Created attachment 415298 [details]
a backport patch for aoe driver

Description of problem:
  xen blkbk driver generates call traces when used with aoe

Version-Release number of selected component (if applicable):
  kernel-xen-2.6.18-194.el5

How reproducible:
  Always reproducible when aoe devices are attached to Xen domU guests.

Steps to Reproduce:
  1. Setup an AoE server, and an AoE client as Xen dom0.
  2. Create a Xen guest.
  3. Attach aoe devices to the Xen domU guest above.
  4. You would see bunch of Call Traces like the bottom.
  
Actual results:
  Got bunch of call trace messages.

Expected results:
  Do not see call trace messages.

Additional info:
  This is because aoe driver does not follow block subsystem initialization rule, and xenblk back is a victim of the bug. Essentialy the problem was fixed in linux-2.6.32. 
  http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=7135a71b19be1faf48b7148d77844d03bc0717d6

I wrote a backport patch as attached(fix_aoe_calltraces_backport.patch).

Note that under some rare conditions, the above fix is not enough, and we need one more aoe patch which I posted to upstream. I'm posting the fix in another bug report. 

The following is an example of call traces which I got:
May  6 18:54:59 cb-blsv3d1 kernel: BUG: warning at lib/kref.c:32/kref_get() (Not tainted)
May  6 18:54:59 cb-blsv3d1 kernel:
May  6 18:54:59 cb-blsv3d1 kernel: Call Trace:
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80237b0b>] kref_get+0x38/0x3d
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80259c09>] kobject_get+0x12/0x17
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff8024acad>] blk_get_queue+0x1f/0x26
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff8839390a>] :blkbk:dispatch_rw_block_io+0x4e4/0x5ab
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80263f77>] __kprobes_text_start+0x317/0x438
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80286570>] dequeue_task+0x18/0x37
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff802865b7>] deactivate_task+0x28/0x60
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff8026df02>] monotonic_clock+0x35/0x7b
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80261e83>] thread_return+0x6c/0x113
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff8020622a>] hypercall_page+0x22a/0x1000
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff8033b517>] kobject_cleanup+0x39/0x7e
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff88393d4b>] :blkbk:blkif_schedule+0x37a/0x463
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff883939d1>] :blkbk:blkif_schedule+0x0/0x463
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80299db3>] keventd_create_kthread+0x0/0xc4
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80233476>] kthread+0xfe/0x132
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff8025fb2c>] child_rip+0xa/0x12
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80299db3>] keventd_create_kthread+0x0/0xc4
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff80233378>] kthread+0x0/0x132
May  6 18:54:59 cb-blsv3d1 kernel:  [<ffffffff8025fb22>] child_rip+0x0/0x12