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    SubjectRe: [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer
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    Hi,

    thanks for sending a v2.

    On 11/13/23 19:42, Abhinav Singh wrote:
    > This patch fixes a sparse warning with this message
    > "warning:dereference of noderef expression". In this context it means we
    > are dereferencing a __rcu tagged pointer directly.

    Better use imperative here, e.g. "Fix a sparse warning ...".

    Wouldn't ask you to send a v3 for that alone...

    >
    > We should not be directly dereferencing a rcu pointer, rather we should
    > be using rcu helper function rcu_dereferece() inside rcu read critical
    > section to get a normal pointer which can be dereferenced.

    ...but this doesn't seem accurate anymore as well.

    - Danilo

    >
    > I tested with qemu with this command
    > qemu-system-x86_64 \
    > -m 2G \
    > -smp 2 \
    > -kernel bzImage \
    > -append "console=ttyS0 root=/dev/sda earlyprintk=serial net.ifnames=0" \
    > -drive file=bullseye.img,format=raw \
    > -net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \
    > -net nic,model=e1000 \
    > -enable-kvm \
    > -nographic \
    > -pidfile vm.pid \
    > 2>&1 | tee vm.log
    > with lockdep enabled.
    >
    > Signed-off-by: Abhinav Singh <singhabhinav9051571833@gmail.com>
    > ---
    > v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and
    > also removed the rcu locking and unlocking function call.
    >
    > drivers/gpu/drm/nouveau/nv04_fence.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/drivers/gpu/drm/nouveau/nv04_fence.c b/drivers/gpu/drm/nouveau/nv04_fence.c
    > index 5b71a5a5cd85..cdbc75e3d1f6 100644
    > --- a/drivers/gpu/drm/nouveau/nv04_fence.c
    > +++ b/drivers/gpu/drm/nouveau/nv04_fence.c
    > @@ -39,7 +39,7 @@ struct nv04_fence_priv {
    > static int
    > nv04_fence_emit(struct nouveau_fence *fence)
    > {
    > - struct nvif_push *push = fence->channel->chan.push;
    > + struct nvif_push *push = unrcu_pointer(fence->channel)->chan.push;
    > int ret = PUSH_WAIT(push, 2);
    > if (ret == 0) {
    > PUSH_NVSQ(push, NV_SW, 0x0150, fence->base.seqno);

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