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Date: Tue, 21 Nov 2023 14:29:58 +0530 From: Abhinav Singh <singhabhinav9051571833@...il.com> To: Danilo Krummrich <dakr@...hat.com>, kherbst@...hat.com, lyude@...hat.com, airlied@...il.com, daniel@...ll.ch Cc: dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org, linux-kernel-mentees@...ts.linuxfoundation.org Subject: Re: [PATCH v3] driver: gpu: Fixing warning directly dereferencing a rcu pointer 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@...il.com> > > 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
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