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[Xen-devel] Shutdown crash via blkback

To: Daniel Stodden <daniel.stodden@xxxxxxxxxx>
Subject: [Xen-devel] Shutdown crash via blkback
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 12 Apr 2011 15:13:18 -0700
Cc: Jens Axboe <axboe@xxxxxxxxx>, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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I got this when rebooting dom0 with a running domain.  It's from blkback
rather than blktap, so I don't think its precisely the problem I saw before.

The oops is:

void md_write_start(mddev_t *mddev, struct bio *bi)
        int did_change = 0;
        if (bio_data_dir(bi) != WRITE)

        BUG_ON(mddev->ro == 1);

but I'm not sure if this means that blkback should suppress writes when
the underlying device goes RO, or if MD shouldn't be getting into this
state of attempting to write to an RO device (I'd expect it to return
error codes).


Please stand by while rebooting the system...
md: stopping all md devices.
xenbus_dev_shutdown: backend/console/7/0: Initialising != Connected, skipping
xenbus_dev_shutdown: backend/vkbd/7/0: Initialising != Connected, skipping
xenbus_dev_shutdown: backend/vfb/7/0: Initialising != Connected, skipping
------------[ cut here ]------------
kernel BUG at /home/jeremy/git/upstream/drivers/md/md.c:6613!
invalid opcode: 0000 [#1] SMP 
last sysfs file: /sys/devices/virtual/block/dm-2/dm/name
CPU 0 
Modules linked in: xt_physdev nfsd lockd nfs_acl auth_rpcgss sunrpc bridge stp 
llc usblp microcode e1000e xts gf128mul raid10 ahci libahci [last unloaded: 

Pid: 31550, comm: blkback.7.xvda Not tainted 2.6.39-rc2+ #368 Supermicro 
RIP: e030:[<ffffffff813789f2>]  [<ffffffff813789f2>] md_write_start+0x27/0x163
RSP: e02b:ffff8800624f3880  EFLAGS: 00010246
RAX: 0000000000000001 RBX: ffff88000721e800 RCX: 000000003ea3b1c8
RDX: 00000000000007ff RSI: ffff88005a64db00 RDI: ffff88000721e800
RBP: ffff8800624f38d0 R08: 0000000000001000 R09: ffff8800063128c0
R10: 0000000000000008 R11: 0000000000000008 R12: ffff88005a64db00
R13: ffff88005a64db00 R14: ffff88000721e800 R15: 0000000000000001
FS:  00007f2bb9322720(0000) GS:ffff88007fae7000(0000) knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007fff5951c8c0 CR3: 00000000663cc000 CR4: 0000000000002660
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process blkback.7.xvda (pid: 31550, threadinfo ffff8800624f2000, task 
 0000000000001000 0000000000000001 ffff880007216cfc 0000000000001000
 0000000000000001 0000000000000000 ffff8800624f38d0 ffff880067701d80
 ffff88005a64db00 ffff88005a64db00 ffff8800624f3940 ffffffffa001e4d9
Call Trace:
 [<ffffffffa001e4d9>] make_request+0x18c/0x4e4 [raid10]
 [<ffffffff813788d4>] md_make_request+0xcf/0x1c6
 [<ffffffff812087fb>] generic_make_request+0x32a/0x39e
 [<ffffffff8138460a>] ? dm_get_live_table+0x44/0x4f
 [<ffffffff813846cf>] ? dm_merge_bvec+0xba/0xdf
 [<ffffffff81208946>] submit_bio+0xd7/0xe2
 [<ffffffff8129429d>] dispatch_rw_block_io+0x512/0x5dd
 [<ffffffff81006c3d>] ? xen_force_evtchn_callback+0xd/0xf
 [<ffffffff810071f2>] ? check_events+0x12/0x20
 [<ffffffff81004226>] ? xen_mc_flush+0x172/0x1a8
 [<ffffffff81026295>] ? paravirt_end_context_switch+0x17/0x31
 [<ffffffff81003530>] ? xen_end_context_switch+0x1f/0x21
 [<ffffffff8100966d>] ? __switch_to+0x14c/0x281
 [<ffffffff81035420>] ? finish_task_switch+0x59/0x9e
 [<ffffffff814f9eb9>] ? schedule+0x804/0x8b5
 [<ffffffff81006c3d>] ? xen_force_evtchn_callback+0xd/0xf
 [<ffffffff810071f2>] ? check_events+0x12/0x20
 [<ffffffff812945bc>] do_block_io_op+0x254/0x2b8
 [<ffffffff81006c3d>] ? xen_force_evtchn_callback+0xd/0xf
 [<ffffffff812947d5>] blkif_schedule+0x1b5/0x391
 [<ffffffff810071f2>] ? check_events+0x12/0x20
 [<ffffffff8105aa03>] ? wake_up_bit+0x2a/0x2a
 [<ffffffff81294620>] ? do_block_io_op+0x2b8/0x2b8
 [<ffffffff8105a51d>] kthread+0x82/0x8a
 [<ffffffff81503b44>] kernel_thread_helper+0x4/0x10
 [<ffffffff814fc401>] ? retint_restore_args+0x13/0x13
 [<ffffffff81503b40>] ? gs_change+0x13/0x13
Code: 41 5f c9 c3 55 48 89 e5 41 55 41 54 53 48 83 ec 38 0f 1f 44 00 00 48 89 
fb f6 46 20 01 0f 84 39 01 00 00 8b 47 38 83 f8 01 75 02 <0f> 0b 45 31 e4 83 f8 
02 75 2a c7 47 38 00 00 00 00 f0 80 8f a8 
RIP  [<ffffffff813789f2>] md_write_start+0x27/0x163
 RSP <ffff8800624f3880>
---[ end trace a0aa4b26f40c2143 ]---

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