Re: [2.4.17/18pre] VM and swap - it's really unusable

Oliver Neukum
2002-01-15T09:21:33Z

On Tuesday 15 January 2002 08:10, george anzinger wrote:

> Yes, this is classic priority inversion. It is here now, today with
> semaphors which are held by code that blocks. If the code doesn't
> block, why not use a spin lock? If it does, well the problem is here

Because eg. other code that holds the semaphore needs to sleep

> now. I suppose we could set a preempt disable around a semaphore if it
> makes you feel better. It doesn't fix the problem if the task blocks

It would make me feel better, but it would defeat the purpose.
There's a lot of code holding semaphores.

> AND it is legal to block while holding a preemption lock.

But it's easier to fix. If you can preempt only by explicitely
sleeping, you can beat priority invasion by changing basically
only wake_up. If you can be preempted at random, you need to know
who holds a semaphore.

Regards
Oliver