Date:	Tue, 18 Jan 2011 17:14:03 +0100
From:	Patrik Jakobsson <patrik.r.jakobsson@...il.com>
To:	Rune Saetre <rune.saetre@...omar.com>
CC:	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: PROBLEM: kernel BUG at drivers/media/video/em28xx/em28xx-video.c:891

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?

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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