Hmm. I suspect it's more than a coincidence that it's a single bit flipped.

The same bitflip is back :D

https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_4265/shard-glk8/igt@gem_tiled_blits@interruptible.html

(gem_tiled_blits:2600) CRITICAL: Test assertion failure function check_bo, file ../tests/gem_tiled_blits.c:110:
(gem_tiled_blits:2600) CRITICAL: Failed assertion: linear[i] == start_val
(gem_tiled_blits:2600) CRITICAL: Last errno: 1, Operation not permitted
(gem_tiled_blits:2600) CRITICAL: Expected 0x2cf222a8, found 0x2ef222a8 at offset 0x00088aa0
Subtest interruptible failed.

I mean, it is the same bit, but not the same direction.

Pushed commit 8a8f0271a71e2e0d2a2caa4d41f4ad1d9c89670e (HEAD, upstream/master)
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Thu May 31 18:19:45 2018 +0100

    igt/gem_tiled_blits: Show more errors
    
    glk is failing gem_tiled_blits which is very odd as it doesn't use
    fencing and so the tiling is all internal to the GPU. From the small
    number of examples seen so far, it looks like just a single bit is being
    flipped. Let's dump some values to see if it there is a larger pattern
    here.
    
    Furthermore since gem_linear_blits is also showing bitflips on glk, we
    can rule out the impact of tiling altogether! It just becomes a question
    of which piece of hw is broken...
    
    References: https://bugs.freedesktop.org/show_bug.cgi?id=106608
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
    Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

to see if the pattern holds.

(In reply to Chris Wilson from comment #4)
> Pushed commit 8a8f0271a71e2e0d2a2caa4d41f4ad1d9c89670e (HEAD,
> upstream/master)
> Author: Chris Wilson <chris@chris-wilson.co.uk>
> Date:   Thu May 31 18:19:45 2018 +0100
> 
>     igt/gem_tiled_blits: Show more errors
>     
>     glk is failing gem_tiled_blits which is very odd as it doesn't use
>     fencing and so the tiling is all internal to the GPU. From the small
>     number of examples seen so far, it looks like just a single bit is being
>     flipped. Let's dump some values to see if it there is a larger pattern
>     here.
>     
>     Furthermore since gem_linear_blits is also showing bitflips on glk, we
>     can rule out the impact of tiling altogether! It just becomes a question
>     of which piece of hw is broken...
>     
>     References: https://bugs.freedesktop.org/show_bug.cgi?id=106608
>     Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>     Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> 
> to see if the pattern holds.

Now this bug has been shy and not shown itself in over 5 months. Let's close it!