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

[Johannes Berg <johannes@xxxxxxxxxxxxxxxx>]

On Tue, 2012-05-29 at 16:29 -0700, Ben Greear wrote:
> On 05/29/2012 04:23 PM, Felix Fietkau wrote:
> > On 2012-05-30 1:02 AM, greearb@xxxxxxxxxxxxxxx wrote:
> >> From: Ben Greear<greearb@xxxxxxxxxxxxxxx>
> >>
> >> 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@xxxxxxxxxxxxxxx>
> > 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.

There used to be bugs in this area in mac80211 and/or pktgen, and I
remember crashing my machine very trivially. I don't think that this is
still a problem though, but I haven't tried in a long time. FWIW, the
time-frame of this must've been ~2-3 years ago.

johannes

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