[Intel-gfx] [PATCH] drm/i915: irq handlers don't need interrupt-safe spinlocks

[Daniel Vetter]

On Thu, Jun 27, 2013 at 11:14 PM, Paulo Zanoni <przanoni at gmail.com> wrote:
> 2013/6/25 Daniel Vetter <daniel.vetter at ffwll.ch>:
>> Since we only have one interrupt handler and interrupt handlers are
>> non-reentrant.
>>
>> To drive the point really home give them all an _irq_handler suffix.
>
> Could we also add WARN(!in_irq()) or something equivalent for better
> protection? Big backtraces are a nice way to discover we did something
> wrong.

Lockdep checks hard/soft irq context constraints and will scream
horribly into dmesg if we get it wrong. So I don't think a in_irq
warning will add any value. Aside: hard/softirq isn't the only special
context lockdep checks for, it also checks for memory allocations,
e.g. if you hold a lock while calling kmalloc and your shrinker needs
the same locks it'll scream. That's why we have all the GFP_NORETRY
stuff when allocating memory and the trylock in the shrinker.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch