[REGRESSION] Re: i915 driver crashes on T540p if docking station attached

[Theodore Ts'o]

On Wed, Jul 29, 2015 at 08:49:37PM -0400, Theodore Ts'o wrote:
> 
> Unfortunately the failure causes a series of recursive faults and I
> haven't been able to capture the stack trace, but on 4.2-rcX kernels,
> I can reliably cause the system to crash if my T540p is booted with
> the docking station attached.
> 
> It will also crash if I boot the system first, and then insert the
> laptop into the dockstation.
> 
> Unfortunately, I can't get a stack trace because there are a huge
> number of recursive/double faults, and the system dies so quickly that
> nothing ends up in the log files.  If you really need a stack dump I
> can try to rig something, but modern Laptops don't have serial
> consoles any more, alas, so it's bit of a pain.

The bad news is that I tried to use kdump to capture a crashdump and
hopefully get more information, and kdump utterly wedged on the panic.
The good news is because it wedged the system, I was able to get the
console stackdump before it scrolled off due to a whole series of
recursive oops messages.

It's here:  https://goo.gl/photos/xHjn2Z97JQEw6k2C9

Hopefully tihs is useful.  It's not obvious how to revert this change,
since there were a large number of changes to i915 after this.  If
someone could help me with a revert, I'd be happy to test it.

Thanks,

						- Ted
						


> 
> I was able to bisect it down to this commit, however: 8c7b5ccb72987:
> "drm/i915: Use atomic helpers for computing changed flags:"
> 
> Is there any chance Intel could add a Lenovo Dockstation with a
> Multistream DP output to part of your test hardware?  Unfortunately it
> seems pretty common that I see regressions with my particular
> hardware.  Maybe there aren't enough people using Thinkpads any more?  :-(
> 
>       	     	    	   	 	       	      - Ted
> 
> 
> P.S.  The git bisect log
> 
> git bisect start
> # bad: [421d125c06c4be4c5005cb69840206bd09b71dd6] builddeb: sign the modules after splitting out the debuginfo files
> git bisect bad 421d125c06c4be4c5005cb69840206bd09b71dd6
> # good: [b953c0d234bc72e8489d3bf51a276c5c4ec85345] Linux 4.1
> git bisect good b953c0d234bc72e8489d3bf51a276c5c4ec85345
> # good: [aeaa2122af4e53f3bfd28e8f294557bb95af43fc] drm/i915/skl: Add the INIT power domain to the MISC I/O power well
> git bisect good aeaa2122af4e53f3bfd28e8f294557bb95af43fc
> # bad: [4d70f38a760ad2879d2ebd84001c92980180f630] drm/i915/bios: remove a redundant NULL pointer check
> git bisect bad 4d70f38a760ad2879d2ebd84001c92980180f630
> # bad: [27a1b688d9f1fa2abd14bfe6a8729a19fb3b1b25] drm/i915/bxt: Enable WaEnableYV12BugFixInHalfSliceChicken7 for Broxton
> git bisect bad 27a1b688d9f1fa2abd14bfe6a8729a19fb3b1b25
> # good: [4be0731786de10d0e9ae1d159504c83c6b052647] drm/i915: Add crtc states before calling compute_config()
> git bisect good 4be0731786de10d0e9ae1d159504c83c6b052647
> # good: [d5432a9d19b61ba6a2b3d88f3026e0ca60eb57a1] drm/i915: Stage new modeset state straight into atomic state
> git bisect good d5432a9d19b61ba6a2b3d88f3026e0ca60eb57a1
> # bad: [a821fc46bc7bb6d4cf9a5f8d2787fd70231c2c10] drm/i915: Swap atomic state in legacy modeset
> git bisect bad a821fc46bc7bb6d4cf9a5f8d2787fd70231c2c10
> # bad: [8c7b5ccb729870e606321b3703e2c2e698c49a95] drm/i915: Use atomic helpers for computing changed flags
> git bisect bad 8c7b5ccb729870e606321b3703e2c2e698c49a95
> # good: [0f63cca2afdc38877e86acfa9821020f6e2213fd] drm/i915: Update crtc state active flag based on DPMS
> git bisect good 0f63cca2afdc38877e86acfa9821020f6e2213fd
> # good: [840bfe953384a134c8639f2964d9b74bfa671e16] drm/atomic: Make mode_fixup() optional for check_modeset()
> git bisect good 840bfe953384a134c8639f2964d9b74bfa671e16
> # first bad commit: [8c7b5ccb729870e606321b3703e2c2e698c49a95] drm/i915: Use atomic helpers for computing changed flags
> 
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