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SubjectRandom crashes with v4l2_device_register_subdev
Date
Hi,

Recently I received a report about crashes with mxb v4l driver
(https://bugs.launchpad.net/ubuntu/+source/linux/+bug/745213), there are
two slightly different reported crashes which I paste here:

1) BootDmesg.txt crash:

[ 21.210232] general protection fault: 0000 [#1] SMP
[ 21.210292] last sysfs file: /sys/bus/i2c/drivers/tda9840/uevent
[ 21.210357] CPU 0
[ 21.210379] Modules linked in: tda9840 tea6415c tea6420 snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_intel snd_hda_codec saa7115 mxb(+) snd_seq_midi snd_hwdep snd_rawmidi snd_pcm snd_seq_midi_event snd_seq snd_timer snd_seq_device saa7146_vv saa7146 snd videobuf_dma_sg videobuf_core v4l2_common videodev edac_core soundcore shpchp snd_page_alloc sp5100_tco edac_mce_amd xhci_hcd v4l2_compat_ioctl32 k10temp i2c_piix4 asus_atk0110 lp parport radeon usbhid ttm hid drm_kms_helper drm ahci sym53c8xx firewire_ohci e1000 scsi_transport_spi r8169 pata_atiixp firewire_core i2c_algo_bit libahci crc_itu_t pata_via
[ 21.211030]
[ 21.211047] Pid: 812, comm: work_for_cpu Not tainted 2.6.38-7-generic #39-Ubuntu System manufacturer System Product Name/M4A88TD-V EVO/USB3
[ 21.211187] RIP: 0010:[<ffffffffa029e745>] [<ffffffffa029e745>] v4l2_device_register_subdev+0x95/0x170 [videodev]
[ 21.211304] RSP: 0018:ffff880209de5d10 EFLAGS: 00010202
[ 21.211362] RAX: 6564656572662e67 RBX: 00000000ffffffea RCX: ffff88020f38d0c8
[ 21.211438] RDX: ffff88020ea90e40 RSI: ffff88020b5ad380 RDI: ffff88020eb72018
[ 21.211514] RBP: ffff880209de5d40 R08: 0000000000000000 R09: dead000000200200
[ 21.211590] R10: 0000000000000001 R11: 0000000000000001 R12: ffff88020b5ad380
[ 21.211667] R13: ffff88020eb72018 R14: ffffffffa03820e0 R15: ffff88020eb72018
[ 21.211743] FS: 00007f9933fa1720(0000) GS:ffff8800cfc00000(0000) knlGS:0000000000000000
[ 21.211831] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 21.211892] CR2: 000000000048c000 CR3: 000000020fb3b000 CR4: 00000000000006f0
[ 21.211968] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 21.212045] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 21.212121] Process work_for_cpu (pid: 812, threadinfo ffff880209de4000, task ffff88020d2716c0)
[ 21.212214] Stack:
[ 21.212236] ffff880209de5d40 ffffffff8146fc05 ffff88020b097c00 ffff88020b5ad380
[ 21.212318] ffff88020eb72018 ffffffffa03820e0 ffff880209de5d70 ffffffffa028f6b5
[ 21.212401] ffff880209de5d80 0000000000000000 0000000000000042 ffff88020eb52010
[ 21.212484] Call Trace:
[ 21.212513] [<ffffffff8146fc05>] ? i2c_new_device+0x135/0x1c0
[ 21.212578] [<ffffffffa028f6b5>] v4l2_i2c_new_subdev_board+0xf5/0x160 [v4l2_common]
[ 21.212663] [<ffffffffa028f795>] v4l2_i2c_new_subdev+0x75/0xa0 [v4l2_common]
[ 21.215825] [<ffffffffa0333714>] mxb_probe+0x124/0x260 [mxb]
[ 21.219016] [<ffffffffa03345a3>] mxb_attach+0x33/0x1f0 [mxb]
[ 21.220214] [<ffffffffa02e24c7>] saa7146_init_one+0x887/0x13c0 [saa7146]
[ 21.220214] [<ffffffff812fef4f>] local_pci_probe+0x5f/0xd0
[ 21.220214] [<ffffffff8107f890>] ? do_work_for_cpu+0x0/0x30
[ 21.220214] [<ffffffff8107f8a8>] do_work_for_cpu+0x18/0x30
[ 21.220214] [<ffffffff81086fe6>] kthread+0x96/0xa0
[ 21.220214] [<ffffffff8100ce24>] kernel_thread_helper+0x4/0x10
[ 21.220214] [<ffffffff81086f50>] ? kthread+0x0/0xa0
[ 21.220214] [<ffffffff8100ce20>] ? kernel_thread_helper+0x0/0x10
[ 21.220214] Code: f6 74 19 41 83 3e 02 0f 84 eb 00 00 00 49 8b 86 68 02 00 00 65 ff 00 66 66 66 66 90 49 8b 44 24 30 4d 89 6c 24 20 48 85 c0 74 13 <48> 8b 00 48 85 c0 74 0b 4c 89 e7 ff d0 85 c0 89 c3 75 85 49 8b
[ 21.220214] RIP [<ffffffffa029e745>] v4l2_device_register_subdev+0x95/0x170 [videodev]
[ 21.220214] RSP <ffff880209de5d10>
[ 21.260394] ---[ end trace 5adfede4ff2f2907 ]---

2) Another crash, OopsText.txt:

043b
IP: [<ffffffffa014c745>] v4l2_device_register_subdev+0x95/0x170 [videodev]
PGD 0
Oops: 0000 [#1] SMP
last sysfs file: /sys/bus/i2c/drivers/tea6415c/uevent
CPU 0
Modules linked in: tea6415c binfmt_misc tea6420 snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_intel snd_hda_codec snd_hwdep snd_pcm snd_seq_midi snd_rawmidi saa7115 snd_seq_midi_event edac_core edac_mce_amd snd_seq mxb(+) saa7146_vv k10temp saa7146 videobuf_dma_sg videobuf_core asus_atk0110 v4l2_common snd_timer snd_seq_device videodev v4l2_compat_ioctl32 snd soundcore snd_page_alloc sp5100_tco i2c_piix4 xhci_hcd shpchp lp parport usbhid hid sym53c8xx ahci scsi_transport_spi e1000 libahci firewire_ohci r8169 pata_via pata_atiixp firewire_core crc_itu_t

Pid: 589, comm: work_for_cpu Not tainted 2.6.38-7-generic #39-Ubuntu System manufacturer System Product Name/M4A88TD-V EVO/USB3
RIP: 0010:[<ffffffffa014c745>] [<ffffffffa014c745>] v4l2_device_register_subdev+0x95/0x170 [videodev]
RSP: 0018:ffff88020e8dfd10 EFLAGS: 00010202
RAX: 000000000000043b RBX: 00000000ffffffea RCX: ffff88020e889908
RDX: ffff88020aeeb240 RSI: ffff88020f5a8200 RDI: ffff88020ff61a18
RBP: ffff88020e8dfd40 R08: 0000000000000000 R09: 0000000000000002
R10: 0000000000000000 R11: 0000000000000004 R12: ffff88020f5a8200
R13: ffff88020ff61a18 R14: ffffffffa01f10e0 R15: ffff88020ff61a18
FS: 00007f0bb556e720(0000) GS:ffff8800cfc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 000000000000043b CR3: 0000000001a03000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process work_for_cpu (pid: 589, threadinfo ffff88020e8de000, task ffff88020e8cdb00)
Stack:
ffff88020e8dfd40 ffffffff8146fc05 ffff88020691b800 ffff88020f5a8200
ffff88020ff61a18 ffffffffa01f10e0 ffff88020e8dfd70 ffffffffa01726b5
ffff88020e8dfd80 0000000000000000 0000000000000043 ffff88020dac6010
Call Trace:
[<ffffffff8146fc05>] ? i2c_new_device+0x135/0x1c0
[<ffffffffa01726b5>] v4l2_i2c_new_subdev_board+0xf5/0x160 [v4l2_common]
[<ffffffffa0172795>] v4l2_i2c_new_subdev+0x75/0xa0 [v4l2_common]
[<ffffffffa01d06f3>] mxb_probe+0x103/0x260 [mxb]
[<ffffffffa01d15a3>] mxb_attach+0x33/0x1f0 [mxb]
[<ffffffffa01924c7>] saa7146_init_one+0x887/0x13c0 [saa7146]
[<ffffffff812fef4f>] local_pci_probe+0x5f/0xd0
[<ffffffff8107f890>] ? do_work_for_cpu+0x0/0x30
[<ffffffff8107f8a8>] do_work_for_cpu+0x18/0x30
[<ffffffff81086fe6>] kthread+0x96/0xa0
[<ffffffff8100ce24>] kernel_thread_helper+0x4/0x10
[<ffffffff81086f50>] ? kthread+0x0/0xa0
[<ffffffff8100ce20>] ? kernel_thread_helper+0x0/0x10
Code: f6 74 19 41 83 3e 02 0f 84 eb 00 00 00 49 8b 86 68 02 00 00 65 ff 00 66 66 66 66 90 49 8b 44 24 30 4d 89 6c 24 20 48 85 c0 74 13 <48> 8b 00 48 85 c0 74 0b 4c 89 e7 ff d0 85 c0 89 c3 75 85 49 8b
RIP [<ffffffffa014c745>] v4l2_device_register_subdev+0x95/0x170 [videodev]
RSP <ffff88020e8dfd10>
CR2: 000000000000043b
---[ end trace f6215d41cb05d370 ]---


The crashs are on same place, v4l2_device_register_subdev+0x95/0x170

Using the debug symbols of kernel above [1] and source [2], we can see:
(gdb) l *(v4l2_device_register_subdev+0x95)
0x6775 is in v4l2_device_register_subdev (/build/buildd/linux-2.6.38/drivers/media/video/v4l2-device.c:132).
127 /* Warn if we apparently re-register a subdev */
128 WARN_ON(sd->v4l2_dev != NULL);
129 if (!try_module_get(sd->owner))
130 return -ENODEV;
131 sd->v4l2_dev = v4l2_dev;
132 if (sd->internal_ops && sd->internal_ops->registered) {
133 err = sd->internal_ops->registered(sd);
134 if (err)
135 return err;
136 }

So the crash points out to be in dereference of sd->internal_ops, as if
it was sd it would likely crash earlier as sd is used previously in the
code.

And indeed if we look at decodecode of the oops, it matches
sd->internal_ops->registered dereference where the crash happens:

0: f6 74 19 41 divb 0x41(%rcx,%rbx,1)
4: 83 3e 02 cmpl $0x2,(%rsi)
7: 0f 84 eb 00 00 00 je 0xf8
d: 49 8b 86 68 02 00 00 mov 0x268(%r14),%rax
14: 65 ff 00 incl %gs:(%rax)
17: 66 66 66 66 90 data32 data32 data32 xchg %ax,%ax
1c: 49 8b 44 24 30 mov 0x30(%r12),%rax
21: 4d 89 6c 24 20 mov %r13,0x20(%r12)
26: 48 85 c0 test %rax,%rax
29: 74 13 je 0x3e
2b:* 48 8b 00 mov (%rax),%rax <-- trapping instruction
2e: 48 85 c0 test %rax,%rax
31: 74 0b je 0x3e
33: 4c 89 e7 mov %r12,%rdi
36: ff d0 callq *%rax
38: 85 c0 test %eax,%eax
3a: 89 c3 mov %eax,%ebx
3c: 75 85 jne 0xffffffffffffffc3
3e: 49 rex.WB
3f: 8b .byte 0x8b

(gdb) p &((struct v4l2_subdev *)0)->internal_ops
$1 = (const struct v4l2_subdev_internal_ops **) 0x30
(gdb) p &((struct v4l2_subdev_internal_ops *)0)->registered
$2 = (int (**)(struct v4l2_subdev *)) 0x0

So it dereferences and tests successfuly sd->internal_ops:
mov 0x30(%r12),%rax
...
test %rax,%rax
and when it tries to dereference sd->internal_ops->registered it
crashes:
mov (%rax),%rax

But looking at oopses above, look that RAX in each case has a different
value, in first it tries to dereference 0x6564656572662e67, in the other
it is 0x43b instead, so random values in sd->internal_ops

Now wonder why internal_ops got random values. Well, looking back in the
traces, specially at mxb_probe where each crash happens, we can see:

* for the first oops:
(gdb) l *(mxb_probe+0x124)
0x744 is in mxb_probe (/build/buildd/linux-2.6.38/drivers/media/video/mxb.c:197).
192 "tea6420", I2C_TEA6420_2, NULL);
193 mxb->tea6415c = v4l2_i2c_new_subdev(&dev->v4l2_dev, &mxb->i2c_adapter,
194 "tea6415c", I2C_TEA6415C, NULL);
195 mxb->tda9840 = v4l2_i2c_new_subdev(&dev->v4l2_dev, &mxb->i2c_adapter,
196 "tda9840", I2C_TDA9840, NULL);
197 mxb->tuner = v4l2_i2c_new_subdev(&dev->v4l2_dev, &mxb->i2c_adapter,
198 "tuner", I2C_TUNER, NULL);
199
200 /* check if all devices are present */
201 if (!mxb->tea6420_1 || !mxb->tea6420_2 || !mxb->tea6415c ||

* for the second oops:
(gdb) l *(mxb_probe+0x103)
0x723 is in mxb_probe (/build/buildd/linux-2.6.38/drivers/media/video/mxb.c:195).
190 "tea6420", I2C_TEA6420_1, NULL);
191 mxb->tea6420_2 = v4l2_i2c_new_subdev(&dev->v4l2_dev, &mxb->i2c_adapter,
192 "tea6420", I2C_TEA6420_2, NULL);
193 mxb->tea6415c = v4l2_i2c_new_subdev(&dev->v4l2_dev, &mxb->i2c_adapter,
194 "tea6415c", I2C_TEA6415C, NULL);
195 mxb->tda9840 = v4l2_i2c_new_subdev(&dev->v4l2_dev, &mxb->i2c_adapter,
196 "tda9840", I2C_TDA9840, NULL);
197 mxb->tuner = v4l2_i2c_new_subdev(&dev->v4l2_dev, &mxb->i2c_adapter,
198 "tuner", I2C_TUNER, NULL);
199

Hmm the crash seems to be at random, in the cases above probably
when getting tea6415c/tda9840.

Looking at the code then, notice how sd (struct v4l2_subdev *) is
allocated, for example in tda9840_probe we have
sd = kmalloc(sizeof(struct v4l2_subdev), GFP_KERNEL);

So it's not kzalloc, the same holds for tea6415c, its probe function
uses kmalloc as well.

And this is why sd->internal_ops should be getting a random value. I
don't see anywhere in current code where we clear sd->internal_ops on
initialization, and as many of these tuners etc. allocate using just
kmalloc, we get random data in sd.

A fix could be to drivers allocating/zeroing sd using kzalloc/memset
before use.

But seems current v4l code assumes drivers can use kmalloc, and
initialization is done in v4l2_subdev_init, so in a reply to this I
propose a patch to initialize sd->internal_ops to null in
v4l2_subdev_init, which should fix these random crashes.

[1] http://ddebs.ubuntu.com/pool/main/l/linux/linux-image-2.6.38-7-generic-dbgsym_2.6.38-7.39_amd64.ddeb
[2] git://kernel.ubuntu.com/ubuntu/ubuntu-natty.git
(pointing to Ubuntu-2.6.38-7.39 tag checkout)

--
[]'s
Herton


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