Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict_inode()

From: Jiaying Zhang <jiayingz@google.com>
To: "Ted Ts'o" <tytso@mit.edu>
Cc: Tao Ma <tm@tao.ma>, Dave Chinner <david@fromorbit.com>,
	linux-ext4@vger.kernel.org
Subject: Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict_inode()
Date: Tue, 30 Aug 2011 18:15:23 -0700	[thread overview]
Message-ID: <CAFgt=MBOnhCQG+dmHa1crFKU4+XL6RyihnMq=-O8UuK4yEEXnA@mail.gmail.com> (raw)
In-Reply-To: <CAFgt=MA+YokAz4Nzd+OFk7XTDYXMbjXv8G_oXFieDMDr-u4RAg@mail.gmail.com>

FYI, I just sent out a patch to the linux-ext4@ that uses
mutex_trylock() in ext4_end_io_work() and removes the i_mutex
lock and ext4_flush_completed_IO() in ext4_evict_inode():
http://www.spinics.net/lists/linux-ext4/msg27407.html

Jiaying

On Fri, Aug 26, 2011 at 10:17 PM, Jiaying Zhang <jiayingz@google.com> wrote:
> On Fri, Aug 26, 2011 at 1:22 PM, Ted Ts'o <tytso@mit.edu> wrote:
>> On Fri, Aug 26, 2011 at 09:58:45AM -0700, Jiaying Zhang wrote:
>>> Now thinking about an alternative approach to resolve the deadlock
>>> mentioned above, maybe we can use mutex_trylock() in
>>> ext4_end_io_work() and if we can't grab the mutex lock for an inode,
>>> just requeue the work to the end of workqueue?
>>
>> Good idea!  That should speed up work queue processing in general, I
>> think.
>>
>> The downside is that inodes that currently locked might take longer to
>> complete.  In the case of fsync() we'll just force the I/O completion
>> to happen in the context of the fsync'ing process, so I don't think it
>> should be a problem in practice I think.
>>
> Ted,
>
> I am working on a patch to use mutex_trylock() in ext4_end_io_work()
> so that we can fix the described deadlock without needing to call
> mutex_lock() and  ext4_flush_completed_IO() in ext4_evict_inode().
> I run into some problem while testing it. Given that the deadlock my
> original patch intended to fix only exists with dioread_nolock enabled
> but the lockdep issue happens in all of cases, I think we should roll
> that part back as you have planned. I am going to send a separate patch
> later to fix the deadlock issue once I resolved the problem found in
> my test.
>
> Jiaying
>
>>                                        - Ted
>>
>
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