cvs commit: src/sys/kern kern_sig.c

[David Xu]

David Schultz wrote:

>You have to worry about that anyway, though.  A and B need to know
>that they're not allowed to hold locks across the calls if C calls
>msleep(), for instance.  Anyway, your proposal if having a flag
>for msleep() is basically the same as my proposal of having a
>separate function.  (The only difference is that adding a separate
>function doesn't break the ABI.)  So it sounds like we're more or
>less in agreement here.
>
>  
>
This is not a lock problem, this is the problem why a stack variable can not
be used when thread is going to sleep, this is a rather odd behavior to me.
For example,  thread A stack variable address p is put on a known place,
e.g, a queue,  thread A unlocks the lock of the queue and sleeps,
sometimes later, a producer thread B writes the data into memory pointed 
by p,
and wake up A, that's a very simple code, here malloc is not needed at all.
At the time, kernel shoudn't swap out the thread stack, any code trying 
to swap
it out is totally broken.

>>>The alternative, of course, is to just fix the code that assumes
>>>that swapping doesn't exist.
>>>
>>>      
>>>
>>First find all code written in such way, but it is not that easy.
>>    
>>
>
>True.  If we changed msleep() to disable swapping by default, then
>we wouldn't have to worry about correctness problems related to
>missing some.
>
>
>  
>