Re: [PATCH 1/2] drm/i915: clear up wedged transitions

[Chris Wilson <chris@chris-wilson.co.uk>]

On Thu, Nov 15, 2012 at 05:17:22PM +0100, Daniel Vetter wrote:
> We have two important transitions of the wedged state in the current
> code:
> 
> - 0 -> 1: This means a hang has been detected, and signals to everyone
>   that they please get of any locks, so that the reset work item can
>   do its job.
> 
> - 1 -> 0: The reset handler has completed.
> 
> Now the last transition mixes up two states: "Reset completed and
> successful" and "Reset failed". To distinguish these two we do some
> tricks with the reset completion, but I simply could not convince
> myself that this doesn't race under odd circumstances.
> 
> Hence split this up, and add a new terminal state indicating that the
> hw is gone for good.
> 
> Also add explicit #defines for both states, update comments.
> 
> v2: Split out the reset handling bugfix for the throttle ioctl.
> 
> v3: s/tmp/wedged/ sugested by Chris Wilson. Also fixup up a rebase
> error which prevented this patch from actually compiling.
> 
> v4: To unify the wedged state with the reset counter, keep the
> reset-in-progress state just as a flag. The terminally-wedged state is
> now denoted with a big number.
> 
> v5: Add a comment to the reset_counter special values explaining that
> WEDGED & RESET_IN_PROGRESS needs to be true for the code to be
> correct.
> 
> v6: Fixup logic errors introduced with the wedged+reset_counter
> unification. Since WEDGED implies reset-in-progress (in a way we're
> terminally stuck in the dead-but-reset-not-completed state), we need
> ensure that we check for this everywhere. The specific bug was in
> wait_for_error, which would simply have timed out.
> 
> v7: Extract an inline i915_reset_in_progress helper to make the code
> more readable. Also annote the reset-in-progress case with an
> unlikely, to help the compiler optimize the fastpath. Do the same for
> the terminally wedged case with i915_terminally_wedged.
> 
> Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> @@ -1385,7 +1372,7 @@ out:
>  		/* If this -EIO is due to a gpu hang, give the reset code a
>  		 * chance to clean up the mess. Otherwise return the proper
>  		 * SIGBUS. */
> -		if (!atomic_read(&dev_priv->gpu_error.wedged))
> +		if (i915_terminally_wedged(&dev_priv->gpu_error))
>  			return VM_FAULT_SIGBUS;

(i915_gem_fault())

This if() is backwards.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre