Re: start_kernel(): bug: interrupts were enabled early

Matthew Wilcox
2010-03-31T21:17:59Z

On Wed, Mar 31, 2010 at 02:05:00PM -0700, H. Peter Anvin wrote:
> What I note is that lib/rwsem-spinlock.c seems to be rather inconsistent
> in its use of spin_lock_irqsave/spin_lock_irqrestore versus
> spin_lock_irq/spin_unlock_irq... in fact, __down_read is the *only*
> place where we use the latter as opposed to the former.
>
> Is that a bug? If so, it would certainly explain this behavior.

It's based on down_read() and down_write() not being callable from
interrupt context, or with interrupts disabled (since they can sleep).
up_read(), up_write(), down_read_trylock(), down_write_trylock(),
downgrade_write() can all be called from interrupt context since they
cannot sleep.

--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."