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Date:   Sat, 9 Dec 2017 01:01:57 +0100
From:   Adam Borowski <kilobyte@...band.pl>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     bskeggs@...hat.com, airlied@...ux.ie,
        dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, daniel.thompson@...aro.org,
        masami.hiramatsu@...aro.org
Subject: Re: [PATCH] drm/nouveau/imem/nv50: fix incorrect use of refcount API

On Fri, Dec 08, 2017 at 06:30:34PM +0000, Ard Biesheuvel wrote:
> Commit be55287aa5b ("drm/nouveau/imem/nv50: embed nvkm_instobj directly
> into nv04_instobj") introduced some new calls to the refcount api to
> the nv50 mapping code. In one particular instance, it does the
> following:
> 
>     if (!refcount_inc_not_zero(&iobj->maps)) {
>             ...
>             refcount_inc(&iobj->maps);
>     }
> 
> i.e., it calls refcount_inc() to increment the refcount when it is known
> to be zero, which is explicitly forbidden by the API. Instead, use
> refcount_set() to set it to 1.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---

Awesome!  Works for me.

> Apologies if this was already found and fixed. I don't usually follow
> the DRM or nouveau mailing lists.

I see nothing relevant in dri-devel and nouveau archives, except my
complaint (GTX 560 Ti (GF114)):
https://lists.freedesktop.org/archives/nouveau/2017-December/029264.html
and Richard Narron seconding it (MSI GeForce 210):
https://lists.freedesktop.org/archives/nouveau/2017-December/029276.html

>  drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c b/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c
> index 1ba7289684aa..db48a1daca0c 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/instmem/nv50.c
> @@ -249,7 +249,7 @@ nv50_instobj_acquire(struct nvkm_memory *memory)
>  			iobj->base.memory.ptrs = &nv50_instobj_fast;
>  		else
>  			iobj->base.memory.ptrs = &nv50_instobj_slow;
> -		refcount_inc(&iobj->maps);
> +		refcount_set(&iobj->maps, 1);
>  	}
>  
>  	mutex_unlock(&imem->subdev.mutex);
> -- 

I'm just a dumb user here, my tags don't carry a weight, but Tested-by:.


Meow!
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