[PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage

[PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage

[Jesse.Zhang]

Add a NULL pointer check in ttm_resource_manager_usage() to prevent
kernel NULL pointer dereferences when the function is called with
an uninitialized resource manager.

This fixes a kernel OOPS observed on APU devices where the VRAM
resource manager is not fully initialized, but various sysfs and
debug interfaces still attempt to query VRAM usage statistics.

The crash backtrace showed:
    BUG: kernel NULL pointer dereference, address: 00000000000008f8
    Call Trace:
     amdttm_resource_manager_usage+0x1f/0x40 [amdttm]
     amdgpu_mem_info_vram_used_show+0x1e/0x40 [amdgpu]
     dev_attr_show+0x1d/0x40
     kernfs_seq_show+0x27/0x30

By returning 0 for NULL managers, we allow callers to safely query
usage information even when the underlying resource manager is not
available, which is the expected behavior for devices without
dedicated VRAM like APUs.

Suggested-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
---
 drivers/gpu/drm/ttm/ttm_resource.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
index e2c82ad07eb4..e4d45f75e40a 100644
--- a/drivers/gpu/drm/ttm/ttm_resource.c
+++ b/drivers/gpu/drm/ttm/ttm_resource.c
@@ -587,6 +587,9 @@ uint64_t ttm_resource_manager_usage(struct ttm_resource_manager *man)
 {
 	uint64_t usage;
 
+	if (!man)
+		return 0;
+
 	spin_lock(&man->bdev->lru_lock);
 	usage = man->usage;
 	spin_unlock(&man->bdev->lru_lock);
-- 
2.49.0

RE: [PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage

[Lazar, Lijo]

[AMD Official Use Only - AMD Internal Distribution Only]

The specific issue of trace with amdgpu_mem_info_vram_used_show should be fixed with this one - "drm/amdgpu: hide VRAM sysfs attributes on GPUs without VRAM"

Thanks,
Lijo
>-----Original Message-----
>From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of
>Jesse.Zhang
>Sent: Monday, October 13, 2025 7:25 AM
>To: amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
><Christian.Koenig@amd.com>; Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>Yang, Philip <Philip.Yang@amd.com>; Zhang, Jesse(Jie)
><Jesse.Zhang@amd.com>
>Subject: [PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage
>
>Add a NULL pointer check in ttm_resource_manager_usage() to prevent kernel
>NULL pointer dereferences when the function is called with an uninitialized
>resource manager.
>
>This fixes a kernel OOPS observed on APU devices where the VRAM resource
>manager is not fully initialized, but various sysfs and debug interfaces still
>attempt to query VRAM usage statistics.
>
>The crash backtrace showed:
>    BUG: kernel NULL pointer dereference, address: 00000000000008f8
>    Call Trace:
>     amdttm_resource_manager_usage+0x1f/0x40 [amdttm]
>     amdgpu_mem_info_vram_used_show+0x1e/0x40 [amdgpu]
>     dev_attr_show+0x1d/0x40
>     kernfs_seq_show+0x27/0x30
>
>By returning 0 for NULL managers, we allow callers to safely query usage
>information even when the underlying resource manager is not available, which
>is the expected behavior for devices without dedicated VRAM like APUs.
>
>Suggested-by: Philip Yang <Philip.Yang@amd.com>
>Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
>---
> drivers/gpu/drm/ttm/ttm_resource.c | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/drivers/gpu/drm/ttm/ttm_resource.c
>b/drivers/gpu/drm/ttm/ttm_resource.c
>index e2c82ad07eb4..e4d45f75e40a 100644
>--- a/drivers/gpu/drm/ttm/ttm_resource.c
>+++ b/drivers/gpu/drm/ttm/ttm_resource.c
>@@ -587,6 +587,9 @@ uint64_t ttm_resource_manager_usage(struct
>ttm_resource_manager *man)  {
>       uint64_t usage;
>
>+      if (!man)
>+              return 0;
>+
>       spin_lock(&man->bdev->lru_lock);
>       usage = man->usage;
>       spin_unlock(&man->bdev->lru_lock);
>--
>2.49.0

RE: [PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage

[Zhang, Jesse(Jie)]

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Lazar, Lijo <Lijo.Lazar@amd.com>
> Sent: Monday, October 13, 2025 12:37 PM
> To: Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>; amd-gfx@lists.freedesktop.org;
> dri-devel@lists.freedesktop.org
> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
> <Christian.Koenig@amd.com>; Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
> Yang, Philip <Philip.Yang@amd.com>; Zhang, Jesse(Jie)
> <Jesse.Zhang@amd.com>
> Subject: RE: [PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage
>
> [AMD Official Use Only - AMD Internal Distribution Only]
>
> The specific issue of trace with amdgpu_mem_info_vram_used_show should be
> fixed with this one - "drm/amdgpu: hide VRAM sysfs attributes on GPUs without
> VRAM"
Thanks @Lazar, Lijo,  maybe we still can use this patch to fix  this crash when calling  AMDGPU_CS and  query AMDGPU_INFO_VRAM_USAGE.
or add check like the previous patch.

Regards
Jesse

[  911.954646] BUG: kernel NULL pointer dereference, address: 00000000000008f8 [  911.962437]
#PF: supervisor write access in kernel mode [  912.007045] RIP: 0010:_raw_spin_lock+0x1e/0x40
 [  912.105151]  amdttm_resource_manager_usage+0x1f/0x40
 [amdttm] [  912.111579]  amdgpu_cs_parser_bos.isra.0+0x543/0x800 [amdgpu]

>
> Thanks,
> Lijo
> >-----Original Message-----
> >From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of
> >Jesse.Zhang
> >Sent: Monday, October 13, 2025 7:25 AM
> >To: amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
> >Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
> ><Christian.Koenig@amd.com>; Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
> >Yang, Philip <Philip.Yang@amd.com>; Zhang, Jesse(Jie)
> ><Jesse.Zhang@amd.com>
> >Subject: [PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage
> >
> >Add a NULL pointer check in ttm_resource_manager_usage() to prevent
> >kernel NULL pointer dereferences when the function is called with an
> >uninitialized resource manager.
> >
> >This fixes a kernel OOPS observed on APU devices where the VRAM
> >resource manager is not fully initialized, but various sysfs and debug
> >interfaces still attempt to query VRAM usage statistics.
> >
> >The crash backtrace showed:
> >    BUG: kernel NULL pointer dereference, address: 00000000000008f8
> >    Call Trace:
> >     amdttm_resource_manager_usage+0x1f/0x40 [amdttm]
> >     amdgpu_mem_info_vram_used_show+0x1e/0x40 [amdgpu]
> >     dev_attr_show+0x1d/0x40
> >     kernfs_seq_show+0x27/0x30
> >
> >By returning 0 for NULL managers, we allow callers to safely query
> >usage information even when the underlying resource manager is not
> >available, which is the expected behavior for devices without dedicated VRAM like
> APUs.
> >
> >Suggested-by: Philip Yang <Philip.Yang@amd.com>
> >Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
> >---
> > drivers/gpu/drm/ttm/ttm_resource.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> >diff --git a/drivers/gpu/drm/ttm/ttm_resource.c
> >b/drivers/gpu/drm/ttm/ttm_resource.c
> >index e2c82ad07eb4..e4d45f75e40a 100644
> >--- a/drivers/gpu/drm/ttm/ttm_resource.c
> >+++ b/drivers/gpu/drm/ttm/ttm_resource.c
> >@@ -587,6 +587,9 @@ uint64_t ttm_resource_manager_usage(struct
> >ttm_resource_manager *man)  {
> >       uint64_t usage;
> >
> >+      if (!man)
> >+              return 0;
> >+
> >       spin_lock(&man->bdev->lru_lock);
> >       usage = man->usage;
> >       spin_unlock(&man->bdev->lru_lock);
> >--
> >2.49.0
>

RE: [PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage

[Lazar, Lijo]

[AMD Official Use Only - AMD Internal Distribution Only]

>-----Original Message-----
>From: Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>
>Sent: Monday, October 13, 2025 11:25 AM
>To: Lazar, Lijo <Lijo.Lazar@amd.com>; amd-gfx@lists.freedesktop.org; dri-
>devel@lists.freedesktop.org
>Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
><Christian.Koenig@amd.com>; Yang, Philip <Philip.Yang@amd.com>
>Subject: RE: [PATCH] drm/ttm: Add NULL check in
>ttm_resource_manager_usage
>
>[AMD Official Use Only - AMD Internal Distribution Only]
>
>> -----Original Message-----
>> From: Lazar, Lijo <Lijo.Lazar@amd.com>
>> Sent: Monday, October 13, 2025 12:37 PM
>> To: Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>> amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
>> <Christian.Koenig@amd.com>; Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>> Yang, Philip <Philip.Yang@amd.com>; Zhang, Jesse(Jie)
>> <Jesse.Zhang@amd.com>
>> Subject: RE: [PATCH] drm/ttm: Add NULL check in
>> ttm_resource_manager_usage
>>
>> [AMD Official Use Only - AMD Internal Distribution Only]
>>
>> The specific issue of trace with amdgpu_mem_info_vram_used_show should
>> be fixed with this one - "drm/amdgpu: hide VRAM sysfs attributes on
>> GPUs without VRAM"
>Thanks @Lazar, Lijo,  maybe we still can use this patch to fix  this crash when
>calling  AMDGPU_CS and  query AMDGPU_INFO_VRAM_USAGE.
>or add check like the previous patch.
>
[lijo]

Agree, there are indeed multiple places of ttm_resource_manager_usage call. You may follow the same check as in the hide VRAM patch - ttm_resource_manager_used - in case ttm doesn't take this change.

Thanks,
Lijo

>Regards
>Jesse
>
>[  911.954646] BUG: kernel NULL pointer dereference, address:
>00000000000008f8 [  911.962437]
>#PF: supervisor write access in kernel mode [  912.007045] RIP:
>0010:_raw_spin_lock+0x1e/0x40  [  912.105151]
>amdttm_resource_manager_usage+0x1f/0x40
> [amdttm] [  912.111579]  amdgpu_cs_parser_bos.isra.0+0x543/0x800
>[amdgpu]
>
>>
>> Thanks,
>> Lijo
>> >-----Original Message-----
>> >From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of
>> >Jesse.Zhang
>> >Sent: Monday, October 13, 2025 7:25 AM
>> >To: amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>> >Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
>> ><Christian.Koenig@amd.com>; Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>> >Yang, Philip <Philip.Yang@amd.com>; Zhang, Jesse(Jie)
>> ><Jesse.Zhang@amd.com>
>> >Subject: [PATCH] drm/ttm: Add NULL check in
>> >ttm_resource_manager_usage
>> >
>> >Add a NULL pointer check in ttm_resource_manager_usage() to prevent
>> >kernel NULL pointer dereferences when the function is called with an
>> >uninitialized resource manager.
>> >
>> >This fixes a kernel OOPS observed on APU devices where the VRAM
>> >resource manager is not fully initialized, but various sysfs and
>> >debug interfaces still attempt to query VRAM usage statistics.
>> >
>> >The crash backtrace showed:
>> >    BUG: kernel NULL pointer dereference, address: 00000000000008f8
>> >    Call Trace:
>> >     amdttm_resource_manager_usage+0x1f/0x40 [amdttm]
>> >     amdgpu_mem_info_vram_used_show+0x1e/0x40 [amdgpu]
>> >     dev_attr_show+0x1d/0x40
>> >     kernfs_seq_show+0x27/0x30
>> >
>> >By returning 0 for NULL managers, we allow callers to safely query
>> >usage information even when the underlying resource manager is not
>> >available, which is the expected behavior for devices without
>> >dedicated VRAM like
>> APUs.
>> >
>> >Suggested-by: Philip Yang <Philip.Yang@amd.com>
>> >Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
>> >---
>> > drivers/gpu/drm/ttm/ttm_resource.c | 3 +++
>> > 1 file changed, 3 insertions(+)
>> >
>> >diff --git a/drivers/gpu/drm/ttm/ttm_resource.c
>> >b/drivers/gpu/drm/ttm/ttm_resource.c
>> >index e2c82ad07eb4..e4d45f75e40a 100644
>> >--- a/drivers/gpu/drm/ttm/ttm_resource.c
>> >+++ b/drivers/gpu/drm/ttm/ttm_resource.c
>> >@@ -587,6 +587,9 @@ uint64_t ttm_resource_manager_usage(struct
>> >ttm_resource_manager *man)  {
>> >       uint64_t usage;
>> >
>> >+      if (!man)
>> >+              return 0;
>> >+
>> >       spin_lock(&man->bdev->lru_lock);
>> >       usage = man->usage;
>> >       spin_unlock(&man->bdev->lru_lock);
>> >--
>> >2.49.0
>>
>

RE: [PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage

[Lazar, Lijo]

[Public]

>-----Original Message-----
>From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of Lazar,
>Lijo
>Sent: Monday, October 13, 2025 12:39 PM
>To: Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>; amd-
>gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
><Christian.Koenig@amd.com>; Yang, Philip <Philip.Yang@amd.com>
>Subject: RE: [PATCH] drm/ttm: Add NULL check in
>ttm_resource_manager_usage
>
>[AMD Official Use Only - AMD Internal Distribution Only]
>
>>-----Original Message-----
>>From: Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>
>>Sent: Monday, October 13, 2025 11:25 AM
>>To: Lazar, Lijo <Lijo.Lazar@amd.com>; amd-gfx@lists.freedesktop.org;
>>dri- devel@lists.freedesktop.org
>>Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
>><Christian.Koenig@amd.com>; Yang, Philip <Philip.Yang@amd.com>
>>Subject: RE: [PATCH] drm/ttm: Add NULL check in
>>ttm_resource_manager_usage
>>
>>[AMD Official Use Only - AMD Internal Distribution Only]
>>
>>> -----Original Message-----
>>> From: Lazar, Lijo <Lijo.Lazar@amd.com>
>>> Sent: Monday, October 13, 2025 12:37 PM
>>> To: Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>>> amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>>> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
>>> <Christian.Koenig@amd.com>; Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>>> Yang, Philip <Philip.Yang@amd.com>; Zhang, Jesse(Jie)
>>> <Jesse.Zhang@amd.com>
>>> Subject: RE: [PATCH] drm/ttm: Add NULL check in
>>> ttm_resource_manager_usage
>>>
>>> [AMD Official Use Only - AMD Internal Distribution Only]
>>>
>>> The specific issue of trace with amdgpu_mem_info_vram_used_show
>>> should be fixed with this one - "drm/amdgpu: hide VRAM sysfs
>>> attributes on GPUs without VRAM"
>>Thanks @Lazar, Lijo,  maybe we still can use this patch to fix  this
>>crash when calling  AMDGPU_CS and  query AMDGPU_INFO_VRAM_USAGE.
>>or add check like the previous patch.
>>
>[lijo]
>
>Agree, there are indeed multiple places of ttm_resource_manager_usage call.
>You may follow the same check as in the hide VRAM patch -
>ttm_resource_manager_used - in case ttm doesn't take this change.
>

On a second look,

struct amdgpu_vram_mgr {
        struct ttm_resource_manager manager;

Hence this won't work for something like this -

        case AMDGPU_INFO_VRAM_USAGE:
                ui64 = ttm_resource_manager_usage(&adev->mman.vram_mgr.manager);

Thanks,
Lijo

>Thanks,
>Lijo
>
>>Regards
>>Jesse
>>
>>[  911.954646] BUG: kernel NULL pointer dereference, address:
>>00000000000008f8 [  911.962437]
>>#PF: supervisor write access in kernel mode [  912.007045] RIP:
>>0010:_raw_spin_lock+0x1e/0x40  [  912.105151]
>>amdttm_resource_manager_usage+0x1f/0x40
>> [amdttm] [  912.111579]  amdgpu_cs_parser_bos.isra.0+0x543/0x800
>>[amdgpu]
>>
>>>
>>> Thanks,
>>> Lijo
>>> >-----Original Message-----
>>> >From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of
>>> >Jesse.Zhang
>>> >Sent: Monday, October 13, 2025 7:25 AM
>>> >To: amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>>> >Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig,
>>> >Christian <Christian.Koenig@amd.com>; Zhang, Jesse(Jie)
>>> ><Jesse.Zhang@amd.com>; Yang, Philip <Philip.Yang@amd.com>; Zhang,
>>> >Jesse(Jie) <Jesse.Zhang@amd.com>
>>> >Subject: [PATCH] drm/ttm: Add NULL check in
>>> >ttm_resource_manager_usage
>>> >
>>> >Add a NULL pointer check in ttm_resource_manager_usage() to prevent
>>> >kernel NULL pointer dereferences when the function is called with an
>>> >uninitialized resource manager.
>>> >
>>> >This fixes a kernel OOPS observed on APU devices where the VRAM
>>> >resource manager is not fully initialized, but various sysfs and
>>> >debug interfaces still attempt to query VRAM usage statistics.
>>> >
>>> >The crash backtrace showed:
>>> >    BUG: kernel NULL pointer dereference, address: 00000000000008f8
>>> >    Call Trace:
>>> >     amdttm_resource_manager_usage+0x1f/0x40 [amdttm]
>>> >     amdgpu_mem_info_vram_used_show+0x1e/0x40 [amdgpu]
>>> >     dev_attr_show+0x1d/0x40
>>> >     kernfs_seq_show+0x27/0x30
>>> >
>>> >By returning 0 for NULL managers, we allow callers to safely query
>>> >usage information even when the underlying resource manager is not
>>> >available, which is the expected behavior for devices without
>>> >dedicated VRAM like
>>> APUs.
>>> >
>>> >Suggested-by: Philip Yang <Philip.Yang@amd.com>
>>> >Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
>>> >---
>>> > drivers/gpu/drm/ttm/ttm_resource.c | 3 +++
>>> > 1 file changed, 3 insertions(+)
>>> >
>>> >diff --git a/drivers/gpu/drm/ttm/ttm_resource.c
>>> >b/drivers/gpu/drm/ttm/ttm_resource.c
>>> >index e2c82ad07eb4..e4d45f75e40a 100644
>>> >--- a/drivers/gpu/drm/ttm/ttm_resource.c
>>> >+++ b/drivers/gpu/drm/ttm/ttm_resource.c
>>> >@@ -587,6 +587,9 @@ uint64_t ttm_resource_manager_usage(struct
>>> >ttm_resource_manager *man)  {
>>> >       uint64_t usage;
>>> >
>>> >+      if (!man)
>>> >+              return 0;
>>> >+
>>> >       spin_lock(&man->bdev->lru_lock);
>>> >       usage = man->usage;
>>> >       spin_unlock(&man->bdev->lru_lock);
>>> >--
>>> >2.49.0
>>>
>>

Re: [PATCH] drm/ttm: Add NULL check in ttm_resource_manager_usage

[Christian König]

On 13.10.25 09:09, Lazar, Lijo wrote:
> [AMD Official Use Only - AMD Internal Distribution Only]
> 
>> -----Original Message-----
>> From: Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>
>> Sent: Monday, October 13, 2025 11:25 AM
>> To: Lazar, Lijo <Lijo.Lazar@amd.com>; amd-gfx@lists.freedesktop.org; dri-
>> devel@lists.freedesktop.org
>> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
>> <Christian.Koenig@amd.com>; Yang, Philip <Philip.Yang@amd.com>
>> Subject: RE: [PATCH] drm/ttm: Add NULL check in
>> ttm_resource_manager_usage
>>
>> [AMD Official Use Only - AMD Internal Distribution Only]
>>
>>> -----Original Message-----
>>> From: Lazar, Lijo <Lijo.Lazar@amd.com>
>>> Sent: Monday, October 13, 2025 12:37 PM
>>> To: Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>>> amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>>> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
>>> <Christian.Koenig@amd.com>; Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>>> Yang, Philip <Philip.Yang@amd.com>; Zhang, Jesse(Jie)
>>> <Jesse.Zhang@amd.com>
>>> Subject: RE: [PATCH] drm/ttm: Add NULL check in
>>> ttm_resource_manager_usage
>>>
>>> [AMD Official Use Only - AMD Internal Distribution Only]
>>>
>>> The specific issue of trace with amdgpu_mem_info_vram_used_show should
>>> be fixed with this one - "drm/amdgpu: hide VRAM sysfs attributes on
>>> GPUs without VRAM"
>> Thanks @Lazar, Lijo,  maybe we still can use this patch to fix  this crash when
>> calling  AMDGPU_CS and  query AMDGPU_INFO_VRAM_USAGE.
>> or add check like the previous patch.
>>
> [lijo]
> 
> Agree, there are indeed multiple places of ttm_resource_manager_usage call. You may follow the same check as in the hide VRAM patch - ttm_resource_manager_used - in case ttm doesn't take this change.

Yeah, agree.

When the VRAM manager isn't initialized we shouldn't be calling any of its functions in the first place.

Maybe it is a good idea to add something like "if (WARN_ON_ONCE(!man)) return 0;" to prevent the crashes and only get a nice warning into the system log.

Regards,
Christian.

> 
> Thanks,
> Lijo
> 
>> Regards
>> Jesse
>>
>> [  911.954646] BUG: kernel NULL pointer dereference, address:
>> 00000000000008f8 [  911.962437]
>> #PF: supervisor write access in kernel mode [  912.007045] RIP:
>> 0010:_raw_spin_lock+0x1e/0x40  [  912.105151]
>> amdttm_resource_manager_usage+0x1f/0x40
>> [amdttm] [  912.111579]  amdgpu_cs_parser_bos.isra.0+0x543/0x800
>> [amdgpu]
>>
>>>
>>> Thanks,
>>> Lijo
>>>> -----Original Message-----
>>>> From: amd-gfx <amd-gfx-bounces@lists.freedesktop.org> On Behalf Of
>>>> Jesse.Zhang
>>>> Sent: Monday, October 13, 2025 7:25 AM
>>>> To: amd-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org
>>>> Cc: Deucher, Alexander <Alexander.Deucher@amd.com>; Koenig, Christian
>>>> <Christian.Koenig@amd.com>; Zhang, Jesse(Jie) <Jesse.Zhang@amd.com>;
>>>> Yang, Philip <Philip.Yang@amd.com>; Zhang, Jesse(Jie)
>>>> <Jesse.Zhang@amd.com>
>>>> Subject: [PATCH] drm/ttm: Add NULL check in
>>>> ttm_resource_manager_usage
>>>>
>>>> Add a NULL pointer check in ttm_resource_manager_usage() to prevent
>>>> kernel NULL pointer dereferences when the function is called with an
>>>> uninitialized resource manager.
>>>>
>>>> This fixes a kernel OOPS observed on APU devices where the VRAM
>>>> resource manager is not fully initialized, but various sysfs and
>>>> debug interfaces still attempt to query VRAM usage statistics.
>>>>
>>>> The crash backtrace showed:
>>>>    BUG: kernel NULL pointer dereference, address: 00000000000008f8
>>>>    Call Trace:
>>>>     amdttm_resource_manager_usage+0x1f/0x40 [amdttm]
>>>>     amdgpu_mem_info_vram_used_show+0x1e/0x40 [amdgpu]
>>>>     dev_attr_show+0x1d/0x40
>>>>     kernfs_seq_show+0x27/0x30
>>>>
>>>> By returning 0 for NULL managers, we allow callers to safely query
>>>> usage information even when the underlying resource manager is not
>>>> available, which is the expected behavior for devices without
>>>> dedicated VRAM like
>>> APUs.
>>>>
>>>> Suggested-by: Philip Yang <Philip.Yang@amd.com>
>>>> Signed-off-by: Jesse Zhang <jesse.zhang@amd.com>
>>>> ---
>>>> drivers/gpu/drm/ttm/ttm_resource.c | 3 +++
>>>> 1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/ttm/ttm_resource.c
>>>> b/drivers/gpu/drm/ttm/ttm_resource.c
>>>> index e2c82ad07eb4..e4d45f75e40a 100644
>>>> --- a/drivers/gpu/drm/ttm/ttm_resource.c
>>>> +++ b/drivers/gpu/drm/ttm/ttm_resource.c
>>>> @@ -587,6 +587,9 @@ uint64_t ttm_resource_manager_usage(struct
>>>> ttm_resource_manager *man)  {
>>>>       uint64_t usage;
>>>>
>>>> +      if (!man)
>>>> +              return 0;
>>>> +
>>>>       spin_lock(&man->bdev->lru_lock);
>>>>       usage = man->usage;
>>>>       spin_unlock(&man->bdev->lru_lock);
>>>> --
>>>> 2.49.0
>>>
>>
>