linux-ext4 - Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict

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Date:	Fri, 26 Aug 2011 17:03:14 +0800
From:	Tao Ma <tm@....ma>
To:	Dave Chinner <david@...morbit.com>
CC:	Theodore Ts'o <tytso@....edu>, Jiaying Zhang <jiayingz@...gle.com>,
	linux-ext4@...r.kernel.org
Subject: Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict_inode()

On 08/26/2011 04:44 PM, Dave Chinner wrote:
> On Fri, Aug 26, 2011 at 05:35:07PM +1000, Dave Chinner wrote:
>> On Thu, Aug 25, 2011 at 11:33:44PM -0400, Theodore Ts'o wrote:
>>>
>>> Note: this will probably need to be sent to Linus as an emergency
>>> bugfix ASAP, since it was introduced in 3.1-rc1, so it represents a
>>> regression.
>>
>> It doesn't appear to be a bug. All of the new ext4 lockdep reports
>> in 3.1 I've seen (except for the mmap_sem/i_mutex one) are false
>> positives....
> 
> While the lockdep report is false positive, I agree that your
> change is the right fix to make - the IO completions are already
> queued on the workqueue, so they don't need to be flushed to get
> them to complete. All that needs to be done is call
> ext4_ioend_wait() for them to complete, and that gets rid of the
> i_mutex altogether. (*)
ext4_ioend_wait can't work here for a nasty bug. Please see the commit
log of 2581fdc8.

Thanks
Tao
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