cvs commit: src/sys/sys mutex.h

[John Baldwin]

On 14-Oct-2003 Jeff Roberson wrote:
> On Tue, 14 Oct 2003, John Baldwin wrote:
> 
>>
>> On 12-Oct-2003 Jeff Roberson wrote:
>> > jeff        2003/10/12 14:02:55 PDT
>> >
>> >   FreeBSD src repository
>> >
>> >   Modified files:
>> >     sys/sys              mutex.h
>> >   Log:
>> >    - Implement a mtx_ownedby() macro which can be used to determine if a
>> >      particular thread owns a mutex.  This cannot be done without races
>> >      unless the thread is curthread.
>>
>> This is a very bad idea.  What use do you have for this that is not
>> already handled by mtx_owned() or a mutex assertion?
> 
> I know it is racy in most contexts.  I use it to check to see if a thread
> on the runq owns giant.  Since I have the sched lock it isn't racy but
> even if it was it wouldn't matter in this case.

sched lock doesn't keep it from being racy.  Uncontested acquire and
releases don't go anywhere near sched lock.  Are you checking a
non-curthread thread pointer?  Maybe you could just do it for curthread
and that would be enough for your heuristic, i.e.

        if (thread == curthread && mtx_owned(&Giant)) {
                ...
        }

I'm just worried that if this is there someone is going to use it. :(

-- 

John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/