drm/nouveau/pm: fix a potential race condition when creating an engine context

There is always the possiblity that the ppm->context pointer would get
partially updated and accidentally would equal ctx. This would allow two
contexts to co-exist, which is not acceptable. Moving the test to the
critical section takes care of this problem.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Signed-off-by: Martin Peres <martin.peres@free.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/pm/base.c b/drivers/gpu/drm/nouveau/nvkm/engine/pm/base.c
index 274457ca3fef798d62b955d02a70cbd91e287cb0..4cf36a3aa81460c2c062b6cc41e70571530c1eb8 100644 (file)
--- a/drivers/gpu/drm/nouveau/nvkm/engine/pm/base.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/pm/base.c
@@ -358,12 +358,11 @@ nvkm_perfctx_ctor(struct nvkm_object *parent, struct nvkm_object *engine,
        mutex_lock(&nv_subdev(ppm)->mutex);
        if (ppm->context == NULL)
                ppm->context = ctx;
-       mutex_unlock(&nv_subdev(ppm)->mutex);
-
        if (ctx != ppm->context)
-               return -EBUSY;
+               ret = -EBUSY;
+       mutex_unlock(&nv_subdev(ppm)->mutex);
 
-       return 0;
+       return ret;
 }
 
 struct nvkm_oclass