HDLCD crashes with 6d910bfa809e

[liviu.dudau at arm.com]

On Wed, Jun 08, 2016 at 08:58:33AM +0200, Marek Szyprowski wrote:
> Hi All,

Hi Marek,

> 
> 
> On 2016-06-07 16:34, liviu.dudau at arm.com wrote:
> >On Tue, Jun 07, 2016 at 03:11:14PM +0100, Robin Murphy wrote:
> >>Hi Liviu,
> >>
> >>On 07/06/16 14:35, liviu.dudau at arm.com wrote:
> >>>On Tue, Jun 07, 2016 at 01:06:00PM +0100, Robin Murphy wrote:
> >>>>Having just inadvertently merged -next into my working branch, I find
> >>>>dev6d910bfa809e ("drm/hlcd: Use lockless gem BO free callback") adversely
> >>>>affecting my board's ability to boot ;)
> >>>>
> >>>>Since I (intentionally) don't have sufficient CMA to create a framebuffer,
> >>>>drm_gem_cma_create() fails, unconditionally calls the now-NULL
> >>>>drm->driver->gem_free_object() in its cleanup path, and fiery death
> >>>>ensues...
> >>>Thanks for reporting this. What other changes other than reducing the CMA
> >>>allocation size do you have that I might need in order to reproduce this?
> >>I've just confirmed a plain checkout of next-20160602, using arm64 defconfig
> >>+ DRM + HDLCD + TDA998X and CMA_SIZE_MBYTES=1, booted on a Juno, does the
> >>job:
> >>
> >>[    3.032402] hdlcd 7ff60000.hdlcd: bound 0-0070 (ops tda998x_ops)
> >>[    3.038388] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
> >>[    3.044970] [drm] No driver support for vblank timestamp query.
> >>[    3.076973] hdlcd 7ff60000.hdlcd: failed to allocate buffer with size
> >>7680000
> >>[    3.084081] Bad mode in Synchronous Abort handler detected, code
> >>0x86000004 -- IABT (current EL)
> >>[    3.092815] CPU: 3 PID: 6 Comm: kworker/u12:0 Not tainted
> >>4.7.0-rc1-next-20160602 #686
> >>[    3.100682] Hardware name: ARM Juno development board (r1) (DT)
> >>[    3.106567] Workqueue: deferwq deferred_probe_work_func
> >>[    3.111761] task: ffff8009768a3e80 ti: ffff8009768e8000 task.ti:
> >>ffff8009768e8000
> >>[    3.119198] PC is at 0x0
> >>[    3.121720] LR is at drm_gem_cma_create+0x128/0x130
> >>...and so on.
> >>
> >>Today's -next, on the other hand, dodges the bullet entirely:
> >>
> >>[    2.903645] [drm] found ARM HDLCD version r0p0
> >>[    2.908122] hdlcd 7ff60000.hdlcd: master bind failed: -22
> >>[    2.913505] tda998x: probe of 0-0070 failed with error -22
> >>[    2.919141] [drm] found ARM HDLCD version r0p0
> >>[    2.923609] hdlcd 7ff50000.hdlcd: master bind failed: -22
> >>[    2.928991] tda998x: probe of 0-0071 failed with error -22
> >OK, the problem is that commit 59ce4039727ef40 has changed the behaviour from when
> >there is no "memory-region" phandle in the DT: before it used to return -ENODEV, now
> >it returns -EINVAL.
> >
> >Marek, I quite liked the old behaviour to detect if the DT had the optional (from
> >my driver's point of view) "memory-region" phandle. Plus the check for dev is superfluous
> >when using of_reserved_mem_device_init() as that uses dev->of_node for np so it would
> >crash before the check anyway. Maybe move the check there?
> >
> >Until then I suggest reverting the 59ce4039727ef40 commit.
> 
> I've just send a fix for this issue. I'm sorry for the regression. I hope
> the fix fill
> quickly get into next to solve your problem.

Thanks for the patch, however I have some comments to it.

> 
> The additional check for null dev make sense, because the new function
> of_reserved_mem_device_init_by_idx can be called with any device and node
> pointer not
> embedded with it, so I would like to keep it safe.

And I have to admit I find that scary. Why do you accept any node that is *not* related to
the device? If you want just the ability to parse multiple "memory-region" phandles (where
are the bindings defined for that?) I would have modified of_reserved_mem_device_init() to
the the parsing and accept either the single entry style or a node with multiple
"memory-region" phandles in it. Otherwise I can steal the "memory-region" of another device
and that device would have no idea that I have done this.

Can you point me to the latest thread where this patch has been discussed?

Best regards,
Liviu

> 
> Best regards
> -- 
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
> 

-- 
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