linux-kernel - [PATCH] drm/nouveau/imem/nv50: fix incorrect use of refcount API

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Date:   Fri,  8 Dec 2017 18:30:34 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     bskeggs@...hat.com, airlied@...ux.ie,
        dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     daniel.thompson@...aro.org, masami.hiramatsu@...aro.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: [PATCH] drm/nouveau/imem/nv50: fix incorrect use of refcount API

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>
---

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

 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);
-- 
2.11.0