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

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Date:   Fri, 10 Aug 2018 09:05:26 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.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 08/10/2018 09:02 AM, Darrick J. Wong wrote:
> 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. :)

For the conflict part yes. Thanks! :)

> 
> --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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