Re: [PATCH v3] driver: gpu: Fixing warning directly dereferencing a rcu pointer

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 11/21/23 06:50, Danilo Krummrich wrote:
On 11/13/23 20:13, 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.

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.

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@xxxxxxxxx>

Applied, thanks!

There are a few more such occurrences. [1][2] Plan to fix them as well?

[1] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nv10_fence.c#L35 [2] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nv84_fence.c#L88

---
v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and
            also removed the rcu locking and unlocking function call.
v2 -> v3 : Changed the description of the patch to match it with the actual
       implementation.

  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);

Thanks a lot for merging this.
Yeah sure I will submit the patch for the issues soon.

Regards,
Abhinav Singh



[Index of Archives]     [Linux DRI Users]     [Linux Intel Graphics]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [XFree86]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux