Re: [mac80211] BUG_ON with current -git (4.8.0-11417-g24532f7)
From: Ard Biesheuvel
Date: Fri Oct 14 2016 - 05:36:07 EST
On 14 October 2016 at 10:25, Johannes Berg <johannes@xxxxxxxxxxxxxxxx> wrote:
> On Fri, 2016-10-14 at 10:21 +0100, Ard Biesheuvel wrote:
>> It is annotated with a TODO, though :-)
>> 38320c70d282b (Herbert Xu 2008-01-28 19:35:05
>> -0800 41)
>> * TODO: Use spare space in skb for this where possible.
> I saw that, but I don't think generally there will be spare space for
> it - the stuff there is likely far too big. Anyway ... same problem
> that we have.
> I'm not inclined to allocate ~500 bytes temporarily for every frame
> either though.
> Maybe we could try to manage it in mac80211, we'd "only" need 5 AEAD
> structs (which are today on the stack) in parallel for each key (4 TX,
> 1 RX), but in a typical case of having 3 keys that's already 7.5K worth
> of memory that we almost never use. Again, with more complexity, we
> could know that the TX will not be used if the driver does the TX, but
> the single RX one we'd need unconditionally... decisions decisions...
So why is the performance hit acceptable for ESP but not for WPA? We
could easily implement the same thing, i.e., kmalloc(GFP_ATOMIC)/kfree
the aead_req struct rather than allocate it on the stack