Hey,
Den 2023-11-13 kl. 09:10, skrev Abhinav Singh:
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, rather we should
be using rcu helper function rcu_dereferece() inside rcu read critical
section to get a normal pointer which can be dereferenced.
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>
---
drivers/gpu/drm/nouveau/nv04_fence.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/nouveau/nv04_fence.c b/drivers/gpu/drm/nouveau/nv04_fence.c
index 5b71a5a5cd85..e62bad1ac720 100644
--- a/drivers/gpu/drm/nouveau/nv04_fence.c
+++ b/drivers/gpu/drm/nouveau/nv04_fence.c
@@ -39,7 +39,9 @@ struct nv04_fence_priv {
static int
nv04_fence_emit(struct nouveau_fence *fence)
{
- struct nvif_push *push = fence->channel->chan.push;
+ rcu_read_lock();
+ struct nvif_push *push = rcu_dereference(fence->channel)->chan.push;
+ rcu_read_unlock();
int ret = PUSH_WAIT(push, 2);
if (ret == 0) {
PUSH_NVSQ(push, NV_SW, 0x0150, fence->base.seqno);
I'm not an expert in nouveau fence channel lifetime, but I'm pretty sure
this should probably be a rcu_dereference_protected, since a fence
likely can't lose its channel before its command to signal is submitted.
But in case it's not, I would at least advise to check for
fence->channel lifetime before submitting a patch like this. At least
the original code warned about it not being 100% correct.
Cheers,
~Maarten
