Date:   Tue, 9 Aug 2022 16:54:24 +0800
From:   Chen Jeffy <jeffy.chen@...k-chips.com>
To:     Christian König <christian.koenig@....com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Andy Yan <andy.yan@...k-chips.com>,
        Jianqun Xu <jay.xu@...k-chips.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        linux-media@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v2] drm/gem: Fix GEM handle release errors

Hi Christian,

On 8/9 星期二 15:55, Christian König wrote:
> Am 09.08.22 um 03:28 schrieb Chen Jeffy:
>> Hi Christian,
>>
>> On 8/9 星期二 2:03, Christian König wrote:
>>> 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&amp;data=05%7C01%7Cchristian.koenig%40amd.com%7C52cd6ca16a3a415b92a708da79a67dec%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637956053232922419%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=hIuH18B10sbVAyS0D4iK6R6WYc%2BZ7mlxGcKdUae%2BW6Y%3D&amp;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.
>>
>> I don't think so, because if user get multiple handles for the same 
>> GEM obj and use drm_gem_prime_handle_to_fd() for those handles
> 
> Mhm, that works? This is illegal and should have been prevented somehow.
> 
> Let me double check the code.
> 
> Thanks for pointing that out,
> Christian.
> 

Thanks for checking it, my test case is a preload library which hooks 
the drmModeSetCrtc(and other APIs) then use drmModeGetFB to extract 
dmafd from fb_id.

> 
>> , the current code would try to add multiple maps to rb:
>> drm_prime_add_buf_handle(buf_1, hdl_1)
>> drm_prime_add_buf_handle(buf_1, hdl_2)
>> ...
>> drm_prime_add_buf_handle(buf_1, hdl_n)
>>
>>>
>>>>
>>>> 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().
>>
>> Well, that obj->dma_buf would be set in 
>> drm_gem_prime_fd_to_handle(create new handle), and cleared when 
>> releasing the latest handle(release handle).
>>
>> So it doesn't cover other handle creating path.
>>
>> For example, a imported dma buf:
>> drm_gem_prime_fd_to_handle <-- we got a handle and obj->dma_buf and 
>> obj->import_attach->dmabuf
>> drm_gem_handle_delete <-- we lost that handle and obj->dma_buf cleared
>> drm_gem_open_ioctl/or getfb* <-- we got a new handle and 
>> obj->import_attach->dmabuf
>> drm_gem_handle_delete <-- we lost that handle and obj->dma_buf is 
>> null, which means rb leaks.

Another way to solve this would be set this obj->dma_buf again in 
drm_gem_prime_handle_to_fd(), which would make sure obj->dma_buf is 
valid in all current paths lead to drm_prime_add_buf_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@...k-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)
>>>>>
>>>>>
>>>>
>>>
>>>
>>
> 
> 

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