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Re: PATCH: Always use ll/sc for mips
On Mon, Jul 08, 2002 at 10:21:56AM -0700, Jun Sun wrote:
> > No, Sony's ABI isn't MP proof and will break silently on MP systems. As
> > such I can't consider it anything else but a hack. sysmips(MIPS_ATOMIC_SET,
> > ...) and ll/sc however are MP proof.
> >
>
>
> sysmips(MIPS_ATOMIC_SET, ...) as it is is not MP-safe. Two processors can
> set the variable at the same time since no spinlock is used to protect the
> access.
Note there are two cases in the code, one using ll/sc which is MP proof
and a second implementation for machines that don't have these instructions.
At least for now Linux/MIPS SMP systems by definition have ll/sc, so I
don't see any problem.
> This is also a problem when I was writing preemptiable kernel patch.
Thanks for the reminder. I'm just working on the merge with 2.5.4 which
has all the preemption stuff. Another one for the to-do list ...
Ralf