[Intel-gfx] [PATCH] drm/i915: Fix an incorrect free rather than derefence issue.

[Daniel Vetter]

On Thu, Feb 12, 2015 at 12:29:21PM +0000, Nick Hoath wrote:
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88652
> 
> Signed-off-by: Nick Hoath <nicholas.hoath at intel.com>

Commit message is missing the absolutely crucial detail about which patch
introduced this regression:

commit 6d3d8274bc45de4babb62d64562d92af984dd238
Author:     Nick Hoath <nicholas.hoath at intel.com>
AuthorDate: Thu Jan 15 13:10:39 2015 +0000

    drm/i915: Subsume intel_ctx_submit_request in to drm_i915_gem_request

Another thing I've noticed is that we explicitly drop the context
reference for the request before dropping the request reference. Without
clearing the req->ctx pointer. That has a very high chance to leading to
tears, imo the context unreferenceing should be pushed into
i915_gem_request_free.

Except that it's there already, which means we have a double unref now?

Also this patch is for the legacy ringbuffer code, but the referenced bug
is for gen8+ execlists. We're definitely not running this code here I
think.

Imo step one is to drop all the explicit ctx refcounting for req->ctx and
always rely on the implicit reference. Then see what happens.

Cheers, Daniel


> ---
>  drivers/gpu/drm/i915/i915_drv.c | 2 +-
>  drivers/gpu/drm/i915/i915_gem.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 1765989..dc10d86 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2661,7 +2661,7 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv,
>  			intel_lr_context_unpin(ring, submit_req->ctx);
>  
>  		i915_gem_context_unreference(submit_req->ctx);
> -		kfree(submit_req);
> +		i915_gem_request_unreference(submit_req);
>  	}
>  
>  	/*
> -- 
> 2.1.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch