[Xen-devel] blktap: Indirection in vm_area_struct->vm_private_data

[Grzegorz Milos <gm281@xxxxxxxxx>]

Hi all,

The recent patch in linux-2.6.18.hg (878: eba6fe6d8d53) changed the
way that the foreign map is stored in vm_area_struct. Currently blktap
(not 2) implementation is internally inconsistent, which triggers
kernel bug when tap:aio disk is used (dump attached at the end of the
email).

The problem is that the above patch added an extra level of
indirection to how the raw foreign map is stored. mm/memory.c and
blktap2/ring.c expect the map to be accessible through
vm_area_struct->vm_private_data->map, whereas blktap still assigns
vm_area_struct->vm_private_data as if was pointing to the map
directly. I'm attaching a patch that fixes one of these assignments,
but there are two more (in blktap_vma_open & blktap_vma_close) which
need to be fixed (I'm not hitting these in my testing setup). I'm not
attempting to fix the two remaining assignments, because the
foreign_map structure in tap_blkif_t can not be used there. You'll
know if its better to create foreign_map structure dynamically, every
time the assignment is made, or statically, once for each affected
vm_area_struct.

Thanks
Gregor

Jun  8 17:59:30 knockout kernel: blktap: ring-ref 1536, event-channel
5, protocol 2 (x86_32-abi)
Jun  8 17:59:33 knockout kernel: Unable to handle kernel NULL pointer
dereference at 0000000000000008 RIP:
Jun  8 17:59:33 knockout kernel:  [<ffffffff8026c2b5>]
get_user_pages+0x359/0x50b
Jun  8 17:59:33 knockout kernel: PGD 1fcd0067 PUD 1fcd1067 PMD 0
Jun  8 17:59:33 knockout kernel: Oops: 0000 [1] SMP
Jun  8 17:59:33 knockout kernel: CPU 1
Jun  8 17:59:33 knockout kernel: Modules linked in: ipv6
Jun  8 17:59:33 knockout kernel: Pid: 3528, comm: tapdisk Not tainted
2.6.18.8-xen #4
Jun  8 17:59:33 knockout kernel: RIP: e030:[<ffffffff8026c2b5>]
[<ffffffff8026c2b5>] get_user_pages+0x359/0x50b
Jun  8 17:59:33 knockout kernel: RSP: e02b:ffff8800202e7bd8  EFLAGS: 00010202
Jun  8 17:59:33 knockout kernel: RAX: 0000000000000000 RBX:
0000000000000001 RCX: 00000000040a44fb
Jun  8 17:59:33 knockout kernel: RDX: 0000000000000001 RSI:
00002b2b4cac4000 RDI: ffff88006f45c780
Jun  8 17:59:33 knockout kernel: RBP: ffff880031883870 R08:
0000000000000001 R09: 0000000000000000
Jun  8 17:59:33 knockout kernel: R10: 0000000000010a17 R11:
0000000000000001 R12: 0000000000000000
Jun  8 17:59:33 knockout kernel: R13: 00002b2b4cac4000 R14:
0000000000000000 R15: 0000000000000009
Jun  8 17:59:33 knockout kernel: FS:  00002b2b4d9d9af0(0000)
GS:ffffffff805c9080(0000) knlGS:0000000000000000
Jun  8 17:59:33 knockout kernel: CS:  e033 DS: 0000 ES: 0000
Jun  8 17:59:33 knockout kernel: Process tapdisk (pid: 3528,
threadinfo ffff8800202e6000, task ffff88002506f820)
Jun  8 17:59:33 knockout kernel: Stack:  0000000000000000
0000000000000002 0000000100000001 ffff88006f45c780
Jun  8 17:59:33 knockout kernel:  ffff88002506f820 0000000000000001
ffff88006f66d400 0000000000000000
Jun  8 17:59:33 knockout kernel:  0000000000000200 0000000000000000
0000000000000009 ffffffff802a3812
Jun  8 17:59:33 knockout kernel: Call Trace:
Jun  8 17:59:33 knockout kernel:  [<ffffffff802a3812>] dio_get_page+0x8a/0x1a0
Jun  8 17:59:33 knockout kernel:  [<ffffffff802a445c>]
__blockdev_direct_IO+0x485/0xb49
Jun  8 17:59:33 knockout kernel:  [<ffffffff802c9251>] ext3_direct_IO+0xe3/0x16b
Jun  8 17:59:33 knockout kernel:  [<ffffffff802c9f54>] ext3_get_block+0x0/0xe4
Jun  8 17:59:33 knockout kernel:  [<ffffffff8025ebf1>]
generic_file_direct_IO+0x9f/0xe1
Jun  8 17:59:33 knockout kernel:  [<ffffffff8025f516>]
__generic_file_aio_read+0xc8/0x1b1
Jun  8 17:59:33 knockout kernel:  [<ffffffff8027ceae>]
cache_alloc_refill+0x9d/0x564
Jun  8 17:59:33 knockout kernel:  [<ffffffff8025f7a0>]
generic_file_aio_read+0x34/0x39
Jun  8 17:59:33 knockout kernel:  [<ffffffff8029d370>] aio_pread+0x34/0x97
Jun  8 17:59:33 knockout kernel:  [<ffffffff8029d33c>] aio_pread+0x0/0x97
Jun  8 17:59:33 knockout kernel:  [<ffffffff8029e872>] aio_run_iocb+0x108/0x1d1
Jun  8 17:59:33 knockout kernel:  [<ffffffff8029f3d5>] io_submit_one+0x274/0x2f5
Jun  8 17:59:33 knockout kernel:  [<ffffffff8029f4f7>] sys_io_submit+0xa1/0x10a
Jun  8 17:59:33 knockout kernel:  [<ffffffff8020a634>] system_call+0x68/0x6d
Jun  8 17:59:33 knockout kernel:  [<ffffffff8020a5cc>] system_call+0x0/0x6d
Jun  8 17:59:33 knockout kernel:
Jun  8 17:59:33 knockout kernel:
Jun  8 17:59:33 knockout kernel: Code: 48 8b 14 d0 48 85 d2 74 59 48
83 7c 24 60 00 74 1f 48 8b 4c
Jun  8 17:59:33 knockout kernel: RIP  [<ffffffff8026c2b5>]
get_user_pages+0x359/0x50b
Jun  8 17:59:33 knockout kernel:  RSP <ffff8800202e7bd8>
Jun  8 17:59:33 knockout kernel: CR2: 0000000000000008

blktap.patch
Description: Text Data

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