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

["Xu, Quan" <quan.xu@xxxxxxxxx>]

On March 09, 2016 9:56pm, <JBeulich@xxxxxxxx> wrote:
> >>> 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, thanks.
Now I got it. btw, I also find a good explanation from the comment, inside 
check_lock(), in xen/common/spinlock.c.
Quan


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