PERFORCE change 103633 for review
Robert Watson
rwatson at FreeBSD.org
Fri Aug 11 17:20:47 UTC 2006
On Fri, 11 Aug 2006, John Baldwin wrote:
>> I think the main problem (which is now fixed) was with this:
>>
>> copyin(addr, val1);
>> if (val1 == val2)
>> ....
>>
>> being non-atomic. On the other hand I tried to use other locks other then
>> Giant and it didnt work. I hope to investigate that later. Now I have this
>> working and my focus is elsewhere.
>
> No, what you have done is wrong. The idea of doing copyin() and then
> compare is just plain not going to work. :) You will need to use casuptr()
> or the like similar to the umtx code. This is assuming that a futex can be
> manipulated from userland w/o entering the kernel.
I assume that we can basically just do whatever Linux does here for
synchronization...
Robert N M Watson
Computer Laboratory
University of Cambridge
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