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Date:   Tue, 14 Jan 2020 11:39:36 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH V2 10/12] fs/xfs: Fix truncate up

On Tue, Jan 14, 2020 at 11:00:57AM -0800, 'Ira Weiny' wrote:
> On Mon, Jan 13, 2020 at 05:14:07PM -0800, Darrick J. Wong wrote:
> > On Mon, Jan 13, 2020 at 04:40:47PM -0800, Ira Weiny wrote:
> > > On Mon, Jan 13, 2020 at 02:27:55PM -0800, Darrick J. Wong wrote:
> > > > On Fri, Jan 10, 2020 at 11:29:40AM -0800, ira.weiny@...el.com wrote:
> > > > > From: Ira Weiny <ira.weiny@...el.com>

[snip]

> 
> > 
> > > But as I said in the cover I am not 100% sure of
> > > this fix.
> > 
> > > From what I can tell xfs_ioctl_setattr_dax_invalidate() should invalidate the
> > > mappings and the page cache and the traces I have indicate that the DAX mode
> > > is not changing or was properly held off.
> > 
> > Hmm, that implies the invalidation didn't work.  Can you find a way to
> > report the contents of the page cache after the dax mode change
> > invalidation fails?  I wonder if this is something dorky like rounding
> > down such that the EOF page doesn't actually get invalidated?
> > 
> > Hmm, no, xfs_ioctl_setattr_dax_invalidate should be nuking all the
> > pages... do you have a quick reproducer?
> 
> I thought I did...
> 
> What I have done is take this patch:
> 
> https://www.spinics.net/lists/fstests/msg13313.html
> 
> and put [run_fsx ""] in a loop... (diff below) And without this truncate fix
> patch it was failing in about 5 - 10 iterations.  But I'm running it right now
> and it has gone for 30+...  :-(

Ok...  perhaps this is a qemu problem?  In qemu I had a slightly different
script; 'test-suite.sh' (attached).  This was copied to create the xfstest I
sent.  Without this 'fix truncate patch I get something like the following
after in just a few iterations.

...

   *** run 'fsx ' racing with setting/clearing the DAX flag
   *** run 'fsx ' racing with setting/clearing the DAX flag
FAILED: fsx exited with status : 205
        see trace_output
zero_range to largest ever: 0x19867
truncating to largest ever: 0x3fb6d
zero_range to largest ever: 0x40000
Mapped Write: non-zero data past EOF (0x3ab88) page offset 0xb89 is 0xe71c
LOG DUMP (15817 total operations):
15818(202 mod 256): SKIPPED (no operation)
15819(203 mod 256): ZERO     0x2ae9f thru 0x3346c       (0x85ce bytes)
15820(204 mod 256): READ     0x3637 thru 0x91e6 (0x5bb0 bytes)
15821(205 mod 256): MAPREAD  0x38a80 thru 0x3d014       (0x4595 bytes)
15822(206 mod 256): INSERT 0x28000 thru 0x29fff (0x2000 bytes)

Ira

> 
> I am 90% confident that this series works for 100% of the use cases we have.  I
> think this is an existing bug which I've just managed to find.  And again I'm
> not comfortable with this patch either.  So I'm not trying to argue for it but
> I just don't know what could be wrong...
> 
> Ira
> 
> diff --git a/tests/generic/999 b/tests/generic/999
> index 6dd5529dbc65..929c20c6db04 100755
> --- a/tests/generic/999
> +++ b/tests/generic/999
> @@ -274,7 +274,9 @@ function run_fsx {
>         pid=""
>  }
>  
> -run_fsx ""
> +while [ 1 ]; do
> +       run_fsx ""
> +done
>  run_fsx "-A"
>  run_fsx "-Z -r 4096 -w 4096"
> 

View attachment "test-suite.sh" of type "text/plain" (7345 bytes)

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