Re: [PATCH v2] drm/gem: Fix GEM handle release errors

["Christian König" <christian.koenig@amd.com>]

Hi Jeffy,

Am 08.08.22 um 05:51 schrieb Chen Jeffy:
> Hi Christian,
>
> Thanks for your reply, and sorry i didn't make it clear.
>
> On 8/8 星期一 0:52, Christian König wrote:
>> Am 03.08.22 um 10:32 schrieb Jeffy Chen:
>>> Currently we are assuming a one to one mapping between dmabuf and 
>>> handle
>>> when releasing GEM handles.
>>>
>>> But that is not always true, since we would create extra handles for 
>>> the
>>> GEM obj in cases like gem_open() and getfb{,2}().
>>>
>>> A similar issue was reported at:
>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F20211105083308.392156-1-jay.xu%40rock-chips.com%2F&data=05%7C01%7Cchristian.koenig%40amd.com%7Cd7488e9f235041f7e84408da78f14882%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637955274964656400%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=9G2YbHcYUs1VQYyvjXwLzYawNw%2BP8i%2BjjPBSHx3r2yg%3D&reserved=0 
>>>
>>>
>>> Another problem is that the drm_gem_remove_prime_handles() now only
>>> remove handle to the exported dmabuf (gem_obj->dma_buf), so the 
>>> imported
>>> ones would leak:
>>> WARNING: CPU: 2 PID: 236 at drivers/gpu/drm/drm_prime.c:228 
>>> drm_prime_destroy_file_private+0x18/0x24
>>>
>>> Let's fix these by using handle to find the exact map to remove.
>>
>> Well we are clearly something missing here. As far as I can see the 
>> current code is correct.
>>
>> Creating multiple GEM handles for the same DMA-buf is possible, but 
>> illegal. >
>> In other words when a GEM handle is exported as DMA-buf and imported 
>> again you should intentionally always get the same handle.
>
> These issue are not about having handles for importing an exported 
> dma-buf case, but for having multiple handles to a GEM object(which 
> means having multiple handles to a dma-buf).
>
> I know the drm-prime is trying to make dma-buf and handle maps one to 
> one, but the drm-gem is allowing to create extra handles for a GEM 
> object, for example:
> drm_gem_open_ioctl -> drm_gem_handle_create_tail
> drm_mode_getfb2_ioctl -> drm_gem_handle_create
> drm_mode_getfb -> fb->funcs->create_handle

Yes, so far that's correct.

>
>
> So we are allowing GEM object to have multiple handles, and GEM object 
> could have at most one dma-buf, doesn't that means that dma-buf could 
> map to multiple handles?

No, at least not for the same GEM file private. That's the reason why 
the rb is indexed by the dma_buf object and not the handle.

In other words the rb is so that you have exactly one handle for each 
dma_buf in each file private.

>
> Or should we rewrite the GEM framework to limit GEM object with uniq 
> handle?

No, the extra handles are expected because when you call 
drm_mode_getfb*() and drm_gem_open_ioctl() the caller now owns the 
returned GEM handle.

>
> The other issue is that we are leaking dma-buf <-> handle map for the 
> imported dma-buf, since the drm_gem_remove_prime_handles doesn't take 
> care of obj->import_attach->dmabuf.

No, that's correct as well. obj->dma_buf is set even for imported 
DMA-buf objects. See drm_gem_prime_fd_to_handle().

Regards,
Christian.

>
> But of cause this can be fixed in other way:
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -180,6 +180,9 @@ drm_gem_remove_prime_handles(struct drm_gem_object 
> *obj, struct drm_file *filp)
> drm_prime_remove_buf_handle_locked(&filp->prime,
> obj->dma_buf);
>         }
> +       if (obj->import_attach)
> + drm_prime_remove_buf_handle_locked(&filp->prime,
> + obj->import_attach->dmabuf);
>         mutex_unlock(&filp->prime.lock);
>  }
>
>
>> So this is pretty much a clear NAK to this patch since it shouldn't 
>> be necessary or something is seriously broken somewhere else.
>>
>> Regards,
>> Christian.
>>
>>>
>>> Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
>>> ---
>>>
>>> Changes in v2:
>>> Fix a typo of rbtree.
>>>
>>>   drivers/gpu/drm/drm_gem.c      | 17 +----------------
>>>   drivers/gpu/drm/drm_internal.h |  4 ++--
>>>   drivers/gpu/drm/drm_prime.c    | 20 ++++++++++++--------
>>>   3 files changed, 15 insertions(+), 26 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>>> index eb0c2d041f13..ed39da383570 100644
>>> --- a/drivers/gpu/drm/drm_gem.c
>>> +++ b/drivers/gpu/drm/drm_gem.c
>>> @@ -168,21 +168,6 @@ void drm_gem_private_object_init(struct 
>>> drm_device *dev,
>>>   }
>>>   EXPORT_SYMBOL(drm_gem_private_object_init);
>>> -static void
>>> -drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct 
>>> drm_file *filp)
>>> -{
>>> -    /*
>>> -     * Note: obj->dma_buf can't disappear as long as we still hold a
>>> -     * handle reference in obj->handle_count.
>>> -     */
>>> -    mutex_lock(&filp->prime.lock);
>>> -    if (obj->dma_buf) {
>>> - drm_prime_remove_buf_handle_locked(&filp->prime,
>>> -                           obj->dma_buf);
>>> -    }
>>> -    mutex_unlock(&filp->prime.lock);
>>> -}
>>> -
>>>   /**
>>>    * drm_gem_object_handle_free - release resources bound to 
>>> userspace handles
>>>    * @obj: GEM object to clean up.
>>> @@ -253,7 +238,7 @@ drm_gem_object_release_handle(int id, void *ptr, 
>>> void *data)
>>>       if (obj->funcs->close)
>>>           obj->funcs->close(obj, file_priv);
>>> -    drm_gem_remove_prime_handles(obj, file_priv);
>>> +    drm_prime_remove_buf_handle(&file_priv->prime, id);
>>>       drm_vma_node_revoke(&obj->vma_node, file_priv);
>>>       drm_gem_object_handle_put_unlocked(obj);
>>> diff --git a/drivers/gpu/drm/drm_internal.h 
>>> b/drivers/gpu/drm/drm_internal.h
>>> index 1fbbc19f1ac0..7bb98e6a446d 100644
>>> --- a/drivers/gpu/drm/drm_internal.h
>>> +++ b/drivers/gpu/drm/drm_internal.h
>>> @@ -74,8 +74,8 @@ int drm_prime_fd_to_handle_ioctl(struct drm_device 
>>> *dev, void *data,
>>>   void drm_prime_init_file_private(struct drm_prime_file_private 
>>> *prime_fpriv);
>>>   void drm_prime_destroy_file_private(struct drm_prime_file_private 
>>> *prime_fpriv);
>>> -void drm_prime_remove_buf_handle_locked(struct 
>>> drm_prime_file_private *prime_fpriv,
>>> -                    struct dma_buf *dma_buf);
>>> +void drm_prime_remove_buf_handle(struct drm_prime_file_private 
>>> *prime_fpriv,
>>> +                 uint32_t handle);
>>>   /* drm_drv.c */
>>>   struct drm_minor *drm_minor_acquire(unsigned int minor_id);
>>> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
>>> index e3f09f18110c..bd5366b16381 100644
>>> --- a/drivers/gpu/drm/drm_prime.c
>>> +++ b/drivers/gpu/drm/drm_prime.c
>>> @@ -190,29 +190,33 @@ static int drm_prime_lookup_buf_handle(struct 
>>> drm_prime_file_private *prime_fpri
>>>       return -ENOENT;
>>>   }
>>> -void drm_prime_remove_buf_handle_locked(struct 
>>> drm_prime_file_private *prime_fpriv,
>>> -                    struct dma_buf *dma_buf)
>>> +void drm_prime_remove_buf_handle(struct drm_prime_file_private 
>>> *prime_fpriv,
>>> +                 uint32_t handle)
>>>   {
>>>       struct rb_node *rb;
>>> -    rb = prime_fpriv->dmabufs.rb_node;
>>> +    mutex_lock(&prime_fpriv->lock);
>>> +
>>> +    rb = prime_fpriv->handles.rb_node;
>>>       while (rb) {
>>>           struct drm_prime_member *member;
>>> -        member = rb_entry(rb, struct drm_prime_member, dmabuf_rb);
>>> -        if (member->dma_buf == dma_buf) {
>>> +        member = rb_entry(rb, struct drm_prime_member, handle_rb);
>>> +        if (member->handle == handle) {
>>>               rb_erase(&member->handle_rb, &prime_fpriv->handles);
>>>               rb_erase(&member->dmabuf_rb, &prime_fpriv->dmabufs);
>>> -            dma_buf_put(dma_buf);
>>> +            dma_buf_put(member->dma_buf);
>>>               kfree(member);
>>> -            return;
>>> -        } else if (member->dma_buf < dma_buf) {
>>> +            break;
>>> +        } else if (member->handle < handle) {
>>>               rb = rb->rb_right;
>>>           } else {
>>>               rb = rb->rb_left;
>>>           }
>>>       }
>>> +
>>> +    mutex_unlock(&prime_fpriv->lock);
>>>   }
>>>   void drm_prime_init_file_private(struct drm_prime_file_private 
>>> *prime_fpriv)
>>
>>
>