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 10:53:39 +0200
From:   Jan Kara <jack@...e.cz>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     tytso@....edu, darrick.wong@...cle.com, jack@...e.cz,
        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 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.

							Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR