Re: Radeon RS780 - BUG: unable to handle kernel NULL pointer dereference

[Markus Trippelsdorf <markus@trippelsdorf.de>]

On Mon, Nov 08, 2010 at 11:29:16PM +0100, Thomas Hellstrom wrote:
> On 11/08/2010 09:53 PM, Jerome Glisse wrote:
> >On Mon, Nov 8, 2010 at 2:02 PM, Markus Trippelsdorf
> ><markus@trippelsdorf.de>  wrote:
> >>On Mon, Nov 08, 2010 at 07:43:02PM +0100, Markus Trippelsdorf wrote:
> >>>On Mon, Nov 08, 2010 at 06:07:37PM +0100, Markus Trippelsdorf wrote:
> >>>>On Mon, Nov 08, 2010 at 06:02:21PM +0100, Markus Trippelsdorf wrote:
> >>>>>I can trigger a kernel crash on my system by simply loading this png
> >>>>>image with firefox:
> >>>>>http://mediaarchive.cern.ch/MediaArchive/Photo/Public/2010/1011251/1011251_01/1011251_01-A4-at-144-dpi.jpg
> >>>>Sorry the above link is wrong, this is the right one (that triggers the
> >>>>crash):
> >>>>http://cdsweb.cern.ch/record/1305179/files/HI-150431-630470-huge.png
> >>>I triggered it a few more times and took the attached picture.
> >>>It points to the BUG() call at drivers/gpu/drm/ttm/ttm_bo.c:1628 .
> >>>(Sorry for the bad picture quality)
> >>And here the same BUG in plaintext (should be a bit easier to read):
> >>
> >>Nov  8 19:28:23 arch kernel: ------------[ cut here ]------------
> >>Nov  8 19:28:23 arch kernel: kernel BUG at drivers/gpu/drm/ttm/ttm_bo.c:1628!
> >>
> >Thomas this bug seems to point to a case where we endup trying adding
> >an entry to
> >same offset in the rb tree for addr_space_mm. After reviewing
> >carefully the locking
> >around the rb tree modification&  addr_space_mm i am fairly confident
> >that no race can
> >occur. Would you have any idea on what might go wrong here ? I guess i would
> >ultimately need to dump mm&  rb tree state when BUG get trigger to try
> >to understand
> >states of things.
> 
> I agree there shouldn't be a race in this case.
> The locking around these operations is simple and straightforward.
> 
> So this IMHO should either be a memory corruption or a bug in the
> range manager. I've never seen this BUG trigger before. Dumping mm /
> rb tree contents or bisecting should probably find the culprit.

OK I've found the buggy commit by bisection:

e376573f7267390f4e1bdc552564b6fb913bce76 is the first bad commit                                                                                     
commit e376573f7267390f4e1bdc552564b6fb913bce76                                                                                                      
Author: Michel Dänzer <daenzer@vmware.com>                                                                                                           
Date:   Thu Jul 8 12:43:28 2010 +1000                                                                                                                
                                                                                                                                                     
    drm/radeon: fall back to GTT if bo creation/validation in VRAM fails.                                                                            
                                                                                                                                                     
    This fixes a problem where on low VRAM cards we'd run out of space for validation.                                                               
                                                                                                                                                     
    [airlied: Tested on my M7, Thinkpad T42, compiz works with no problems.]                                                                         
                                                                                                                                                     
    Signed-off-by: Michel Dänzer <daenzer@vmware.com>                                                                                                
    Cc: stable@kernel.org                                                                                                                            
    Signed-off-by: Dave Airlie <airlied@redhat.com> 

Please note that this is an old commit from 2.6.36-rc. When I revert it the
kernel no longer crashes. Instead I see the following in my dmesg:

[TTM] Failed to find memory space for buffer 0xffff880113e10e48 eviction.
[TTM] No space for ffff880113e10e48 (25650 pages, 102600K, 100M)
[TTM]   placement[0]=0x00070002 (1)
[TTM]     has_type: 1
[TTM]     use_type: 1
[TTM]     flags: 0x0000000A
[TTM]     gpu_offset: 0xA0000000
[TTM]     size: 131072
[TTM]     available_caching: 0x00070000
[TTM]     default_caching: 0x00010000
[TTM]  0x00000000-0x00000001:        1: used
[TTM]  0x00000001-0x00000011:       16: used
[TTM]  0x00000011-0x00000111:      256: used
[TTM]  0x00000111-0x00000211:      256: used
[TTM]  0x00000211-0x00000248:       55: free
[TTM]  0x00000248-0x0000024c:        4: used
[TTM]  0x0000024c-0x00001976:     5930: free
[TTM]  0x00001976-0x000021aa:     2100: used
[TTM]  0x000021aa-0x0000285f:     1717: free
[TTM]  0x0000285f-0x00002860:        1: used
[TTM]  0x00002860-0x00002873:       19: free
[TTM]  0x00002873-0x000029b3:      320: used
[TTM]  0x000029b3-0x00020000:   120397: free
[TTM]  total: 131072, used 2954 free 128118
[drm:radeon_cs_ioctl] *ERROR* Failed to parse relocation -12!
radeon 0000:01:05.0: object_init failed for (117555200, 0x00000004)
[drm:radeon_gem_object_create] *ERROR* Failed to allocate GEM object (117555200, 4, 4096, -12)
radeon 0000:01:05.0: object_init failed for (117555200, 0x00000004)
[drm:radeon_gem_object_create] *ERROR* Failed to allocate GEM object (117555200, 4, 4096, -12)
radeon 0000:01:05.0: object_init failed for (117555200, 0x00000004)
[drm:radeon_gem_object_create] *ERROR* Failed to allocate GEM object (117555200, 4, 4096, -12)
radeon 0000:01:05.0: object_init failed for (117555200, 0x00000004)
[drm:radeon_gem_object_create] *ERROR* Failed to allocate GEM object (117555200, 4, 4096, -12)
radeon 0000:01:05.0: object_init failed for (117555200, 0x00000004)
...

And the following in the xorg log buffer:

Failed to alloc memory
Failed to allocat:
   size:     : 117555200 bytes
   alignment : 0 bytes
   domains   : 4
...

-- 
Markus