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SubjectRe: PROBLEM: kernel BUG at drivers/media/video/em28xx/em28xx-video.c:891
On 01/18/2011 05:30 PM, Hans Verkuil wrote:
> On Tuesday, January 18, 2011 17:14:03 Patrik Jakobsson wrote:
>> Hello Rune
>>
>> I'm trying to learn more about the linux kernel so I figured helping
>> with bugs is a good way to get started.
>>
>> On 01/18/2011 02:20 AM, Rune Saetre wrote:
>>> Hi
>>>
>>> The crash is not as consistent as I first believed. I have managed to
>>> stop and start capturing several (but not many) times without the
>>> driver crashing now.
>>>
>> To me it seems that the resource locking (functions res_get, res_check,
>> res_locked and res_free) is subject to race condition.
>>
>> I looked at older versions of the code and found that there used to be
>> locks around some of these pieces. It was removed in commit:
>>
>> 0499a5aa777f8e56e46df362f0bb9d9d116186f9 - V4L/DVB: em28xx: remove BKL
>>
>> Other V4L drivers use pretty much the same code (res_get, res_free,
>> etc.) for resource locking but still have the mutex_lock/unlock around
>> it. Does anyone know why this was removed?
> Because now the video4linux core does the locking.
>
> Anyway, I'm pretty sure this is the bug that was fixed here:
>
> http://www.mail-archive.com/linuxtv-commits@linuxtv.org/msg09413.html
>
> This fix will be in 2.6.38.
>
> The change in the locking mechanism had nothing to do this particular bug.
> It was just incorrect administration of resources.
>
> Regards,
>
> Hans
>
Thanks for the explanation. I see now how the V4L core locks around the
ioctls. The member unlocked_ioctl of struct v4l2_file_operations
confused me a little. Maybe serialized_ioctl would be a better name? Not
a big issue though.

Hopefully the patch fixes your problem Rune.

Thanks
Patrik Jakobsson

>> Thanks
>> Patrik Jakobsson
>>> The trace logs also differ slightly. Here is the last one:
>>>
>>> Jan 18 02:12:08 mate kernel: [ 117.219326] ------------[ cut here
>>> ]------------
>>> Jan 18 02:12:08 mate kernel: [ 117.219412] kernel BUG at
>>> drivers/media/video/em28xx/em28xx-video.c:891!
>>> Jan 18 02:12:08 mate kernel: [ 117.219507] invalid opcode: 0000 [#1]
>>> PREEMPT SMP Jan 18 02:12:08 mate kernel: [ 117.219597] last sysfs
>>> file: /sys/devices/virtual/block/dm-8/stat
>>> Jan 18 02:12:08 mate kernel: [ 117.219681] CPU 1 Jan 18 02:12:08 mate
>>> kernel: [ 117.219714] Modules linked in: acpi_cpufreq mperf
>>> cpufreq_powersave cpufreq_stats cpufreq_userspace cpufreq_conservative
>>> ppdev lp nfsd lockd nfs_acl auth_rpcgss sunrpc exportfs binfmt_misc
>>> fuse dummy bridge stp ext2 mbcache coretemp kvm_intel kvm loop
>>> firewire_sbp2 tuner snd_hda_codec_realtek arc4 snd_hda_intel
>>> snd_usb_audio snd_hda_codec ecb snd_seq_dummy snd_pcm_oss
>>> snd_mixer_oss saa7115 snd_pcm ir_lirc_codec lirc_dev ir_sony_decoder
>>> snd_hwdep snd_usbmidi_lib em28xx ir_jvc_decoder ir_rc6_decoder
>>> snd_seq_oss snd_seq_midi snd_rawmidi r8169 ir_rc5_decoder mii
>>> ir_nec_decoder snd_seq_midi_event i915 v4l2_common iwlagn iwlcore
>>> snd_seq ir_core drm_kms_helper drm videobuf_vmalloc snd_timer
>>> snd_seq_device videobuf_core pcmcia joydev mac80211 uvcvideo videodev
>>> v4l1_compat v4l2_compat_ioctl32 tveeprom cfg80211 rfkill i2c_i801
>>> i2c_algo_bit tpm_tis tpm yenta_socket snd intel_agp shpchp pci_hotplug
>>> video output pcmcia_rsrc wmi pcmcia_core soundcore snd_page_alloc
>>> parport_pc parport i2c_cor
>>> Jan 18 02:12:08 mate kernel: irda tpm_bios intel_gtt pcspkr crc_ccitt
>>> psmouse evdev serio_raw container processor battery ac button reiserfs
>>> dm_mod raid10 raid456 async_raid6_recov async_pq raid6_pq async_xor
>>> xor async_memcpy async_tx raid1 raid0 multipath linear md_mod
>>> ide_cd_mod cdrom sd_mod ata_generic pata_acpi ata_piix crc_t10dif
>>> ide_pci_generic ahci libahci sdhci_pci firewire_ohci sdhci libata
>>> scsi_mod piix ide_core firewire_core mmc_core uhci_hcd tg3 thermal
>>> crc_itu_t thermal_sys ehci_hcd [last unloaded: scsi_wait_scan]
>>> Jan 18 02:12:08 mate kernel: [ 117.220091] Jan 18 02:12:08 mate
>>> kernel: [ 117.220091] Pid: 3154, comm: camera_factory_ Not tainted
>>> 2.6.37-rst #1 Victoria /TravelMate 6292 Jan 18 02:12:08 mate
>>> kernel: [ 117.220091] RIP: 0010:[<ffffffffa05a37f4>]
>>> [<ffffffffa05a37f4>] res_free+0x14/0x49 [em28xx]
>>> Jan 18 02:12:08 mate kernel: [ 117.220091] RSP:
>>> 0018:ffff8800794a1c48 EFLAGS: 00010297
>>> Jan 18 02:12:08 mate kernel: [ 117.220091] RAX: 0000000000000001 RBX:
>>> ffff88007b94dc00 RCX: 0000000000000000
>>> Jan 18 02:12:08 mate kernel: [ 117.220091] RDX: 0000000000000000 RSI:
>>> ffff8800378e7000 RDI: ffff88007b94dc00
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] RBP: ffff8800378e7000 R08:
>>> 0000000000000001 R09: 0000000000000c52
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] R10: 0000000000000000 R11:
>>> 0000000000000246 R12: 0000000000000000
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] R13: ffffffffa05ab920 R14:
>>> ffff88006dd123c0 R15: ffff88007b94dc00
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] FS:
>>> 00007f37105bb820(0000) GS:ffff88007f500000(0000) knlGS:0000000000000000
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] CS: 0010 DS: 0000 ES:
>>> 0000 CR0: 0000000080050033
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] CR2: 000000000378b248 CR3:
>>> 000000007a079000 CR4: 00000000000006e0
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] DR0: 0000000000000000 DR1:
>>> 0000000000000000 DR2: 0000000000000000
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] DR3: 0000000000000000 DR6:
>>> 00000000ffff0ff0 DR7: 0000000000000400
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] Process camera_factory_
>>> (pid: 3154, threadinfo ffff8800794a0000, task ffff880071f6d820)
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] Stack:
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] ffff8800378e7000
>>> ffffffffa05a46b9 ffff88007a2fd040 ffffffff81042cf3
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] 0000000000000001
>>> ffffffff00000001 ffffffff8103dadb 0000000000000001
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] ffff88007ba3e400
>>> ffffffffa03302ff 00000000000135c0 00000000000135c0
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] Call Trace:
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffffa05a46b9>] ?
>>> vidioc_streamoff+0xa6/0xb6 [em28xx]
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff81042cf3>] ?
>>> get_parent_ip+0x9/0x1b
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff8103dadb>] ?
>>> need_resched+0x1a/0x23
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffffa03302ff>] ?
>>> __video_do_ioctl+0x12e2/0x33a0 [videodev]
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff8103a5fe>] ?
>>> __wake_up_common+0x41/0x78
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff8103da1b>] ?
>>> __wake_up+0x35/0x46
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff81042cf3>] ?
>>> get_parent_ip+0x9/0x1b
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff81044d80>] ?
>>> add_preempt_count+0x9e/0xa0
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff8132935c>] ?
>>> _raw_spin_lock_irqsave+0x40/0x61
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffffa03326f4>] ?
>>> video_ioctl2+0x2ad/0x35d [videodev]
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff81042cf3>] ?
>>> get_parent_ip+0x9/0x1b
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffffa032e342>] ?
>>> v4l2_ioctl+0x74/0x113 [videodev]
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff81106f51>] ?
>>> do_vfs_ioctl+0x418/0x465
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff81106fda>] ?
>>> sys_ioctl+0x3c/0x5e
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] [<ffffffff81009c52>] ?
>>> system_call_fastpath+0x16/0x1b
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] Code: 03 4c 39 e3 0f 18 08
>>> 75 d4 31 c0 eb 05 b8 ea ff ff ff 5b 5d 41 5c c3 48 83 ec 08 8b 57 0c
>>> 89 f0 89 c1 48 8b 37 21 d1 39 c1 74 04<0f> 0b eb fe 89 c8 f7 d0 21 c2
>>> 89 57 0c 21 86 d0 09 00 00 83 3d Jan 18 02:12:09 mate kernel: [
>>> 117.220091] RIP [<ffffffffa05a37f4>] res_free+0x14/0x49 [em28xx]
>>> Jan 18 02:12:09 mate kernel: [ 117.220091] RSP<ffff8800794a1c48>
>>> Jan 18 02:12:09 mate kernel: [ 117.264998] ---[ end trace
>>> 6d6576ecd99356c8 ]---
>>>
>>> I hope this helps.
>>>
>>> Regards
>>> Rune
>>>
>>>
>> --
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