We've also seen this on the -24.38 and -24.39 kernels now:

[56843.390534] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
[56843.390551] IP: [<ffffffff8130d901>] rb_next+0x1/0x50
[56843.390566] PGD 1d20a7067 PUD 1d29a2067 PMD 0 
[56843.390575] Oops: 0000 [#1] SMP 
[56843.390583] CPU 1 
[56843.390585] Modules linked in: ipt_REJECT xt_tcpudp nf_conntrack_ipv4 nf_defrag_ipv4 xt_state nf_conntrack iptable_filter ip_tables x_tables parport_pc ppdev lp parport isofs acpiphp
[56843.390616] 
[56843.390621] Pid: 1340, comm: chef-client Not tainted 3.2.0-24-virtual #39-Ubuntu  
[56843.390629] RIP: e030:[<ffffffff8130d901>]  [<ffffffff8130d901>] rb_next+0x1/0x50
[56843.390638] RSP: e02b:ffff8801d050dc18  EFLAGS: 00010046
[56843.390642] RAX: 0000000000000000 RBX: ffff8801d24c8e00 RCX: 0000000000000000
[56843.390648] RDX: fffffffffffffff0 RSI: 0000000000000000 RDI: 0000000000000010
[56843.390654] RBP: ffff8801d050dc48 R08: 0000000000000000 R09: 0000000000000000
[56843.390659] R10: ffff8801dff866c0 R11: 0000000000000001 R12: 0000000000000000
[56843.390664] R13: 0000000000000000 R14: 0000000000000000 R15: 00000000011168a8
[56843.390674] FS:  00007fda5feaa700(0000) GS:ffff8801dff8f000(0000) knlGS:0000000000000000
[56843.390681] CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
[56843.390686] CR2: 0000000000000010 CR3: 00000001d28cc000 CR4: 0000000000002660
[56843.390692] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[56843.390698] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[56843.390704] Process chef-client (pid: 1340, threadinfo ffff8801d050c000, task ffff8801d2405b80)
[56843.390711] Stack:
[56843.390714]  ffff8801d050dc48 ffffffff8104ee19 ffff8801d24c8e00 ffff8801dffa26c0
[56843.390726]  ffff8801d24c9400 0000000000000000 ffff8801d050dc78 ffffffff810545e8
[56843.390737]  ffff8801d050dc78 ffff8801dffa26c0 0000000000000001 ffff8801d2405f28
[56843.390748] Call Trace:
[56843.390758]  [<ffffffff8104ee19>] ? pick_next_entity+0xb9/0xe0
[56843.390765]  [<ffffffff810545e8>] pick_next_task_fair+0x38/0x70
[56843.390774]  [<ffffffff816530dc>] __schedule+0x14c/0x6f0
[56843.390781]  [<ffffffff816557ee>] ? _raw_spin_unlock_irqrestore+0x1e/0x30
[56843.390789]  [<ffffffff8165374f>] schedule+0x3f/0x60
[56843.390797]  [<ffffffff8117e209>] pipe_wait+0x59/0x80
[56843.390804]  [<ffffffff81089470>] ? add_wait_queue+0x60/0x60
[56843.390810]  [<ffffffff8117e96a>] pipe_read+0x1da/0x330
[56843.390817]  [<ffffffff81174612>] do_sync_read+0xd2/0x110
[56843.390824]  [<ffffffff8100a25d>] ? xen_force_evtchn_callback+0xd/0x10
[56843.390831]  [<ffffffff8100aa32>] ? check_events+0x12/0x20
[56843.390838]  [<ffffffff81298dc3>] ? security_file_permission+0x93/0xb0
[56843.390845]  [<ffffffff81174a91>] ? rw_verify_area+0x61/0xf0
[56843.390851]  [<ffffffff81174f70>] vfs_read+0xb0/0x180
[56843.390857]  [<ffffffff8117508a>] sys_read+0x4a/0x90
[56843.390863]  [<ffffffff8165dbc2>] system_call_fastpath+0x16/0x1b
[56843.390869] Code: 89 06 48 8b 47 08 48 89 46 08 48 8b 47 10 48 89 46 10 c3 0f 1f 80 00 00 00 00 48 89 32 eb b2 0f 1f 00 48 89 70 10 eb a9 66 90 55 <48> 8b 17 48 89 e5 48 89 d0 48 83 e0 fc 48 39 c7 74 34 48 8b 47 
[56843.390960] RIP  [<ffffffff8130d901>] rb_next+0x1/0x50
[56843.390967]  RSP <ffff8801d050dc18>
[56843.390970] CR2: 0000000000000010
[56843.390990] ---[ end trace ddb8957a1d924ccc ]---