Re: [Xen-devel] [PATCH] VMX: avoid taking locks with irqs disabled

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

Oh yes. That's a class of race that I hadn't realised would be introduced by
the new rendezvous code. Spinlocks which are ever taken with IRQs disabled
must *always* be taken with IRQs disabled. Spinlocks which are ever taken
with IRQs enabled must *always* be taken with IRQs enabled.

It's quite an extra constraint on spinlock usage actually. :-(

Actually this new partitioning of locks into two equivalence classes is
begging for some run-time checking in debug builds. I'll sort out a patch
for that.

 -- Keir

On 20/10/08 10:30, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx> wrote:

> Shuffle the bits of the vmexit handler that run with EFLAGS.IF == 0 up
> to the top.  Otherwise we end up calling spin_lock() with interrupts
> disabled, which can deadlock against the time-synchronization rendezvous
> code.
> 
> Signed-off-by: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
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