Re: [lwip-users] Bug in pbuf.c regarding PBUF_POOL

[Jonathan Larmour]

Leon Woestenberg wrote:
> Hello all,
>
> this is very late reply.
>
> On Sun, 2006-10-22 at 07:44 +0100, Kieran Mansley wrote:
>
> > On Fri, Oct 20, 2006 at 11:37:23PM +0100, Jonathan Larmour wrote:
> >
> > > With the current code, I think the only solution is SYS_LIGHTWEIGHT_PROT. 
> > > My opinion is that the !SYS_LIGHTWEIGHT_PROT stuff should probably just be 
> > > removed.
> >
> > Thanks for the detailed post - good to see folks getting to grips with
> > the stack.  The above seemed to summarise quite nicely and I agree
> > completely with that.
>
> I completely agree with you; It's good to see there is interest in the
> lwIP stack from developers that are concerned abouts its correctness.
>
> The SYS_LIGHTWEIGHT_PROT protection was introduced by one of the
> developers using the stack to protect *ONLY* between interrupt context
> and single-thread user-space context if I am not mistaken.
>
> I am all for removing it, because the locking solution does not scale
> across different platforms.

I was actually arguing the other way round I'm afraid :-). I was arguing 
that it looks to me that SYS_LIGHTWEIGHT_PROT is essentially mandatory 
because packets arrive asynchronously and so pbuf allocation needs to have 
some protection no matter what since the allocation will take place from a 
device driver. That would be true whatever the context, or whether single 
or multi-threaded.

The !SYS_LIGHTWEIGHT_PROT code simply doesn't give any thread or interrupt 
safety at all. So in fact the !SYS_LIGHTWEIGHT_PROT code does not appear 
to solve the problem it seems intended to solve. Hence me saying that that 
code should be removed entirely since as far as I can tell it doesn't 
achieve anything. If protection is needed, something using 
SYS_LIGHTWEIGHT_PROT is the solution.

Jifl
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