linux-kernel - Re: 2.6.18 ext3 panic.

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Message-ID: <452EB9C5.4000404@us.ibm.com>
Date:	Thu, 12 Oct 2006 14:55:17 -0700
From:	Badari Pulavarty <pbadari@...ibm.com>
To:	Eric Sandeen <esandeen@...hat.com>
CC:	Andrew Morton <akpm@...l.org>, Jan Kara <jack@...e.cz>,
	Eric Sandeen <sandeen@...deen.net>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.18 ext3 panic.

Eric Sandeen wrote:
> Andrew Morton wrote:
>
>   
>> On Thu, 12 Oct 2006 14:28:20 +0200
>> Jan Kara <jack@...e.cz> wrote:
>>
>>   
>>     
>>> Where can we call
>>> journal_dirty_data() without PageLock?
>>>     
>>>       
>> block_write_full_page() will unlock the page, so ext3_writepage()
>> will run journal_dirty_data_fn() against an unlocked page.
>>
>> I haven't looked into the exact details of the race, but it should
>> be addressable via jbd_lock_bh_state() or j_list_lock coverage
>>     
> I'm testing with something like this now; seem sane?
>
> journal_dirty_data & journal_unmap_data both check do 
> jbd_lock_bh_state(bh) close to the top... journal_dirty_data_fn has checked 
> buffer_mapped before getting into journal_dirty_data, but that state may
> change before the lock is grabbed.  Similarly re-check after we drop the lock.
>
>   
This is exactly  the solution I proposed earlier (to check 
buffer_mapped() before calling submit_bh()).
But at that time, Jan pointed out that the whole handling is wrong.

But if this is the only case we need to handle, I am okay with this band 
aid :)

Thanks,
Badari

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