So this looks mostly problem free on my boxen, except this warning triggers:

Adding 3911820k swap on /dev/sda2.  Priority:-1 extents:1 across:3911820k 
capability: warning: `dbus-daemon' uses 32-bit capabilities (legacy support in use)
------------[ cut here ]------------
WARNING: CPU: 1 PID: 2445 at arch/x86/entry/common.c:311 syscall_return_slowpath+0x4c/0x270()
syscall 6 left IRQs disabled
Modules linked in:
CPU: 1 PID: 2445 Comm: distccd Not tainted 4.2.0-rc1-01597-gaecd781-dirty #18
 0000000000000000 00000000776afac2 ffff880035413e58 ffffffff81c8915f
 0000000000000000 ffff880035413eb0 ffff880035413e98 ffffffff810a8d82
 ffff880035413e78 ffff880035413f58 0000000020020002 ffff880035410000
Call Trace:
 [<ffffffff81c8915f>] dump_stack+0x4f/0x7b
 [<ffffffff810a8d82>] warn_slowpath_common+0xa2/0xc0
 [<ffffffff810a8df5>] warn_slowpath_fmt+0x55/0x70
 [<ffffffff81001ddc>] syscall_return_slowpath+0x4c/0x270
 [<ffffffff81c96471>] int_ret_from_sys_call+0x25/0x9f
---[ end trace 083efc734e089d37 ]---
device: 'vcs2': device_add
PM: Adding info for No Bus:vcs2
device: 'vcsa2': device_add

with ancient user-space, running the attached .config.

The system booted up fine otherwise. The warning corresponds to:

        if (WARN(irqs_disabled(), "syscall %ld left IRQs disabled",
                 regs->orig_ax))
                local_irq_enable();

and this was just the regular startup of the distccd daemon during bootup, nothing 
particularly fancy.

Note that 'distccd' is a 32-bit ELF binary - and this is a 64-bit kernel.

Syscall 6 would be:

arch/x86/entry/syscalls/syscall_32.tbl:6        i386    close                   sys_close

Thanks,

	Ingo