it seems likely.  Any ideas for how
> to speed this sort of thing up?
> 
> ./local/sbin/ip link set sta140 down
> 

>   [<ffffffff81070e2e>] flush_work+0x2b/0x34
>   [<ffffffff8106f857>] ? cwq_dec_nr_in_flight+0x76/0x76
>   [<ffffffffa026a673>] ieee80211_do_stop+0x379/0x544 [mac80211]

I'm guessing that the other interfaces are actually re-scheduling work
items while this is trying to flush ... I'm not really sure how to
improve this behaviour though.

johannes