Re: [PATCHv2] kvm: fix race with level interrupts

From: Marcelo Tosatti
Date: Fri Jul 20 2012 - 15:23:12 EST

On Thu, Jul 19, 2012 at 01:45:20PM +0300, Michael S. Tsirkin wrote:
> When more than 1 source id is in use for the same GSI, we have the
> following race related to handling irq_states race:
> CPU 0 clears bit 0. CPU 0 read irq_state as 0. CPU 1 sets level to 1.
> CPU 1 calls kvm_ioapic_set_irq(1). CPU 0 calls kvm_ioapic_set_irq(0).
> Now ioapic thinks the level is 0 but irq_state is not 0.
> Fix by performing all irq_states bitmap handling under pic/ioapic lock.
> This also removes the need for atomics with irq_states handling.
> Reported-by: Gleb Natapov <gleb@xxxxxxxxxx>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---

Applied, thanks.

> Changes from v1:
> Address comments by Gleb and Alex:
> renamed some variables for clarify
> renamed kvm_irq_line_state -> __kvm_irq_line_state
> Any chance we can put this in 3.5? I know level IRQs are not widely
> used, which is likely why this went unnoticed for so long, but still ...

"From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

The thing is, I don't take bug fixes late in the -rc just because they
are bug fixes.

And I really shouldn't.

If it's an old bug, and doesn't cause an oops or a security issue, it
had damn well better wait for the next merge window. There is absolutely
_no_ reason to just blindly "fix bugs" at the end of the rc stage,
because quite frankly, the risks coming from fixing a bug is often
bigger than the advantage.

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