Re: [linuxsh-dev] [PATCH] Preemptible kernel for SH

[Robert Love <rml@tech9.net>]

On Mon, 2001-12-03 at 16:16, Jeremy Siegel wrote:
> Just FYI... the preemptible kernel depends on non-preemptible critical regions
> denoted by spinlock calls (see Robert Love's excellent summary in
> Documentation/preempt-locking.txt).  Many common drivers are assumed to have
> correct locking for SMP operation, but non-SMP drivers may not. I've only run
> the PreK SH kernel on the Solution Engine w/Ethernet and serial, but I did not
> yet check to see if additional locks might be required in drivers/char/sh-sci.c
> or drivers/net/stnic.c, which are specific to SH platforms and thus not SMP-safe
> otherwise.

Ahh, good point.  Similar situation occured on ARM when it went
preemptive.  Thankfully, Russel King and company try to properly lock
things even if they are no ops.

Coding under a preemptive kernel means more than what
Documentation/preempt-locking.txt implies ... you have to protect data
regions as if you are operating under SMP.

It is good practice, anyhow.

This means you can include linux/spinlock.h and use the locking
constructs as needed.  Under a normal UP kernel, they will compile
away.  Under a preemptive kernel, they will provide the needed
reentrancy protection.  If there ever is a an SMP SH kernel (or
something like it) the kernel will be ready for the future.

	Robert Love