Re: linuxthreads/spinlock.c bug

[Wolfram Gloger <wmglo at dent dot med dot uni-muenchen dot de>]

>E.g. suppose
>you evaluate the head pointer while the list looks like this:
>
>    X -> Y -> Z -> 0
>
>Meanwhile some other threads comes along and do:
>
>(pop X)
>
>    Y -> Z -> 0
>
>(pop Y)
>
>    Z -> 0

>(push X)
>
>    X -> Z -> 0
>
> So now the original thread's compare_and_swap can still succeed, due
> to the match on the X, even though the list is different now.

Hmm, to me it looks like you are right.  You mean that wait_node_alloc
could erroneously put Y 'back' on the free list, even though it has
been removed/used by another thread.  Bad.

> I propose to scrap the ``optimization'' in wait_node_alloc/free and just
> use malloc/free directly.

Couldn't we just use the code conditional on !HAS_COMPARE_AND_SWAP
with the spinlock?  Isn't there the assumption elsewhere that
wait_node's are never actually free()d?

Regards,
Wolfram.