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SubjectRe: [BUG] 3.4.109 - unable to handle kernel NULL pointer dereference at (null)
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(back from vacation)

On 2015/10/4 12:26, Cal Peake wrote:
> On Thu, 1 Oct 2015, Steven Rostedt wrote:
>
>>
>> I merged 3.4.109 into 3.4-rt, and it bugged. I then booted 3.4.109
>> vanilla and it bugged too. 3.4.108 is fine.
>>
>

I guess this is caused by the following commit, which has already been
reverted in mainline kernel. I'll fix it in 3.4.110.

drm/i915: Don't skip request retirement if the active list is empty
commit 0aedb1626566efd72b369c01992ee7413c82a0c5 upstream.

> I'm getting a similar type bug here. I've bisected it down to this commit:
>
> commit 961bd13539b9e7ca5d2e667668141496b7a1d6bc
> Author: Michel Dänzer <michel.daenzer@amd.com>
> Date: Thu Apr 16 11:17:27 2015 +0900
>
> drm/radeon: Use drm_calloc_ab for CS relocs
>
> commit b421ed15d2c3039eb724680e4de1e4b2bd196a9a upstream.
>
> The number of relocs is passed in by userspace and can be large. It has
> been observed to cause kcalloc failures in the wild.
>
>
> Backing it out of vanilla 3.4.109 has so far eliminated the problem.
>

As you and Satoshi-san have already found out the culprit, I'll just revert
it in 3.4.110.

There are other 2 commits in drivers/gpu/drm/radeon betwwen 3.4.108 and 3.4.109,
and "drm/radeon: fix VM_CONTEXT*_PAGE_TABLE_END_ADDR handling" has been partially
reverted in mainline kernel, so I'll fix this too.

> Steven, you look to be using i915 graphics instead of radeon, so it seems
> unlikely to me that we're hitting the same problem. Here's my oops for
> comparison though:
>
...
> [<ffffffff810d4b93>] ? do_select+0x333/0x5f0
> [<ffffffffa03d90b2>] ? r600_cs_packet_parse+0x42/0x140 [radeon]
> [<ffffffff810d4500>] ? __pollwait+0x110/0x110
> Oct 3 23:24:38 lancer last message repeated 7 times
> [<ffffffff810ba216>] ? kmem_cache_free+0x86/0x90
> [<ffffffff81038d92>] ? __dequeue_signal+0x102/0x190
> [<ffffffff810d505c>] ? core_sys_select+0x20c/0x380
> [<ffffffff8103b608>] ? set_current_blocked+0x38/0x60
> [<ffffffff8103b6ec>] ? block_sigmask+0x3c/0x50
> [<ffffffff81001c84>] ? do_signal+0x1d4/0x620
> [<ffffffff8105b1ad>] ? ktime_get_ts+0x6d/0xe0
> [<ffffffff810d5212>] ? sys_select+0x42/0x110
> [<ffffffff81288982>] ? system_call_fastpath+0x16/0x1b



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