laptop suspend broken after latest kernel update

I ran a software update (Ubuntu 14.04) on my laptop over the weekend, which included an update from kernel 3.13.0-24 to 3.13.0-27, among other things. Today i had to take my laptop to work, so closed the lid and put it in my bag. However, it never went into suspend mode! I tried several times, even rebooting. Finally I tried the previous kernel from the grub menu (reverting back to the -24 one) and suspend works the same as it always had before.

Did something suspend related change between the -24 and -27 kernels used in Ubuntu 14.04? I think by only reverting to a previous kernel to temporarily fix it, i've ruled out any other software changes made during the weekend's upgrade.

EDIT: I've compared my syslog after an unsuccessful suspend with the results with the working kernel, and here's where they differ:

After these lines which appear in both logs,

May 28 13:44:20 inanna kernel: [  559.606085] nouveau  [     DRM] suspending client object trees...
May 28 13:44:20 inanna kernel: [  559.607177] nouveau  [     DRM] suspending kernel object tree...

the non-working suspend continues with

May 28 13:44:20 inanna kernel: [  561.606427] nouveau E[   PDISP][0000:01:00.0][0xc000857c][ffff880035a4af80] fini timeout, 0xc2061008
May 28 13:44:20 inanna kernel: [  561.606429] nouveau E[   PDISP][0000:01:00.0][0xc000857c][ffff880035a4af80] failed suspend, -16
May 28 13:44:20 inanna kernel: [  561.606430] nouveau E[     DRM] 0xd1500000:0xd15c7c00 suspend failed with -16
May 28 13:44:20 inanna kernel: [  561.606447] nouveau E[     DRM] 0xdddddddd:0xd1500000 suspend failed with -16
May 28 13:44:20 inanna kernel: [  561.606535] nouveau E[     DRM] 0xffffffff:0xdddddddd suspend failed with -16
May 28 13:44:20 inanna kernel: [  561.607173] nouveau E[     DRM] 0xffffffff:0xffffffff suspend failed with -16
May 28 13:44:20 inanna kernel: [  561.607273] nouveau  [     DRM] resuming display...
May 28 13:44:20 inanna kernel: [  561.607294] nouveau E[     DRM] bo ffff880092b8bc00 pinned elsewhere: 0x00000002 vs 0x00000004
May 28 13:44:20 inanna kernel: [  561.607295] [drm:drm_helper_resume_force_mode] *ERROR* failed to set mode on crtc ffff88024e006000
May 28 13:44:20 inanna kernel: [  561.607324] pci_pm_suspend(): nouveau_pmops_suspend+0x0/0xb0 [nouveau] returns -16
May 28 13:44:20 inanna kernel: [  561.607327] dpm_run_callback(): pci_pm_suspend+0x0/0x150 returns -16
May 28 13:44:20 inanna kernel: [  561.607329] PM: Device 0000:01:00.0 failed to suspend async: error -16
May 28 13:44:20 inanna kernel: [  561.607485] PM: Some devices failed to suspend, or early wake event detected

I'm afraid we/you have very few options at the moment. We/You most probably suffer from Bug 1324697.

One of the workarounds is to use the kernel 3.13.0-24, as you already stated. The other is to use one of the mainline kernels of the kernel ppa. I chose the 3.16.0-031600 version.