Comment 32 for bug 1413540

Hrmn... When I repeated the setup I seem to have triggered some kind of lockup even while bringing up l2. Of course hard to say without details of Ryan's dump. However mine seems to have backtraces in the log which remind me an awful lot of an issue related to punching holes into ext4 based qcow images. Chris had been working on something like this before... He is on a sprint this week. Anyway, my strace in the log:

[ 1200.288031] INFO: task qemu-system-x86:4545 blocked for more than 120 seconds.
[ 1200.288712] Not tainted 3.13.0-46-generic #77-Ubuntu
[ 1200.289204] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1200.289892] qemu-system-x86 D ffff88007fc134c0 0 4545 1 0x00000000
[ 1200.289895] ffff88007a9c5d28 0000000000000082 ffff88007bbd3000 ffff88007a9c5fd8
[ 1200.289897] 00000000000134c0 00000000000134c0 ffff88007bbd3000 ffff88007fc13d58
[ 1200.289898] ffff88007ffcdee8 0000000000000002 ffffffff8114eef0 ffff88007a9c5da0
[ 1200.289900] Call Trace:
[ 1200.289906] [<ffffffff8114eef0>] ? wait_on_page_read+0x60/0x60
[ 1200.289909] [<ffffffff817259fd>] io_schedule+0x9d/0x140
[ 1200.289910] [<ffffffff8114eefe>] sleep_on_page+0xe/0x20
[ 1200.289912] [<ffffffff81725e82>] __wait_on_bit+0x62/0x90
[ 1200.289914] [<ffffffff8114ecbf>] wait_on_page_bit+0x7f/0x90
[ 1200.289917] [<ffffffff810ab140>] ? autoremove_wake_function+0x40/0x40
[ 1200.289919] [<ffffffff8115c4a1>] ? pagevec_lookup_tag+0x21/0x30
[ 1200.289921] [<ffffffff8114edc9>] filemap_fdatawait_range+0xf9/0x190
[ 1200.289923] [<ffffffff8115066f>] filemap_write_and_wait_range+0x3f/0x70
[ 1200.289927] [<ffffffff8123bc4a>] ext4_sync_file+0xba/0x320
[ 1200.289930] [<ffffffff811ede21>] do_fsync+0x51/0x80
[ 1200.289931] [<ffffffff811ee0d3>] SyS_fdatasync+0x13/0x20
[ 1200.289933] [<ffffffff81731d7d>] system_call_fastpath+0x1a/0x1f