linux-kernel - Re: [PATCH AUTOSEL 5.10 13/22] drm/amdgpu: install stub fence into potential unused fence pointers

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Date:   Fri, 1 Sep 2023 08:02:18 +0200
From:   Christian König <ckoenig.leichtzumerken@...il.com>
To:     Chia-I Wu <olvaffe@...il.com>, Greg KH <gregkh@...uxfoundation.org>
Cc:     Sasha Levin <sashal@...nel.org>, airlied@...ux.ie,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org,
        Alex Deucher <alexander.deucher@....com>,
        stable@...r.kernel.org, Lang Yu <Lang.Yu@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH AUTOSEL 5.10 13/22] drm/amdgpu: install stub fence into
 potential unused fence pointers

Am 31.08.23 um 20:55 schrieb Chia-I Wu:
> On Thu, Aug 31, 2023 at 7:01 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>> On Thu, Aug 31, 2023 at 03:26:28PM +0200, Christian König wrote:
>>> Am 31.08.23 um 12:56 schrieb Greg KH:
>>>> On Thu, Aug 31, 2023 at 12:27:27PM +0200, Christian König wrote:
>>>>> Am 30.08.23 um 20:53 schrieb Chia-I Wu:
>>>>>> On Sun, Jul 23, 2023 at 6:24 PM Sasha Levin <sashal@...nel.org> wrote:
>>>>>>> From: Lang Yu <Lang.Yu@....com>
>>>>>>>
>>>>>>> [ Upstream commit 187916e6ed9d0c3b3abc27429f7a5f8c936bd1f0 ]
>>>>>>>
>>>>>>> When using cpu to update page tables, vm update fences are unused.
>>>>>>> Install stub fence into these fence pointers instead of NULL
>>>>>>> to avoid NULL dereference when calling dma_fence_wait() on them.
>>>>>>>
>>>>>>> Suggested-by: Christian König <christian.koenig@....com>
>>>>>>> Signed-off-by: Lang Yu <Lang.Yu@....com>
>>>>>>> Reviewed-by: Christian König <christian.koenig@....com>
>>>>>>> Signed-off-by: Alex Deucher <alexander.deucher@....com>
>>>>>>> Signed-off-by: Sasha Levin <sashal@...nel.org>
>>>>>>> ---
>>>>>>>     drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 6 ++++--
>>>>>>>     1 file changed, 4 insertions(+), 2 deletions(-)
>>>>>> We start getting this warning spew on chromeos
>>>>> Yeah because the older kernels still kept track of the last VM fence in the
>>>>> syncobj.
>>>>>
>>>>> This patch here should probably not have been back ported.
>>>>>
>>>>> Why was that done anyway? The upstream commit doesn't have a CC stable and
>>>>> this is only a bug fix for a new feature not present on older kernels.
>>>> It is part of the AUTOSEL process.
>>> Could we prevent patches from being backported by adding a Fixes: tag?
>> Yes, that will show exactly where the patch should be backported to.
> This is also AUTOSEL'ed to 5.15.  That might need a revert as well,
> depending on when the amdgpu feature landed.

Both the feature and the bug fix landed in 6.5.

The bug fix should have never been backported to any older kernel at all 
as far as I can see.

Regards,
Christian.

>
>
>> thanks,
>>
>> greg k-h