On 24 Feb 2006, Andi Kleen wrote:
> Alan Stern <[email protected]> writes:
>
> > This patch (as658) makes the idle_notifier in x86_64 and idle_chain in
> > s390 into atomic notifier chains rather than blocking chains. This is
> > necessary because they are called during IRQ handling as CPUs leave and
> > enter the idle state.
>
> Actually they aren't. While the code is called from the interrupt
> handler logically it belong to the idle thread, not the interrupt handler.
> They are only called when the interrupt directly interrupts the idle
> thread, so no atomicity needed.
In do_IRQ() there's a call to exit_idle(), which calls __exit_idle(),
which runs the idle_notifier call chain. Surely you're not saying that we
can do a down_read() in this pathway?
And actually the chain's type doesn't seem to make much difference, since
at the moment there's nothing in the vanilla kernel that registers for the
idle_notifier chain.
> -Andi
>
> P.S.: Please cc maintainers in the future.
Yes, I should have sent the patch to you too. I apologize.
Alan Stern
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