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Re: [BUG] ext2/3/4: dio reads stale data when we do some append dio writ

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
Subject: Re: [BUG] ext2/3/4: dio reads stale data when we do some append dio writes
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 19 Nov 2013 23:09:29 +1100
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20131119115122.GC4782@xxxxxxxxx>
References: <20131119095302.GA4534@xxxxxxxxx> <20131119102235.GA5010@xxxxxxxxxxxxx> <20131119104508.GA4630@xxxxxxxxx> <20131119110147.GA3323@xxxxxxxxxxxxx> <20131119111947.GA4782@xxxxxxxxx> <20131119111826.GA20485@xxxxxxxxxxxxx> <20131119115122.GC4782@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Nov 19, 2013 at 07:51:22PM +0800, Zheng Liu wrote:
> On Tue, Nov 19, 2013 at 03:18:26AM -0800, Christoph Hellwig wrote:
> > On Tue, Nov 19, 2013 at 07:19:47PM +0800, Zheng Liu wrote:
> > > Yes, I know that XFS has a shared/exclusive lock.  I guess that is why
> > > it can pass the test.  But another question is why xfs fails when we do
> > > some append dio writes with doing buffered read.
> > 
> > Can you provide a test case for that issue?
> 
> Simple.  Reader just need to open this file without O_DIRECT flag.  I
> paste the full code snippet below.  Please take care of this line:
>       readfd = open(argv[1], /*O_DIRECT|*/O_RDONLY, S_IRWXU);
> 
> The result of this program on my own sand box looks like below:
>         encounter an error: offset 0
....
>               if (ret >= 0) {
>                       for (j = 0; j < ret; j++) {
>                               if (rbuf[i] != 'a') {
>                                       fprintf(stderr, "encounter an error: 
> offset %ld\n",
>                                               i);
>                                       goto err;

Should be checking rbuf[j], perhaps?

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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