Not quite sure if it's the same bug, but maybe this adds some more data points to the set. 

AMI ID is ami-405c6934, which is the eu-west-1 EBS-backed variant of the image in question.

Just a plain instance boot, connecting four EBS volumes, bundling them together as /dev/md0, putting XFS on top and running a benchmark as described in http://www.mysqlperformanceblog.com/2009/08/06/ec2ebs-single-and-raid-volumes-io-bencmark/.

When doing the same (on the same volumes) from a 32bit AMI on a .small instance the problem does not occur (at least not over a few days), whereas the 64bit AMI crashed within hours.

Dec  5 22:00:55 ip-10-234-243-114 kernel: [    6.642845] JBD: barrier-based sync failed on sda1-8 - disabling barriers
Dec  5 22:01:02 ip-10-234-243-114 kernel: [   13.890171] eth0: no IPv6 routers present
Dec  5 22:04:14 ip-10-234-243-114 kernel: [  205.786453] SGI XFS with ACLs, security attributes, realtime, large block/inode numbers, no debug enabled
Dec  5 22:04:14 ip-10-234-243-114 kernel: [  205.789239] SGI XFS Quota Management subsystem
Dec  5 22:04:14 ip-10-234-243-114 kernel: [  205.790489] Filesystem "md0": Disabling barriers, trial barrier write failed
Dec  5 22:04:14 ip-10-234-243-114 kernel: [  205.807777] XFS mounting filesystem md0
Dec  5 22:04:15 ip-10-234-243-114 kernel: [  206.368403] Ending clean XFS mount for filesystem: md0
Dec  5 22:07:36 ip-10-234-243-114 kernel: [  407.339573] Filesystem "md0": Disabling barriers, trial barrier write failed
Dec  5 22:07:36 ip-10-234-243-114 kernel: [  407.340479] XFS mounting filesystem md0
Dec  5 22:07:36 ip-10-234-243-114 kernel: [  407.593179] Ending clean XFS mount for filesystem: md0
Dec  5 22:17:01 ip-10-234-243-114 CRON[1222]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Dec  5 22:31:54 ip-10-234-243-114 kernel: [ 1865.812490] XFS mounting filesystem md0
Dec  5 22:31:54 ip-10-234-243-114 kernel: [ 1866.061941] Ending clean XFS mount for filesystem: md0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190047] INFO: task flush-9:0:1272 blocked for more than 120 seconds.
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190061] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190068] flush-9:0     D ffff880003e7d980     0  1272      2 0x00000000
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190072]  ffff88014d79b640 0000000000000246 ffff880100000000 0000000000015980
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190077]  ffff88014d79bfd8 0000000000015980 ffff88014d79bfd8 ffff8801d58316e0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190081]  0000000000015980 0000000000015980 ffff88014d79bfd8 0000000000015980
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190084] Call Trace:
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190095]  [<ffffffff815a20f3>] io_schedule+0x73/0xc0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190099]  [<ffffffff812a2f1c>] get_request_wait+0xcc/0x1a0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190104]  [<ffffffff8107f080>] ? autoremove_wake_function+0x0/0x40
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190107]  [<ffffffff812a3083>] __make_request+0x93/0x4b0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190111]  [<ffffffff81006adf>] ? __raw_callee_save_xen_restore_fl+0x11/0x1e
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190113]  [<ffffffff812a1c63>] generic_make_request+0x1b3/0x540
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190116]  [<ffffffff81006adf>] ? __raw_callee_save_xen_restore_fl+0x11/0x1e
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190121]  [<ffffffff81181862>] ? bvec_alloc_bs+0x62/0x110
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190125]  [<ffffffff81142b07>] ? kmem_cache_alloc+0x77/0x120
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190127]  [<ffffffff812a2072>] submit_bio+0x82/0x110
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190131]  [<ffffffff811760a2>] ? __mark_inode_dirty+0x42/0x1d0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190173]  [<ffffffffa00d2d37>] xfs_submit_ioend_bio+0x57/0x90 [xfs]
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190189]  [<ffffffffa00d2e22>] xfs_submit_ioend+0xb2/0x110 [xfs]
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190205]  [<ffffffffa00d3f98>] xfs_page_state_convert+0x348/0x6d0 [xfs]
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190222]  [<ffffffffa00d44d5>] xfs_vm_writepage+0x95/0x180 [xfs]
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190225]  [<ffffffff81006adf>] ? __raw_callee_save_xen_restore_fl+0x11/0x1e
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190230]  [<ffffffff81109417>] __writepage+0x17/0x40
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190233]  [<ffffffff8110a537>] write_cache_pages+0x1c7/0x3d0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190235]  [<ffffffff81109400>] ? __writepage+0x0/0x40
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190239]  [<ffffffff8110a764>] generic_writepages+0x24/0x30
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190254]  [<ffffffffa00d335d>] xfs_vm_writepages+0x5d/0x80 [xfs]
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190257]  [<ffffffff8110a791>] do_writepages+0x21/0x40
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190260]  [<ffffffff81175356>] writeback_single_inode+0xe6/0x3f0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190264]  [<ffffffff81175ab5>] writeback_sb_inodes+0x195/0x280
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190266]  [<ffffffff811762d0>] writeback_inodes_wb+0xa0/0x1b0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190269]  [<ffffffff8117662b>] wb_writeback+0x24b/0x2b0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190274]  [<ffffffff810709b2>] ? del_timer_sync+0x22/0x30
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190277]  [<ffffffff81176739>] wb_do_writeback+0xa9/0x190
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190279]  [<ffffffff8106ffd0>] ? process_timeout+0x0/0x10
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190282]  [<ffffffff81176873>] bdi_writeback_task+0x53/0x160
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190285]  [<ffffffff8107ef47>] ? bit_waitqueue+0x17/0xd0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190289]  [<ffffffff81119cb6>] bdi_start_fn+0x86/0x100
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190292]  [<ffffffff81119c30>] ? bdi_start_fn+0x0/0x100
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190294]  [<ffffffff8107eb26>] kthread+0x96/0xa0
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190298]  [<ffffffff8100aee4>] kernel_thread_helper+0x4/0x10
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190301]  [<ffffffff815a45dd>] ? retint_restore_args+0x5/0x6
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190304]  [<ffffffff8100aee0>] ? kernel_thread_helper+0x0/0x10
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190307] INFO: task xfsbufd/md0:1323 blocked for more than 120 seconds.
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190313] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190319] xfsbufd/md0   D ffff880003e7d980     0  1323      2 0x00000000
Dec  5 23:04:48 ip-10-234-243-114 kernel: [ 3840.190323]  ffff8801d761fb50 0000000000000246 ffffffff00000000 0000000000015980
...skipping...
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200074]  ffff8801d483bfd8 0000000000015980 ffff8801d483bfd8 ffff8801d5b10000
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200079]  0000000000015980 0000000000015980 ffff8801d483bfd8 0000000000015980
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200084] Call Trace:
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200096]  [<ffffffff815a404e>] ? _raw_spin_unlock_irqrestore+0x1e/0x30
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200134]  [<ffffffffa00c7147>] xlog_state_get_iclog_space+0xe7/0x2d0 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200140]  [<ffffffff81056c10>] ? default_wake_function+0x0/0x20
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200167]  [<ffffffffa00c7f74>] xlog_write+0x174/0x510 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200172]  [<ffffffff812a1c63>] ? generic_make_request+0x1b3/0x540
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200176]  [<ffffffff81006adf>] ? __raw_callee_save_xen_restore_fl+0x11/0x1e
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200191]  [<ffffffffa00c8387>] xfs_log_write+0x77/0xa0 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200209]  [<ffffffffa00d4af9>] xfs_trans_commit_iclog+0x169/0x300 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200225]  [<ffffffffa00c89c4>] ? xlog_grant_log_space+0x3f4/0x5d0 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200241]  [<ffffffffa00c8ca6>] ? xfs_log_reserve+0x106/0x170 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200256]  [<ffffffffa00d546d>] _xfs_trans_commit+0x8d/0x2c0 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200273]  [<ffffffffa00eb87e>] xfs_commit_dummy_trans+0x9e/0xf0 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200289]  [<ffffffffa00ebf44>] xfs_sync_worker+0x74/0x80 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200305]  [<ffffffffa00eb733>] xfssyncd+0x183/0x230 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200320]  [<ffffffffa00eb5b0>] ? xfssyncd+0x0/0x230 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200324]  [<ffffffff8107eb26>] kthread+0x96/0xa0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200327]  [<ffffffff8100aee4>] kernel_thread_helper+0x4/0x10
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200331]  [<ffffffff815a45dd>] ? retint_restore_args+0x5/0x6
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200334]  [<ffffffff8100aee0>] ? kernel_thread_helper+0x0/0x10
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200351] INFO: task flush-9:0:1078 blocked for more than 120 seconds.
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200357] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200364] flush-9:0     D ffff880003e5f980     0  1078      2 0x00000000
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200367]  ffff8801737ad640 0000000000000246 0000000000000000 0000000000015980
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200371]  ffff8801737adfd8 0000000000015980 ffff8801737adfd8 ffff8801d75f96e0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200375]  0000000000015980 0000000000015980 ffff8801737adfd8 0000000000015980
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200378] Call Trace:
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200381]  [<ffffffff815a20f3>] io_schedule+0x73/0xc0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200384]  [<ffffffff812a2f1c>] get_request_wait+0xcc/0x1a0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200387]  [<ffffffff8107f080>] ? autoremove_wake_function+0x0/0x40
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200389]  [<ffffffff812a3083>] __make_request+0x93/0x4b0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200392]  [<ffffffff81006adf>] ? __raw_callee_save_xen_restore_fl+0x11/0x1e
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200395]  [<ffffffff812a1c63>] generic_make_request+0x1b3/0x540
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200398]  [<ffffffff81006adf>] ? __raw_callee_save_xen_restore_fl+0x11/0x1e
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200402]  [<ffffffff81181862>] ? bvec_alloc_bs+0x62/0x110
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200406]  [<ffffffff81142b07>] ? kmem_cache_alloc+0x77/0x120
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200408]  [<ffffffff812a2072>] submit_bio+0x82/0x110
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200412]  [<ffffffff811760a2>] ? __mark_inode_dirty+0x42/0x1d0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200427]  [<ffffffffa00ddd37>] xfs_submit_ioend_bio+0x57/0x90 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200441]  [<ffffffffa00dde22>] xfs_submit_ioend+0xb2/0x110 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200456]  [<ffffffffa00def98>] xfs_page_state_convert+0x348/0x6d0 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200471]  [<ffffffffa00df4d5>] xfs_vm_writepage+0x95/0x180 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200474]  [<ffffffff81006adf>] ? __raw_callee_save_xen_restore_fl+0x11/0x1e
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200478]  [<ffffffff81109417>] __writepage+0x17/0x40
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200481]  [<ffffffff8110a537>] write_cache_pages+0x1c7/0x3d0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200483]  [<ffffffff81109400>] ? __writepage+0x0/0x40
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200487]  [<ffffffff8110a764>] generic_writepages+0x24/0x30
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200501]  [<ffffffffa00de35d>] xfs_vm_writepages+0x5d/0x80 [xfs]
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200504]  [<ffffffff8110a791>] do_writepages+0x21/0x40
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200507]  [<ffffffff81175356>] writeback_single_inode+0xe6/0x3f0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200510]  [<ffffffff81175ab5>] writeback_sb_inodes+0x195/0x280
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200513]  [<ffffffff811762d0>] writeback_inodes_wb+0xa0/0x1b0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200516]  [<ffffffff8117662b>] wb_writeback+0x24b/0x2b0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200520]  [<ffffffff810709b2>] ? del_timer_sync+0x22/0x30
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200523]  [<ffffffff81176739>] wb_do_writeback+0xa9/0x190
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200526]  [<ffffffff8106ffd0>] ? process_timeout+0x0/0x10
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200529]  [<ffffffff81176873>] bdi_writeback_task+0x53/0x160
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200531]  [<ffffffff8107ef47>] ? bit_waitqueue+0x17/0xd0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200535]  [<ffffffff81119cb6>] bdi_start_fn+0x86/0x100
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200538]  [<ffffffff81119c30>] ? bdi_start_fn+0x0/0x100
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200540]  [<ffffffff8107eb26>] kthread+0x96/0xa0
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200542]  [<ffffffff8100aee4>] kernel_thread_helper+0x4/0x10
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200546]  [<ffffffff815a45dd>] ? retint_restore_args+0x5/0x6
Dec  6 00:36:00 ip-10-235-98-89 kernel: [ 3960.200548]  [<ffffffff8100aee0>] ? kernel_thread_helper+0x0/0x10