Chrome Version 44.0.2403.125 (64-bit) on ubuntu with 
libdrm-2.4.60, libdrm-2.4.56 and Peter Hurley's libdrm-2.4.60 with the fix applied for this bug : https://bugs.freedesktop.org/show_bug.cgi?id=89842#c19 can cause the kernel driver to reject validation of a push_buffer from the nouveau push_buffer logic in nouveau_pushbuf_kick, leading to the following message

nouveau E[chrome[2737]] multiple instances of buffer 33 on validation list 
nouveau E[chrome[2737]] validate_init 
nouveau E[chrome[2737]] validate: -22 
nouveau E[chrome[2737]] multiple instances of buffer 18 on validation list 
nouveau E[chrome[2737]] validate_init 
nouveau E[chrome[2737]] validate: -22 
nouveau E[ PFIFO][0000:01:00.0] PFIFO: read fault at 
0x0003e21000 [PAGE_NOT_PRESENT] from (unknown enum 
0x00000000)/GPC0/(unknown enum 0x0000000f) on channel 0x007f80c000 
[unknown] 

The following work-around works for me on Linux 4.2-rc4

http://www.gossamer-threads.com/lists/linux/kernel/2228405

Where I tell the kernel to 'continue' if it already has mapped memory specified in a push buffer for a given PID.

Using that work-around means I still get the 'multiple instances' error message but, it's not treated as fatal and so far has been completely stable for me.

The feedback from LKML was that this is probably a bug in libdrm.

I've downloaded and run the test associated with bug 89842 i.e. libdrm-2.4.60/tests/nouveau/threaded.c using various versions of libdrm2 as suggested on LKML and I can confirm that the race condition the test tests for is not present.

Launchpad PPA @ ppa:phurley/libdrm - 2.4.60 with bugfix 89842 applied does not fault on the threaded test libdrm-2.4.60/tests/nouveau/threaded.c but does get into a 'multiple instances' state on the nouveau push_buf list - again on the stock ubuntu kernel and the tip-of-tree 4.2-rcX

deckard@aineko:~/Development/nouveau/libdrm-2.4.60$ dpkg -s libdrm2
Package: libdrm2
Status: install ok installed
Priority: optional
Section: libs
Installed-Size: 106
Maintainer: Debian X Strike Force <debian-x@lists.debian.org>
Architecture: amd64
Multi-Arch: same
Source: libdrm
Version: 2.4.60-2ppa1~trusty1
Depends: libc6 (>= 2.17)
Pre-Depends: multiarch-support
Description: Userspace interface to kernel DRM services -- runtime
 This library implements the userspace interface to the kernel DRM
 services.  DRM stands for "Direct Rendering Manager", which is the
 kernelspace portion of the "Direct Rendering Infrastructure" (DRI).
 The DRI is currently used on Linux to provide hardware-accelerated
 OpenGL drivers.
 .
 This package provides the runtime environment for libdrm.

deckard@aineko:~/Development/nouveau/libdrm-2.4.60$ uname -a
Linux aineko 4.2.0-rc4+ #50 SMP Thu Jul 30 01:22:01 IST 2015 x86_64 x86_64 x86_64 GNU/Linux

Chrome Version 44.0.2403.125 (64-bit)

Steps to replicate:

Run the version of chrome indicated above. Open a number of tabs to different websites. Click on the horizontal bars in the top right to get the drop-down menu, and hover the cursor over bookmarks or recent tabs.

This process is a bit hit and miss and make take a unknown number of tabs/time to elicit the behaviour, sorry I can't be more concise at this point.

It's not clear if bug 89842 will fix all or some of the issues reported in this Ubuntu thread : http://tinyurl.com/orvbzf3 but, I've verified the test program developed to debug that race condition doesn't cause a mjultiple instances message on my machine.

2014 Macbook pro - running bunutu 14.04, issue is present with stock ubuntu kernel and the 4.2-rcX kernel I'm using to debug this issue.

01:00.0 VGA compatible controller: NVIDIA Corporation GK107M [GeForce GT 750M Mac Edition] (rev a1) (prog-if 00 [VGA controller])
	Subsystem: Apple Inc. Device 0130
	Flags: bus master, fast devsel, latency 0, IRQ 45
	Memory at c0000000 (32-bit, non-prefetchable) [size=16M]
	Memory at 80000000 (64-bit, prefetchable) [size=256M]
	Memory at 90000000 (64-bit, prefetchable) [size=32M]
	I/O ports at 1000 [size=128]
	Expansion ROM at c1000000 [disabled] [size=512K]
	Capabilities: [60] Power Management version 3
	Capabilities: [68] MSI: Enable+ Count=1/1 Maskable- 64bit+
	Capabilities: [78] Express Endpoint, MSI 00
	Capabilities: [b4] Vendor Specific Information: Len=14 <?>
	Capabilities: [100] Virtual Channel
	Capabilities: [128] Power Budgeting <?>
	Capabilities: [420] Advanced Error Reporting
	Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 <?>
	Capabilities: [900] #19
	Kernel driver in use: nouveau

01:00.1 Audio device: NVIDIA Corporation GK107 HDMI Audio Controller (rev a1)
	Subsystem: Apple Inc. Device 0130
	Flags: bus master, fast devsel, latency 0, IRQ 17
	Memory at c1080000 (32-bit, non-prefetchable) [size=16K]
	Capabilities: [60] Power Management version 3
	Capabilities: [68] MSI: Enable- Count=1/1 Maskable- 64bit+
	Capabilities: [78] Express Endpoint, MSI 00
	Kernel driver in use: snd_hda_intel