Re: Oops in 3.10.99 -- NULL pointer dereference in radeon_fence_ref

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

Am 07.03.2016 um 21:46 schrieb Greg Kroah-Hartman:
> On Sun, Mar 06, 2016 at 07:50:14PM -0700, Erik Andersen wrote:
>> The following patch to radeon_sa_bo_new that
>> went into 3.10.99
>>
>>    commit 8d5e1e5af0c667545c202e8f4051f77aa3bf31b7
>>    Author: Nicolai Hähnle <nicolai.haehnle@amd.com>
>>    Date:   Fri Feb 5 14:35:53 2016 -0500
>>      drm/radeon: hold reference to fences in radeon_sa_bo_new
>>      commit f6ff4f67cdf8455d0a4226eeeaf5af17c37d05eb upstream.
>>
>> is triggering an Oops for me right when xscreensaver
>> first began doing 3D stuff.  After reverting this
>> patch, xscreensaver has been happily running 3D stuff.
>>
>> Mar  6 18:00:43 sage kernel: BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
>> Mar  6 18:00:43 sage kernel: IP: [<ffffffffa010345d>] radeon_fence_ref+0xd/0x50 [radeon]
>> Mar  6 18:00:43 sage kernel: PGD 799e1d067 PUD 819186067 PMD 0
>> Mar  6 18:00:43 sage kernel: Oops: 0002 [#1] SMP
>>
>> Mar  6 18:00:43 sage kernel: Stack:
>> Mar  6 18:00:43 sage kernel:  ffffffffa01607ec ffff88108a4e8000 ffff88108a4e8000 ffff880888fbc000
>> Mar  6 18:00:43 sage kernel:  ffff880ecbf11c78 0000fe2001000006 0000000000000000 0020000000000100
>> Mar  6 18:00:43 sage kernel:  00000000000d1200 ffff880ecbf11c14 0000000000000000 0000000000000000
>> Mar  6 18:00:43 sage kernel: Call Trace:
>> Mar  6 18:00:43 sage kernel:  [<ffffffffa01607ec>] ? radeon_sa_bo_new+0x2ac/0x4f0 [radeon]
>> Mar  6 18:00:43 sage kernel:  [<ffffffffa005fc9d>] ? ttm_eu_list_ref_sub+0x3d/0x60 [ttm]
>> Mar  6 18:00:43 sage kernel:  [<ffffffffa0117c49>] radeon_ib_get+0x39/0x110 [radeon]
>> Mar  6 18:00:43 sage kernel:  [<ffffffffa011a4ea>] radeon_cs_ioctl+0x69a/0xa70 [radeon]
>> Mar  6 18:00:43 sage kernel:  [<ffffffffa008e2d2>] drm_ioctl+0x512/0x650 [drm]
>> Mar  6 18:00:43 sage kernel:  [<ffffffff810a46e1>] ? do_futex+0x111/0xc30
>> Mar  6 18:00:43 sage kernel:  [<ffffffff81182a45>] do_vfs_ioctl+0x305/0x520
>> Mar  6 18:00:43 sage kernel:  [<ffffffff8107cd39>] ? vtime_account_user+0x69/0x80
>> Mar  6 18:00:43 sage kernel:  [<ffffffff81182ce1>] SyS_ioctl+0x81/0xa0
>> Mar  6 18:00:43 sage kernel:  [<ffffffff8178210f>] tracesys+0xe1/0xe6
>>
>> $ lspci | grep VGA
>> 03:00.0 VGA compatible controller: Advanced Micro Devices, Inc.
>> [AMD/ATI] Redwood XT [Radeon HD 5670/5690/5730]
> Next time, please cc: the people responsible for that patch as well...
>
> I can revert it, but maybe something else is going on here?  Do you have
> this same problem on 3.14, and 4.5-rc7?

Hi Greg,

yes that's an already known issue. Feel free to revert that one for now.

I got it on my TODO list to provide a fixed patch for older kernel, but 
that can take a while.

For the background Nicolais patch is correct, but assumes that 
radeon_fence_unref() can safely take NULL as the fence which is not the 
case for older kernels.

Regards,
Christian.

>
> thanks,
>
> greg k-h