linux-ext4 - Re: [PATCH v2 2/2] [PATCH] xfs: Close race between direct IO and xfs_break

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Message-ID: <20180810160243.GF4203@magnolia>
Date:   Fri, 10 Aug 2018 09:02:43 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     tytso@....edu, 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 v2 2/2] [PATCH] xfs: Close race between direct IO and
 xfs_break_layouts()

On Fri, Aug 10, 2018 at 08:54:00AM -0700, Dave Jiang wrote:
> 
> 
> On 08/10/2018 08:48 AM, Darrick J. Wong wrote:
> > On Wed, Aug 08, 2018 at 10:31:40AM -0700, 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>
> >> Reviewed-by: Jan Kara <jack@...e.cz>
> >> ---
> >>
> >> Sorry resend, forgot to add Jan's reviewed-by.
> >>
> >> v2:
> >> - Rename parameter from did_unlock to retry (Jan)
> >>
> >>  fs/xfs/xfs_file.c |    9 ++++-----
> >>  1 file changed, 4 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> >> index a3e7767a5715..cd6f0d8c4922 100644
> >> --- a/fs/xfs/xfs_file.c
> >> +++ b/fs/xfs/xfs_file.c
> >> @@ -721,12 +721,10 @@ xfs_file_write_iter(
> >>  
> >>  static void
> >>  xfs_wait_dax_page(
> >> -	struct inode		*inode,
> >> -	bool			*did_unlock)
> >> +	struct inode		*inode)
> >>  {
> >>  	struct xfs_inode        *ip = XFS_I(inode);
> >>  
> >> -	*did_unlock = true;
> >>  	xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
> >>  	schedule();
> >>  	xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
> >> @@ -736,7 +734,7 @@ static int
> >>  xfs_break_dax_layouts(
> >>  	struct inode		*inode,
> >>  	uint			iolock,
> >> -	bool			*did_unlock)
> >> +	bool			*retry)
> > 
> > Uhhh, this hunk doesn't apply.  xfs_break_dax_layouts doesn't have an
> > iolock parameter anymore; was this not generated off of xfs for-next?
> 
> Sorry. It was generated against 4.18-rc8. I'll respin patch against xfs
> for-next.

I think it's just a matter of taking the old patch and changing
"did_unlock" to "retry", right?  If so, I'll just change that and be
done with this one. :)

--D

> > 
> > --D
> > 
> >>  {
> >>  	struct page		*page;
> >>  
> >> @@ -746,9 +744,10 @@ xfs_break_dax_layouts(
> >>  	if (!page)
> >>  		return 0;
> >>  
> >> +	*retry = true;
> >>  	return ___wait_var_event(&page->_refcount,
> >>  			atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
> >> -			0, 0, xfs_wait_dax_page(inode, did_unlock));
> >> +			0, 0, xfs_wait_dax_page(inode));
> >>  }
> >>  
> >>  int
> >>
> >> --
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