How to fix Retina iMac "A graphics problem has been detected”?

I'm having a problem with my Retina iMac regularly generating a "A graphics problem has been detected" error. The iMac has the AMD Radeon R9 M295X option.

At the end of the day I walk away from it and leave it to its own devices. I don't power it down or explicitly put it to sleep. In the morning I expect to wake it up and carry on, but it often needs to be powered on and boot up.

When it reboots I see a dialog with the "A graphics problem has been detected" error message.

In the console log I see a series of "Trying restart GPU" messages". Below is the last of these messages and all the log entries before.

Anyone know how to fix this?

21/12/14 3:52:44.000 am kernel[0]: Trying restart GPU ...
21/12/14 3:52:44.905 am com.apple.xpc.launchd[1]: (com.apple.DumpGPURestart) Service only ran for 8 seconds. Pushing respawn out by 2 seconds.
21/12/14 3:52:46.919 am DumpGPURestart[1410]: Saved gpuRestart report for kernel to /Library/Logs/DiagnosticReports/Kernel_2014-12-21-035246_newton.gpuRestart
21/12/14 3:52:53.000 am kernel[0]: [1:0:0] GPU HangState 0x000000c0, HangFlags 0x00000007: IndividualEngineHang 1, NonEngineBlockHang 1, FenceNotRetired 1, PerEngineReset 0, FullAsicReset 1
21/12/14 3:52:54.000 am kernel[0]: 0000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : 0x00000000 : 0x00000000 
21/12/14 3:52:54.000 am kernel[0]: : ** GPU Debug Info End **
21/12/14 3:52:54.000 am kernel[0]: ------------------------
21/12/14 3:52:54.000 am kernel[0]: GPURestartReportEnd
21/12/14 3:52:54.000 am kernel[0]: Trying restart GPU ...
21/12/14 3:52:54.875 am com.apple.xpc.launchd[1]: (com.apple.DumpGPURestart) Service only ran for 7 seconds. Pushing respawn out by 3 seconds.
21/12/14 3:52:57.890 am DumpGPURestart[1411]: Saved gpuRestart report for kernel to /Library/Logs/DiagnosticReports/Kernel_2014-12-21-035257_newton.gpuRestart
21/12/14 3:53:27.298 am apsd[52]: Failed entitlement check 'com.apple.private.aps-connection-initiate' for ManagedClientAgent[1412]
21/12/14 3:53:27.298 am apsd[52]: Peer connection [pid=1412] lacks APSConnectionInitiateEntitlement
21/12/14 3:53:32.299 am ManagedClientAgent[1412]: No Device Enrollment record info was found
21/12/14 3:56:05.000 am kernel[0]: PM priority notification timeout
21/12/14 3:56:06.000 am kernel[0]: hibernate image path: /var/vm/sleepimage
21/12/14 3:56:06.000 am kernel[0]: efi pagecount 67
21/12/14 3:56:06.000 am kernel[0]: hibernate_page_list_setall(preflight 1) start 0xffffff82114d5000, 0xffffff8211555000
21/12/14 3:56:06.000 am kernel[0]: hibernate_page_list_setall time: 569 ms
21/12/14 3:56:06.000 am kernel[0]: pages 3753650, wire 316199, act 1921147, inact 20159, cleaned 0 spec 13, zf 55501, throt 0, compr 0, xpmapped 0
21/12/14 3:56:06.000 am kernel[0]: could discard act 560471 inact 405794 purgeable 211784 spec 262582 cleaned 0
21/12/14 3:56:06.000 am kernel[0]: hibernate_page_list_setall preflight pageCount 316199 est comp 50 setfile 836763648 min 2147483648
21/12/14 3:56:06.000 am kernel[0]: AppleThunderboltNHIType2::prePCIWake - power up complete - took 2 us
21/12/14 3:56:06.000 am kernel[0]: AppleThunderboltGenericHAL::earlyWake - complete - took 0 milliseconds
21/12/14 3:56:06.000 am kernel[0]: [0x59c815000, 0x40000000]
21/12/14 3:56:06.000 am kernel[0]: [0x5dc815000, 0x40000000]
21/12/14 3:56:06.000 am kernel[0]: [0x0, 0x0]
21/12/14 3:56:06.000 am kernel[0]: kern_open_file_for_direct_io(0) took 4 ms
21/12/14 3:56:06.000 am kernel[0]: Opened file /var/vm/sleepimage, size 2147483648, partition base 0x0, maxio 2000000 ssd 1
21/12/14 3:56:06.000 am kernel[0]: hibernate image major 1, minor 0, blocksize 4096, pollers 5