linux-ext4 - Re: [PATCH RESEND v2] ext4: Close race between direct IO and ext4_break

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Date:   Tue, 11 Sep 2018 15:31:47 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     Dave Jiang <dave.jiang@...el.com>, zwisler@...nel.org,
        linux-ext4@...r.kernel.org, lczerner@...hat.com,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH RESEND v2] ext4: Close race between direct IO and
 ext4_break_layouts()

On Tue, Sep 11, 2018 at 05:25:50PM +0200, Jan Kara wrote:
> From: Ross Zwisler <zwisler@...nel.org>
> 
> 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
> ext4_break_layouts() => ___wait_var_event(), the waiting function
> ext4_wait_dax_page() will never be called.  This means that
> ext4_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: Ross Zwisler <ross.zwisler@...ux.intel.com>
> Reviewed-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Jan Kara <jack@...e.cz>

Applied, thanks.

						- Ted