Messages in this thread | | | Date | Mon, 12 Mar 2001 19:37:54 +0000 | From | Adrian Cox <> | Subject | Re: static scheduling - SCHED_IDLE? |
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Jamie Lokier wrote:
> Adrian Cox wrote:
>> Jamie Lokier's suggestion of raising priority when in the kernel doesn't >> help. You need to raise the priority of the task which is currently in >> userspace and will call up() next time it enters the kernel. You don't >> know which task that is.
> Dear oh dear. I was under the impression that kernel semaphores are > supposed to be used as mutexes only -- there are other mechanisms for > signalling between processes.
I think most of the kernel semaphores are used as mutexes, with occasional producer/consumer semaphores. I think the core kernel code is fine, the risk mostly comes from miscellaneous character devices. I've written code that does this for a specialised device driver. I wanted only one process to have the device open at once, and for others to block on open. Using semaphores meant that multiple shells could do "cat > /dev/mywidget" and be serialised.
Locking up users of this strange piece of hardware doesn't bring down the system, so your suggestion could work. We need a big fat warning in semaphore.h, and a careful examination of the current code.
- Adrian
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