[Intel-gfx] [PATCH 4/7] drm/i915: no hangcheck when reset is in progress

[Daniel Vetter]

On Wed, Jul 03, 2013 at 05:22:09PM +0300, Mika Kuoppala wrote:
> From: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> 
> The timer for hangchecking can run again before the previous
> reset it has triggered has been handled. This can corrupt
> the hangcheck state as reset handling will access and write to
> the hangcheck data. To prevent this, avoid running the hangcheck
> logic while reset is in progress.
> 
> Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> Reviewed-by: Ben Widawsky <ben at bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_irq.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index dc1b878..b0fec7f 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2447,6 +2447,9 @@ void i915_hangcheck_elapsed(unsigned long data)
>  	if (!i915_enable_hangcheck)
>  		return;
>  
> +	if (i915_reset_in_progress(&dev_priv->gpu_error))
> +		return;

atomic_t are weakly-ordered (I know, we're on x86 here ...) and I think
we're missing the requisite amount of barriers to keep races at bay.

I think wrapping up all access to the hangcheck stats (both from the
hangcheck timer and in the reset code and eventually in the readout code)
with an irq-save spinlock is the simpler and much more obviously correct
(and hence safer) option. Note that you can't optimize away the irq
save/restore stuff in the timer since we call the hangcheck stuff also
from hardirq context.

So I'll punt on this patch here for now, merged all the others leading up
to this one here.

Thanks, Daniel

> +
>  	for_each_ring(ring, dev_priv, i) {
>  		u32 seqno, acthd;
>  		bool busy = true;
> -- 
> 1.7.9.5
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch