Re: [PATCH] mac80211: Limit number of pending skbs.

[Ben Greear <greearb@candelatech.com>]

On 05/29/2012 04:23 PM, Felix Fietkau wrote:
> On 2012-05-30 1:02 AM, greearb@candelatech.com wrote:
>> From: Ben Greear<greearb@candelatech.com>
>>
>> Current code will allow any number of pending skbs, and
>> this can OOM the system when used with something like
>> the pktgen tool (which may not back off properly if
>> queue is stopped).
>>
>> Possibly this is just a bug in our version of pktgen,
>> but either way, it seems reasonable to add a limit
>> so that it is not possible to go OOM in this manner.
>>
>> Signed-off-by: Ben Greear<greearb@candelatech.com>
> Adding a module parameter in a workaround for a possibly broken module
> seems a bit excessive to me.
>
> Also, I'm not sure adding such a silent packet drop is a good idea. At
> the very least, it should complain loudly to encourage people to fix the
> actual bug instead of just papering over it.
>
> When the driver cannot accept more packets, the queue stop should
> prevent the network stack from spamming mac80211 with more packets. Your
> pktgen seems to be ignoring this, so please fix it instead of adding
> workarounds to mac80211.

Ok, I'll work on pktgen next time I get a chance.

I recall I had to add a hack (that was not wanted upstream)
to get pktgen to even work with mac80211 interfaces w/out crashing
the kernel, so probably no one else is using it anyway.

I did verify that with user-space UDP sockets running at similar
speed the pending buffers did not fill up at all.

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com