Date:	Fri, 12 Jul 2013 22:56:44 +0200
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	Hans Verkuil <hverkuil@...all.nl>
CC:	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...hat.com>
Subject: Re: [media] cx25821 regression from 3.9: BUG: bad unlock balance detected!


Friday, May 17, 2013, 11:52:17 AM, you wrote:

> On Fri May 17 2013 11:04:50 Sander Eikelenboom wrote:
>> 
>> Friday, May 17, 2013, 10:25:24 AM, you wrote:
>> 
>> > On Thu May 16 2013 19:41:42 Sander Eikelenboom wrote:
>> >> Hi Hans / Mauro,
>> >> 
>> >> With 3.10.0-rc1 (including the cx25821 changes from Hans), I get the bug below which wasn't present with 3.9.
>> 
>> > How do I reproduce this? I've tried to, but I can't make this happen.
>> 
>> > Looking at the code I can't see how it could hit this bug anyway.
>> 
>> I'm using "motion" to grab and process 6 from the video streams of the card i have (card with 8 inputs).
>> It seems the cx25821 underwent quite some changes between 3.9 and 3.10.

> It did.

>> And in the past there have been some more locking issues around mmap and media devices, although they seem to appear as circular locking dependencies and with different devices.
>>    - http://www.mail-archive.com/linux-media@vger.kernel.org/msg46217.html
>>    - Under kvm: http://www.spinics.net/lists/linux-media/msg63322.html

> Neither of those are related to this issue.

>> 
>> - Perhaps that running in a VM could have to do with it ?
>>    - The driver on 3.9 occasionaly gives this, probably latency related (but continues to work):
>>      cx25821: cx25821_video_wakeup: 2 buffers handled (should be 1)
>> 
>>      Could it be something double unlocking in that path ?
>> 
>> - Is there any extra debugging i could enable that could pinpoint the issue ?

> Try this patch:

> diff --git a/drivers/media/pci/cx25821/cx25821-core.c b/drivers/media/pci/cx25821/cx25821-core.c
> index b762c5b..8f8d0e0 100644
> --- a/drivers/media/pci/cx25821/cx25821-core.c
> +++ b/drivers/media/pci/cx25821/cx25821-core.c
> @@ -1208,7 +1208,6 @@ void cx25821_free_buffer(struct videobuf_queue *q, struct cx25821_buffer *buf)
>         struct videobuf_dmabuf *dma = videobuf_to_dma(&buf->vb);
>  
>         BUG_ON(in_interrupt());
> -       videobuf_waiton(q, &buf->vb, 0, 0);
>         videobuf_dma_unmap(q->dev, dma);
>         videobuf_dma_free(dma);
>         btcx_riscmem_free(to_pci_dev(q->dev), &buf->risc);

> I don't think the waiton is really needed for this driver.

> What really should happen is that videobuf is replaced by videobuf2 in this
> driver, but that's a fair amount of work.

Hi Hans,

After being busy for quite some time, i do have some spare time now.

Since i'm still having trouble with this driver, is there a patch series for a similar driver
that was converted to videobuf2 ?
I don't know if it is entirely in my league, but i could give it a try when i have a example.

--
Sander


> Regards,

>         Hans

>> 
>> 
>> --
>> 
>> Sander
>> 
>> 
>> 
>> > Regards,
>> 
>> >         Hans
>> 
>> >> 
>> >> --
>> >> Sander
>> >> 
>> >> 
>> >> [   53.004968] =====================================
>> >> [   53.004968] [ BUG: bad unlock balance detected! ]
>> >> [   53.004968] 3.10.0-rc1-20130516-jens+ #1 Not tainted
>> >> [   53.004968] -------------------------------------
>> >> [   53.004968] motion/3328 is trying to release lock (&dev->lock) at:
>> >> [   53.004968] [<ffffffff819be5f9>] mutex_unlock+0x9/0x10
>> >> [   53.004968] but there are no more locks to release!
>> >> [   53.004968]
>> >> [   53.004968] other info that might help us debug this:
>> >> [   53.004968] 1 lock held by motion/3328:
>> >> [   53.004968]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff81156cae>] vm_munmap+0x3e/0x70
>> >> [   53.004968]
>> >> [   53.004968] stack backtrace:
>> >> [   53.004968] CPU: 1 PID: 3328 Comm: motion Not tainted 3.10.0-rc1-20130516-jens+ #1
>> >> [   53.004968] Hardware name: Xen HVM domU, BIOS 4.3-unstable 05/16/2013
>> >> [   53.004968]  ffffffff819be5f9 ffff88002ac35c58 ffffffff819b9029 ffff88002ac35c88
>> >> [   53.004968]  ffffffff810e615e ffff88002ac35cb8 ffff88002b7c18a8 ffffffff819be5f9
>> >> [   53.004968]  00000000ffffffff ffff88002ac35d28 ffffffff810eb17e ffffffff810e7ba5
>> >> [   53.004968] Call Trace:
>> >> [   53.004968]  [<ffffffff819be5f9>] ? mutex_unlock+0x9/0x10
>> >> [   53.004968]  [<ffffffff819b9029>] dump_stack+0x19/0x1b
>> >> [   53.004968]  [<ffffffff810e615e>] print_unlock_imbalance_bug+0xfe/0x110
>> >> [   53.004968]  [<ffffffff819be5f9>] ? mutex_unlock+0x9/0x10
>> >> [   53.004968]  [<ffffffff810eb17e>] lock_release_non_nested+0x1ce/0x320
>> >> [   53.004968]  [<ffffffff810e7ba5>] ? debug_check_no_locks_freed+0x105/0x1b0
>> >> [   53.353529]  [<ffffffff819be5f9>] ? mutex_unlock+0x9/0x10
>> >> [   53.353529]  [<ffffffff810eb3cc>] lock_release+0xfc/0x250
>> >> [   53.353529]  [<ffffffff819be4b2>] __mutex_unlock_slowpath+0xb2/0x1f0
>> >> [   53.353529]  [<ffffffff819be5f9>] mutex_unlock+0x9/0x10
>> >> [   53.353529]  [<ffffffff81711105>] videobuf_waiton+0x55/0x230
>> >> [   53.353529]  [<ffffffff8114d052>] ? tlb_finish_mmu+0x32/0x50
>> >> [   53.353529]  [<ffffffff81154a46>] ? unmap_region+0xc6/0x100
>> >> [   53.353529]  [<ffffffff81172e05>] ? kmem_cache_free+0x195/0x230
>> >> [   53.353529]  [<ffffffff8172d3d9>] cx25821_free_buffer+0x49/0xa0
>> >> [   53.353529]  [<ffffffff8172f939>] cx25821_buffer_release+0x9/0x10
>> >> [   53.353529]  [<ffffffff81712c35>] videobuf_vm_close+0xc5/0x160
>> >> [   53.353529]  [<ffffffff81154aa5>] remove_vma+0x25/0x60
>> >> [   53.353529]  [<ffffffff81156b67>] do_munmap+0x307/0x410
>> >> [   53.353529]  [<ffffffff81156cbc>] vm_munmap+0x4c/0x70
>> >> [   53.353529]  [<ffffffff81157c09>] SyS_munmap+0x9/0x10
>> >> [   53.353529]  [<ffffffff819c20a9>] system_call_fastpath+0x16/0x1b
>> >> 
>> 
>> 


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