Re: [Xen-devel] [PATCH v2 1/2] IOMMU/spinlock: Fix a bug found in AMD IOMMU initialization.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.03.16 at 14:46, <quan.xu@xxxxxxxxx> wrote:
> Now I am still not clear for this point- "this inconsistency might lead to 
> deadlock".
> I think it is similar to 'mixing interrupt disabled and enabled spinlocks is 
> something we disallow'.
> I hope you can give me an example about how to lead to deadlock. 

The implication from disabling interrupts while acquiring a lock
is that the lock is also being acquired by some interrupt
handler. If you mix acquire types, the one not disabling
interrupts is prone to be interrupted, and the interrupt trying
to get hold of the lock the same CPU already owns.

Jan


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