[Intel-gfx] [PATCH] drm/i915: Convert breadcrumbs spinlock to be irqsafe

[Tvrtko Ursulin]

On 28/10/16 11:42, Chris Wilson wrote:
> On Fri, Oct 28, 2016 at 11:27:43AM +0100, Tvrtko Ursulin wrote:
>>
>>
>> On 28/10/16 11:10, Chris Wilson wrote:
>>> On Fri, Oct 28, 2016 at 10:42:22AM +0100, Tvrtko Ursulin wrote:
>>>>
>>>>
>>>> On 27/10/16 17:10, Chris Wilson wrote:
>>>>> The breadcrumbs are about to be used from within IRQ context sections,
>>>>> therefore we need to employ the irqsafe spinlock variants.
>>>>>
>>>>> (This is split out of the defer global seqno allocation patch due to
>>>>> realisation that we need a more complete conversion if we want to defer
>>>>> request submission even further.)
>>>
>>> [snip]
>>>
>>>> Assuming I got the above right and you agree to change it:
>>>
>>> You made me go and reduce them to _bh as appropriate anyway!!!
>>
>> Hm, but can't enable signalling be called with irqs disabled when
>> fences are exported?
>
> Yes, but that supercedes the spin_lock_bh, so we can just call
> spin_lock() in enabling_signaling as we can assert that we will always
> be called with irqs disabled here (due to spin_lock_irqsafe(fence->lock)
> in the callpath).

But as long as the b->lock is taken in the irqs disabled section 
somewhere, other callers like signaller thread, debugfs, etc, cannot 
just take it with _bh.

Regards,

Tvrtko