From: Danilo Krummrich <dakr@redhat.com>
To: Abhinav Singh <singhabhinav9051571833@gmail.com>
Cc: nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
daniel@ffwll.ch, linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Nouveau] [PATCH] driver: gpu: Fix warning directly dereferencing a rcu pointer
Date: Thu, 30 Nov 2023 00:52:42 +0100 [thread overview]
Message-ID: <f5a69710-f1a6-444d-9d2a-7c07589a2bdc@redhat.com> (raw)
In-Reply-To: <20231126145723.388162-1-singhabhinav9051571833@gmail.com>
Hi Abhinav,
Thanks for sending this follow-up patch.
On 11/26/23 15:57, Abhinav Singh wrote:
> Fix a sparse warning with this message
> "warning:dereference of noderef expression". In this context it means we
> are dereferencing a __rcu tagged pointer directly.
>
> We should not be directly dereferencing a rcu pointer. To get a normal
> (non __rcu tagged pointer) from a __rcu tagged pointer we are using the
> function unrcu_pointer(...). The non __rcu tagged pointer then can be
> dereferenced just like a normal pointer.
Can you please add a brief explanation why unrcu_pointer() is fine here?
>
> 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.
How is that relevant for this patch?
- Danilo
>
> Signed-off-by: Abhinav Singh <singhabhinav9051571833@gmail.com>
> ---
> drivers/gpu/drm/nouveau/nv10_fence.c | 2 +-
> drivers/gpu/drm/nouveau/nv84_fence.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nv10_fence.c b/drivers/gpu/drm/nouveau/nv10_fence.c
> index c6a0db5b9e21..845b64c079ed 100644
> --- a/drivers/gpu/drm/nouveau/nv10_fence.c
> +++ b/drivers/gpu/drm/nouveau/nv10_fence.c
> @@ -32,7 +32,7 @@
> int
> nv10_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_MTHD(push, NV06E, SET_REFERENCE, fence->base.seqno);
> diff --git a/drivers/gpu/drm/nouveau/nv84_fence.c b/drivers/gpu/drm/nouveau/nv84_fence.c
> index 812b8c62eeba..d42e72e23dec 100644
> --- a/drivers/gpu/drm/nouveau/nv84_fence.c
> +++ b/drivers/gpu/drm/nouveau/nv84_fence.c
> @@ -85,7 +85,7 @@ nv84_fence_chid(struct nouveau_channel *chan)
> static int
> nv84_fence_emit(struct nouveau_fence *fence)
> {
> - struct nouveau_channel *chan = fence->channel;
> + struct nouveau_channel *chan = unrcu_pointer(fence->channel);
> struct nv84_fence_chan *fctx = chan->fence;
> u64 addr = fctx->vma->addr + nv84_fence_chid(chan) * 16;
>
next prev parent reply other threads:[~2023-11-29 23:52 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-26 14:57 [PATCH] driver: gpu: Fix warning directly dereferencing a rcu pointer Abhinav Singh
2023-11-29 23:52 ` Danilo Krummrich [this message]
2023-12-03 8:11 ` Abhinav Singh
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