* [PATCH] driver: gpu: Fixing warning directly dereferencing a rcu pointer
@ 2023-11-13 8:10 Abhinav Singh
2023-11-13 8:24 ` Maarten Lankhorst
0 siblings, 1 reply; 12+ messages in thread
From: Abhinav Singh @ 2023-11-13 8:10 UTC (permalink / raw)
To: kherbst, lyude, dakr, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees, 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@gmail.com>
---
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);
--
2.39.2
^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-13 8:10 [PATCH] driver: gpu: Fixing warning directly dereferencing a rcu pointer Abhinav Singh
@ 2023-11-13 8:24 ` Maarten Lankhorst
2023-11-13 17:10 ` Danilo Krummrich
0 siblings, 1 reply; 12+ messages in thread
From: Maarten Lankhorst @ 2023-11-13 8:24 UTC (permalink / raw)
To: Abhinav Singh, kherbst, lyude, dakr, airlied, daniel
Cc: nouveau, linux-kernel-mentees, linux-kernel, dri-devel
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@gmail.com>
> ---
> 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
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-13 8:24 ` 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
0 siblings, 2 replies; 12+ messages in thread
From: Danilo Krummrich @ 2023-11-13 17:10 UTC (permalink / raw)
To: Maarten Lankhorst, Abhinav Singh, kherbst, lyude, airlied, daniel
Cc: nouveau, linux-kernel-mentees, linux-kernel, dri-devel
On 11/13/23 09:24, Maarten Lankhorst wrote:
> 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@gmail.com>
>> ---
>> 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.
Yes, before nouveau_fence_emit() did not add this fence to the fence context's
pending list ->channel doesn't need any protection. We can probably just use
unrcu_pointer(), as in [1].
[1] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/nouveau/nouveau_fence.c#L210
>
> 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
>
^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH v2] drivers: gpu: Fixing warning directly dereferencing a rcu pointer v2
2023-11-13 17:10 ` Danilo Krummrich
@ 2023-11-13 18:37 ` Abhinav Singh
2023-11-13 18:42 ` [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer Abhinav Singh
1 sibling, 0 replies; 12+ messages in thread
From: Abhinav Singh @ 2023-11-13 18:37 UTC (permalink / raw)
To: kherbst, lyude, dakr, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees, 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@gmail.com>
---
v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and
also removed the rcu locking and unlocking function call.
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);
--
2.39.2
^ permalink raw reply related [flat|nested] 12+ messages in thread
* [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer
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 ` Abhinav Singh
2023-11-13 18:49 ` Danilo Krummrich
1 sibling, 1 reply; 12+ messages in thread
From: Abhinav Singh @ 2023-11-13 18:42 UTC (permalink / raw)
To: kherbst, lyude, dakr, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees, 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@gmail.com>
---
v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and
also removed the rcu locking and unlocking function call.
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);
--
2.39.2
^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-13 18:42 ` [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer Abhinav Singh
@ 2023-11-13 18:49 ` Danilo Krummrich
2023-11-13 18:55 ` Abhinav Singh
0 siblings, 1 reply; 12+ messages in thread
From: Danilo Krummrich @ 2023-11-13 18:49 UTC (permalink / raw)
To: Abhinav Singh, kherbst, lyude, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees
Hi,
thanks for sending a v2.
On 11/13/23 19:42, 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.
Better use imperative here, e.g. "Fix a sparse warning ...".
Wouldn't ask you to send a v3 for that alone...
>
> 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.
...but this doesn't seem accurate anymore as well.
- Danilo
>
> 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>
> ---
> v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and
> also removed the rcu locking and unlocking function call.
>
> 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);
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-13 18:49 ` Danilo Krummrich
@ 2023-11-13 18:55 ` Abhinav Singh
2023-11-13 19:00 ` Danilo Krummrich
0 siblings, 1 reply; 12+ messages in thread
From: Abhinav Singh @ 2023-11-13 18:55 UTC (permalink / raw)
To: Danilo Krummrich, kherbst, lyude, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees
On 11/14/23 00:19, Danilo Krummrich wrote:
> Hi,
>
> thanks for sending a v2.
>
> On 11/13/23 19:42, 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.
>
> Better use imperative here, e.g. "Fix a sparse warning ...".
>
> Wouldn't ask you to send a v3 for that alone...
>
>>
>> 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.
>
> ...but this doesn't seem accurate anymore as well.
>
> - Danilo
>
>>
>> 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>
>> ---
>> v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and
>> also removed the rcu locking and unlocking function call.
>>
>> 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);
>
Hi maintainers thanks a lot for reviewing this patch.
I think I should fix my mistake by sending in another patch so that the
code changes and description matches. So should I send another patch ?
Thank You,
Abhinav Singh
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH v2] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-13 18:55 ` Abhinav Singh
@ 2023-11-13 19:00 ` Danilo Krummrich
2023-11-13 19:13 ` [PATCH v3] " Abhinav Singh
0 siblings, 1 reply; 12+ messages in thread
From: Danilo Krummrich @ 2023-11-13 19:00 UTC (permalink / raw)
To: Abhinav Singh, kherbst, lyude, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees
On 11/13/23 19:55, Abhinav Singh wrote:
> On 11/14/23 00:19, Danilo Krummrich wrote:
>> Hi,
>>
>> thanks for sending a v2.
>>
>> On 11/13/23 19:42, 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.
>>
>> Better use imperative here, e.g. "Fix a sparse warning ...".
>>
>> Wouldn't ask you to send a v3 for that alone...
>>
>>>
>>> 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.
>>
>> ...but this doesn't seem accurate anymore as well.
>>
>> - Danilo
>>
>>>
>>> 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>
>>> ---
>>> v1 -> v2 : Replaced the rcu_dereference(...) with unrcu_pointer(...) and
>>> also removed the rcu locking and unlocking function call.
>>>
>>> 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);
>>
> Hi maintainers thanks a lot for reviewing this patch.
> I think I should fix my mistake by sending in another patch so that the code changes and description matches. So should I send another patch ?
Yes, please send a v3.
>
> Thank You,
> Abhinav Singh
>
^ permalink raw reply [flat|nested] 12+ messages in thread
* [PATCH v3] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-13 19:00 ` Danilo Krummrich
@ 2023-11-13 19:13 ` Abhinav Singh
2023-11-13 19:31 ` Abhinav Singh
2023-11-21 1:20 ` Danilo Krummrich
0 siblings, 2 replies; 12+ messages in thread
From: Abhinav Singh @ 2023-11-13 19:13 UTC (permalink / raw)
To: kherbst, lyude, dakr, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees, 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. 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>
---
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);
--
2.39.2
^ permalink raw reply related [flat|nested] 12+ messages in thread
* Re: [PATCH v3] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-13 19:13 ` [PATCH v3] " Abhinav Singh
@ 2023-11-13 19:31 ` Abhinav Singh
2023-11-21 1:20 ` Danilo Krummrich
1 sibling, 0 replies; 12+ messages in thread
From: Abhinav Singh @ 2023-11-13 19:31 UTC (permalink / raw)
To: kherbst, lyude, dakr, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees
On 11/14/23 00:43, 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>
> ---
> 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);
Hi, just for the sake of my own confirmation, the patch is merge ready
right? once the CI runs successfully it will be merged right?
Thank You,
Abhinav Singh
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH v3] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-13 19:13 ` [PATCH v3] " Abhinav Singh
2023-11-13 19:31 ` Abhinav Singh
@ 2023-11-21 1:20 ` Danilo Krummrich
2023-11-21 8:59 ` Abhinav Singh
1 sibling, 1 reply; 12+ messages in thread
From: Danilo Krummrich @ 2023-11-21 1:20 UTC (permalink / raw)
To: Abhinav Singh, kherbst, lyude, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees
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);
^ permalink raw reply [flat|nested] 12+ messages in thread
* Re: [PATCH v3] driver: gpu: Fixing warning directly dereferencing a rcu pointer
2023-11-21 1:20 ` Danilo Krummrich
@ 2023-11-21 8:59 ` Abhinav Singh
0 siblings, 0 replies; 12+ messages in thread
From: Abhinav Singh @ 2023-11-21 8:59 UTC (permalink / raw)
To: Danilo Krummrich, kherbst, lyude, airlied, daniel
Cc: dri-devel, nouveau, linux-kernel, linux-kernel-mentees
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
^ permalink raw reply [flat|nested] 12+ messages in thread
end of thread, other threads:[~2023-11-21 9:00 UTC | newest]
Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-11-13 8:10 [PATCH] driver: gpu: Fixing warning directly dereferencing a rcu pointer Abhinav Singh
2023-11-13 8:24 ` 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 ` Danilo Krummrich
2023-11-13 18:55 ` Abhinav Singh
2023-11-13 19:00 ` Danilo Krummrich
2023-11-13 19:13 ` [PATCH v3] " Abhinav Singh
2023-11-13 19:31 ` Abhinav Singh
2023-11-21 1:20 ` Danilo Krummrich
2023-11-21 8:59 ` Abhinav Singh
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