On Wed, 2011-09-21 at 12:17 +0200, Mike Galbraith wrote:

[  144.212272] ------------[ cut here ]------------
[  144.212280] WARNING: at kernel/sched.c:6152 migrate_disable+0x1b6/0x200()
[  144.212282] Hardware name: MS-7502
[  144.212283] Modules linked in: snd_pcm_oss snd_mixer_oss snd_seq snd_seq_device edd nfsd lockd parport_pc parport nfs_acl auth_rpcgss sunrpc bridge ipv6 stp cpufreq_conservative microcode cpufreq_ondemand cpufreq_userspace cpufreq_powersave acpi_cpufreq mperf nls_iso8859_1 nls_cp437 vfat fat fuse ext3 jbd dm_mod usbmouse usb_storage usbhid snd_hda_codec_realtek usb_libusual uas sr_mod cdrom hid snd_hda_intel e1000e snd_hda_codec kvm_intel snd_hwdep sg snd_pcm kvm i2c_i801 snd_timer snd firewire_ohci firewire_core soundcore snd_page_alloc crc_itu_t button ext4 mbcache jbd2 crc16 uhci_hcd sd_mod ehci_hcd usbcore rtc_cmos ahci libahci libata scsi_mod fan processor thermal
[  144.212317] Pid: 6215, comm: strace Not tainted 3.0.4-rt14 #2052
[  144.212319] Call Trace:
[  144.212323]  [<ffffffff8104662f>] warn_slowpath_common+0x7f/0xc0
[  144.212326]  [<ffffffff8104668a>] warn_slowpath_null+0x1a/0x20
[  144.212328]  [<ffffffff8103f606>] migrate_disable+0x1b6/0x200
[  144.212331]  [<ffffffff8105a2a8>] ptrace_stop+0x128/0x240
[  144.212334]  [<ffffffff81057b9b>] ? recalc_sigpending+0x1b/0x50
[  144.212337]  [<ffffffff8105b6f1>] get_signal_to_deliver+0x211/0x530
[  144.212340]  [<ffffffff81001835>] do_signal+0x75/0x7a0
[  144.212342]  [<ffffffff8105ae68>] ? kill_pid_info+0x58/0x80
[  144.212344]  [<ffffffff8105c34c>] ? sys_kill+0xac/0x1e0
[  144.212347]  [<ffffffff81001fe5>] do_notify_resume+0x65/0x80
[  144.212350]  [<ffffffff8135978b>] int_signal+0x12/0x17
[  144.212352] ---[ end trace 0000000000000002 ]---

Right, that's because of 
53da1d9456fe7f87a920a78fdbdcf1225d197cb7, I think we simply want a full
revert of that for -rt.