Ubuntu Wily / VMWare graphics boot regression

[Kamal Mostafa]

On Thu, 2016-02-25 at 09:46 +0100, Thomas Hellstrom wrote:
> Hi!
> 
> There is a fix for this problem already upstream. For some reason it
> wasn't cc'd stable..
> The commit id is
> 
> 12617971c443c50750a12a77ea0e08319d161975
> 
> and it applies from 3.15 to 4.2 provided the ttm fix is applied.
> 
> I'll send a message through stable.
> 
> /Thomas


Confirmed.  This does indeed fix:

  https://bugs.launchpad.net/ubuntu/wily/+source/linux/+bug/1548587
  Ubuntu 15.10 VMWare guest won't show UI after upgrading to 4.2.0-30

Thanks Thomas!

 -Kamal


> 
> On 02/25/2016 07:13 AM, Thomas Hellstrom wrote:
> > Hi!
> > 
> > Ugh. I'll try to reproduce and see if I can provide a fix. 4.3 saw
> > a
> > major linux modesetting rewrite so it might be possible that we
> > fixed
> > more than one bug and previously they might have canceled out
> > eachother....
> > 
> > /Thomas
> > 
> > 
> > 
> > On 02/25/2016 12:27 AM, Sinclair Yeh wrote:
> > > Hi,
> > > 
> > > I was able to reproduce this last night after updating 15.10, and
> > > I
> > > didn't know what the cause was until your mail.
> > > 
> > > Let me try a 4.2 kernel with lockdep check enabled and see if I
> > > can
> > > spot anything.
> > > 
> > > Thomas' in a different time zone, so he may also pick this up in
> > > his morning.
> > > 
> > > Sinclair
> > > 
> > > On Wed, Feb 24, 2016 at 02:42:10PM -0800, Kamal Mostafa wrote:
> > > > Hi Thomas, Sinclair, and my team-
> > > > 
> > > > Here's a weird one.  It appears that this Linux commit which
> > > > was
> > > > recently applied to Ubuntu Wily 15.10 (via 4.2-stable):
> > > > 
> > > >   [mainline] 025af18 drm/ttm: Fixed a read/write lock imbalance
> > > > 
> > > > is the trigger for this rather major Ubuntu/VMWare graphics
> > > > boot
> > > > regression:
> > > > 
> > > >   https://bugs.launchpad.net/ubuntu/wily/+source/linux/+bug/154
> > > > 8587
> > > >   Ubuntu 15.10 VMWare guest won't show UI after upgrading to
> > > > 4.2.0-30
> > > > 
> > > > (In Comment #33 I produced a test kernel with that commit
> > > > reverted  
> > > > which was confirmed as fixing the regression).
> > > > 
> > > > 
> > > > But the thing is...
> > > > 
> > > > 025af18 (attached) just looks so *obviously* valid, in that the
> > > > thing
> > > > it fixes looks like it was obviously wrong.  I was reluctant to
> > > > even
> > > > try reverting it, and was surprised when multiple testers
> > > > confirmed
> > > > that it fixed the problem.
> > > > 
> > > > Furthermore, backports of 025af18 have been deployed in many
> > > > other
> > > > stable kernels (and of course, mainline) but the reported boot
> > > > problem
> > > > ** only seems to occur with v4.2-based kernels **.  The problem
> > > > does
> > > > occur with 4.2-stable (including the 025af18 backport), but
> > > > does _not_
> > > > occur with a 4.4 kernel (which always contained 025af18).  That
> > > > commit
> > > > been shipping in pre-4.2 Ubuntu Trusty and Vivid for at cycle
> > > > or two
> > > > with no reports of problems there either.
> > > > 
> > > > So despite the indication that 025af18 is the troublemaker for
> > > > 4.2-
> > > > stable based kernels, I'm not very happy with the idea of just
> > > > reverting it from 4.2-stable or from Wily without a better
> > > > understanding of why.
> > > > 
> > > > Any thoughts on this topic will be much appreciated.
> > > > 
> > > >  -Kamal
> > > > From 025af189fb44250206dd8a32fa4a682392af3301 Mon Sep 17
> > > > 00:00:00 2001
> > > > From: Thomas Hellstrom <thellstrom at vmware.com>
> > > > Date: Fri, 20 Nov 2015 11:43:50 -0800
> > > > Subject: drm/ttm: Fixed a read/write lock imbalance
> > > > 
> > > > In ttm_write_lock(), the uninterruptible path should call
> > > > __ttm_write_lock() not __ttm_read_lock().  This fixes a vmwgfx
> > > > hang
> > > > on F23 start up.
> > > > 
> > > > syeh: Extracted this from one of Thomas' internal patches.
> > > > 
> > > > Cc: <stable at vger.kernel.org>
> > > > Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
> > > > Reviewed-by: Sinclair Yeh <syeh at vmware.com>
> > > > ---
> > > >  drivers/gpu/drm/ttm/ttm_lock.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/ttm/ttm_lock.c
> > > > b/drivers/gpu/drm/ttm/ttm_lock.c
> > > > index 6a95454..f154fb1 100644
> > > > --- a/drivers/gpu/drm/ttm/ttm_lock.c
> > > > +++ b/drivers/gpu/drm/ttm/ttm_lock.c
> > > > @@ -180,7 +180,7 @@ int ttm_write_lock(struct ttm_lock *lock,
> > > > bool interruptible)
> > > >  			spin_unlock(&lock->lock);
> > > >  		}
> > > >  	} else
> > > > -		wait_event(lock->queue,
> > > > __ttm_read_lock(lock));
> > > > +		wait_event(lock->queue,
> > > > __ttm_write_lock(lock));
> > > >  
> > > >  	return ret;
> > > >  }