linux-kernel - Re: [Ocfs2-devel] [PATCH 1/2] ocfs2: Fix llseek() semantics and do some cleanup

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Date:	Sun, 16 Jun 2013 09:57:24 +0800
From:	shencanquan <shencanquan@...wei.com>
To:	Richard Yao <ryao@...too.org>
CC:	Jeff Liu <jeff.liu@...cle.com>, Mark Fasheh <mfasheh@...e.com>,
	<linux-kernel@...r.kernel.org>, <kernel@...too.org>,
	<linux-fsdevel@...r.kernel.org>,
	Ocfs2-Devel <ocfs2-devel@....oracle.com>
Subject: Re: [Ocfs2-devel] [PATCH 1/2] ocfs2: Fix llseek() semantics and do
 some cleanup

On 2013/6/16 8:44, Richard Yao wrote:
> On 06/15/2013 02:22 AM, shencanquan wrote:
>> Hello, Richard and Jeff,
>>     we found that llseek has another bug when in SEEK_END.  it should be
>> add the inode lock and unlock.
>>     this bug can be reproduce the following scenario:
>>     on one nodeA, open the file and then write some data to file and
>> close the file .
>>     on  another nodeB , open the file and llseek the end of file . the
>> position of file is old.
> Did these operations occur sequentially or did they occur concurrently?
>
> If you meant the former, the inode cache is not being invalidated. That
> should be a bug because Oracle claims OCFS2 is cache-coherent. However,
> it is possible that this case was left out of the cache-coherence
> protocol for performance purposes. If that is the case, then this would
> be by design. someone who works for Oracle would need to comment on that
> though.

    it is a occur sequentially.  after close the file on NodeA , on 
nodeB and then open the file and llseek the end of file.

>
> If you meant the latter, you should ask yourself what would happen when
> you run two separate programs on the same file in a local filesystem.
> There should be no way to avoid a race without some kind of a locking
> mechanism.
>


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