[Xen-devel] BUG: unable to handle kernel NULL pointer dereference (4.0.1 w/2.6.32.36)

[Quartexx <quartex73@xxxxxxxxx>]

Hi.
xen 4.0.1 with kernel 2.6.32.36.
I noticed in the last 2 days two kernel panics in the night (and two
reboots thanks to sysctl value kernel.panic)

This is the output I captured from netconsole:

[491154.766766] BUG: unable to handle kernel NULL pointer dereference
at 0000000000000320
[491154.767477] IP: [<ffffffff8128cbc3>] blktap_device_end_request+0x4a/0x71
[491154.767844] PGD 3db17067 PUD 3cebe067 PMD 0
[491154.768219] Oops: 0000 [#1] SMP
[491154.768572] last sysfs file: /sys/devices/vbd-4-51713/statistics/wr_sect
[491154.768942] CPU 3
[491154.769295] Modules linked in: netconsole [last unloaded: scsi_wait_scan]
[491154.769683] Pid: 4392, comm: tapdisk2 Not tainted 2.6.32.36 #4 S3420GP
[491154.770056] RIP: e030:[<ffffffff8128cbc3>]   [<ffffffff8128cbc3>]
blktap_device_end_request+0x4a/0x71
[491154.770767] RSP: e02b:ffff88003cd33ca8  EFLAGS: 00010046
[491154.771133] RAX: 0000000000000000 RBX: ffff88003df60d20 RCX:
0000000000000000
[491154.771824] RDX: 00000000000000a1 RSI: 0000000000000001 RDI:
0000000000000004
[491154.772524] RBP: ffff88003cd33cc8 R08: 0000000000000000 R09:
ffff88003cd33b08
[491154.773222] R10: 0000000000000001 R11: ffffffff00001000 R12:
ffff88003ccadb20
[491154.773915] R13: ffff88003d8e3c00 R14: 0000000000000000 R15:
0000000000000002
[491154.774622] FS:  00007f152f810740(0000) GS:ffff88002808f000(0000)
knlGS:0000000000000000
[491154.775325] CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
[491154.775683] CR2: 0000000000000320 CR3: 000000003b095000 CR4:
0000000000002660
[491154.776380] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[491154.777079] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
0000000000000400
[491154.777770] Process tapdisk2 (pid: 4392, threadinfo
ffff88003cd32000, task ffff88003d833c80)
[491154.778476] Stack:
[491154.778821]  ffff88003d8e3c00 0000000000000000 ffff88003ccadb20
0000000000e5386f
[491154.779220] <0> ffff88003cd33e58 ffffffff8128beab 000000003cd33ce8
ffffffff81aab128
[491154.779956] <0> 000000013d743ac0 ffff88003d7439a0 000000019681a000
ffff88003fffc800
[491154.780987] Call Trace:
[491154.781334]  [<ffffffff8128beab>] blktap_ring_ioctl+0x12d/0x23f
[491154.781676]  [<ffffffff811d503b>] ? avc_has_perm+0x57/0x69
[491154.782017]  [<ffffffff811d6322>] ? inode_has_perm+0x5f/0x61
[491154.782368]  [<ffffffff810e13b3>] ? generic_file_aio_write+0x8c/0xa9
[491154.782718]  [<ffffffff8111fd46>] vfs_ioctl+0x6a/0x82
[491154.783072]  [<ffffffff81120248>] do_vfs_ioctl+0x473/0x4b9
[491154.783426]  [<ffffffff811202df>] sys_ioctl+0x51/0x74
[491154.783781]  [<ffffffff8103ccc2>] system_call_fastpath+0x16/0x1b
[491154.784142] Code: e6 4c 89
[491154.795155]  [<ffffffff81120248>] do_vfs_ioctl+0x473/0x4b9


There are 4 pv guest running using tap2:aio backend.
Any hint or workaround to avoid this condition?  And why this happen?
Thanks in advance

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