From: Abhinav Singh <singhabhinav9051571833@gmail.com>
To: Danilo Krummrich <dakr@redhat.com>,
kherbst@redhat.com, lyude@redhat.com, airlied@gmail.com,
daniel@ffwll.ch
Cc: nouveau@lists.freedesktop.org,
linux-kernel-mentees@lists.linuxfoundation.org,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v3] driver: gpu: Fixing warning directly dereferencing a rcu pointer
Date: Tue, 21 Nov 2023 14:29:58 +0530 [thread overview]
Message-ID: <38a45214-7cd0-482a-a330-65c5be488fba@gmail.com> (raw)
In-Reply-To: <0754e669-8b00-461c-b6fe-79c659bf59a3@redhat.com>
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@gmail.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
prev parent reply other threads:[~2024-01-16 11:47 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-13 8:10 [PATCH] driver: gpu: Fixing warning directly dereferencing a rcu pointer Abhinav Singh
2023-11-13 8:24 ` [Nouveau] " Maarten Lankhorst
2023-11-13 17:10 ` Danilo Krummrich
2023-11-13 18:37 ` [PATCH v2] drivers: gpu: Fixing warning directly dereferencing a rcu pointer v2 Abhinav Singh
2023-11-13 18:42 ` [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer Abhinav Singh
2023-11-13 18:49 ` [Nouveau] " Danilo Krummrich
2023-11-13 18:55 ` Abhinav Singh
2023-11-13 19:00 ` [Nouveau] " Danilo Krummrich
2023-11-13 19:13 ` [PATCH v3] " Abhinav Singh
2023-11-13 19:31 ` Abhinav Singh
2023-11-21 1:20 ` [Nouveau] " Danilo Krummrich
2023-11-21 8:59 ` Abhinav Singh [this message]
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