I've been seeing the same problem from doing an iozone test on an mdraid 5 array.  This keeps appearing in my dmesg:

[553927.303743] BUG: soft lockup - CPU#3 stuck for 61s! [iozone:24558]
[553927.303755] Modules linked in: wmi video output sbs sbshc pci_slot battery ac bonding iptable_filter ip_tables x_tables parport_pc lp parport loop evdev pcspkr snd_intel8x0 snd_ac97_codec shpchp pci_hotplug k8temp isp1760 ac97_bus snd_pcm snd_timer snd soundcore snd_page_alloc cfi_cmdset_0002 cfi_util container jedec_probe cfi_probe gen_probe button ck804xrom mtd chipreg i2c_nforce2 map_funcs i2c_core ipv6 xfs sr_mod cdrom pata_amd sata_nv sd_mod crc_t10dif sg usb_storage libusual pata_acpi sata_sil24 ata_generic libata scsi_mod ehci_hcd forcedeth ohci_hcd dock usbcore raid10 raid456 async_xor async_memcpy async_tx xor raid1 raid0 multipath linear md_mod thermal processor fan fuse vesafb fbcon tileblit font bitblit softcursor
[553927.303755] CPU 3:
[553927.303755] Modules linked in: wmi video output sbs sbshc pci_slot battery ac bonding iptable_filter ip_tables x_tables parport_pc lp parport loop evdev pcspkr snd_intel8x0 snd_ac97_codec shpchp pci_hotplug k8temp isp1760 ac97_bus snd_pcm snd_timer snd soundcore snd_page_alloc cfi_cmdset_0002 cfi_util container jedec_probe cfi_probe gen_probe button ck804xrom mtd chipreg i2c_nforce2 map_funcs i2c_core ipv6 xfs sr_mod cdrom pata_amd sata_nv sd_mod crc_t10dif sg usb_storage libusual pata_acpi sata_sil24 ata_generic libata scsi_mod ehci_hcd forcedeth ohci_hcd dock usbcore raid10 raid456 async_xor async_memcpy async_tx xor raid1 raid0 multipath linear md_mod thermal processor fan fuse vesafb fbcon tileblit font bitblit softcursor
[553927.303755] Pid: 24558, comm: iozone Not tainted 2.6.27-11-server #1
[553927.303755] RIP: 0010:[<ffffffff802abea6>]  [<ffffffff802abea6>] find_get_pages+0x66/0x110
[553927.303755] RSP: 0018:ffff88015ccfd368  EFLAGS: 00000246
[553927.303755] RAX: ffff880048befce0 RBX: ffff88015ccfd3a8 RCX: 0000000000000003
[553927.303755] RDX: 0000000000000004 RSI: 0000000000000000 RDI: ffffe20002055800
[553927.303755] RBP: ffff88015ccfd318 R08: ffffe20000bdafc8 R09: 0000000000000008
[553927.303755] R10: 000000000000003e R11: 000000000015dcbf R12: ffffffff802b6ba9
[553927.303755] R13: ffff8801e1450a10 R14: ffffe20000bdae40 R15: 0000000000000282
[553927.303755] FS:  00007f4b4d13c6e0(0000) GS:ffff88025fa2c700(0000) knlGS:0000000000000000
[553927.303755] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[553927.303755] CR2: 00007fa32cff2e40 CR3: 000000015f036000 CR4: 00000000000006e0
[553927.303755] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[553927.303755] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[553927.303755] 
[553927.303755] Call Trace:
[553927.303755]  [<ffffffff802abe83>] ? find_get_pages+0x43/0x110
[553927.303755]  [<ffffffff802b6a04>] ? pagevec_lookup+0x24/0x30
[553927.303755]  [<ffffffffa026801d>] ? xfs_cluster_write+0xad/0x180 [xfs]
[553927.303755]  [<ffffffffa0268588>] ? xfs_page_state_convert+0x498/0x760 [xfs]
[553927.303755]  [<ffffffffa02689b1>] ? xfs_vm_writepage+0x71/0x120 [xfs]
[553927.303755]  [<ffffffff802b92f4>] ? pageout+0x124/0x270
[553927.303755]  [<ffffffff802ab00a>] ? page_waitqueue+0xa/0x90
[553927.303755]  [<ffffffff802b98ed>] ? shrink_page_list+0x34d/0x530
[553927.303755]  [<ffffffff802b9c72>] ? shrink_inactive_list+0x1a2/0x4b0
[553927.303755]  [<ffffffff802b4874>] ? get_dirty_limits+0x14/0x2b0
[553927.303755]  [<ffffffff802b9ffb>] ? shrink_zone+0x7b/0x160
[553927.303755]  [<ffffffff802ba16d>] ? shrink_zones+0x8d/0x150
[553927.303755]  [<ffffffff802ba2b6>] ? do_try_to_free_pages+0x86/0x2e0
[553927.303755]  [<ffffffff802ba607>] ? try_to_free_pages+0x67/0x70
[553927.303755]  [<ffffffff802b9120>] ? isolate_pages_global+0x0/0x50
[553927.303755]  [<ffffffff802b2931>] ? __alloc_pages_internal+0x241/0x510
[553927.303755]  [<ffffffff802d59ad>] ? alloc_pages_current+0xad/0x110
[553927.303755]  [<ffffffff802ac417>] ? __page_cache_alloc+0x67/0x80
[553927.303755]  [<ffffffff802ad053>] ? __grab_cache_page+0x63/0xb0
[553927.303755]  [<ffffffff80316e49>] ? block_write_begin+0x89/0xf0
[553927.303755]  [<ffffffffa02674da>] ? xfs_vm_write_begin+0x2a/0x30 [xfs]
[553927.303755]  [<ffffffffa0267050>] ? xfs_get_blocks+0x0/0x20 [xfs]
[553927.303755]  [<ffffffff802ab74c>] ? generic_perform_write+0xbc/0x1c0
[553927.303755]  [<ffffffff802ad4b2>] ? generic_file_buffered_write+0x92/0x170
[553927.303755]  [<ffffffffa02702e3>] ? xfs_write+0x6b3/0x9b0 [xfs]
[553927.303755]  [<ffffffffa026fc31>] ? xfs_write+0x1/0x9b0 [xfs]
[553927.303755]  [<ffffffffa026bc98>] ? xfs_file_aio_write+0x58/0x60 [xfs]
[553927.303755]  [<ffffffff802e98a9>] ? do_sync_write+0xf9/0x140
[553927.303755]  [<ffffffff803a7cd1>] ? __rb_erase_color+0x101/0x1d0
[553927.303755]  [<ffffffff80266fd0>] ? autoremove_wake_function+0x0/0x40
[553927.303755]  [<ffffffff80387011>] ? aa_file_permission+0x21/0xf0
[553927.303755]  [<ffffffff80387138>] ? apparmor_file_permission+0x28/0x30
[553927.303755]  [<ffffffff80361be6>] ? security_file_permission+0x16/0x20
[553927.303755]  [<ffffffff802e9f6b>] ? vfs_write+0xcb/0x130
[553927.303755]  [<ffffffff802ea0c5>] ? sys_write+0x55/0x90
[553927.303755]  [<ffffffff8021285a>] ? system_call_fastpath+0x16/0x1b
[553927.303755]