linux-ext4 - Re: [PATCH 2/2] [PATCH] xfs: Close race between direct IO and xfs_break

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Date:   Wed, 8 Aug 2018 08:47:39 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     tytso@....edu, darrick.wong@...cle.com, zwisler@...nel.org,
        linux-nvdimm@...ts.01.org, david@...morbit.com,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        lczerner@...hat.com, linux-ext4@...r.kernel.org, hch@....de
Subject: Re: [PATCH 2/2] [PATCH] xfs: Close race between direct IO and
 xfs_break_layouts()



On 08/08/2018 01:53 AM, Jan Kara wrote:
> On Tue 07-08-18 15:11:43, Dave Jiang wrote:
>> This patch is the duplicate of ross's fix for ext4 for xfs.
>>
>> If the refcount of a page is lowered between the time that it is returned
>> by dax_busy_page() and when the refcount is again checked in
>> xfs_break_layouts() => ___wait_var_event(), the waiting function
>> xfs_wait_dax_page() will never be called.  This means that
>> xfs_break_layouts() will still have 'retry' set to false, so we'll stop
>> looping and never check the refcount of other pages in this inode.
>>
>> Instead, always continue looping as long as dax_layout_busy_page() gives us
>> a page which it found with an elevated refcount.
>>
>> Signed-off-by: Dave Jiang <dave.jiang@...el.com>
> 
> The patch looks good to me. You can add:
> 
> Reviewed-by: Jan Kara <jack@...e.cz>
> 
> Just one minor nit below:
> 
>> @@ -746,9 +744,10 @@ xfs_break_dax_layouts(
>>  	if (!page)
>>  		return 0;
>>  
>> +	*did_unlock = true;
> 
> I think it would be more understandable to name the argument of
> xfs_break_dax_layouts() as 'retry' instead of 'did_unlock' as it's not
> about unlocking anymore.

Thanks for the review Jan! I will change. I was trying to decide between
less code change vs more clear definition. :)

> 
> 							Honza
>