On 08/10/2018 11:31 AM, Eric Sandeen wrote:
> On 8/8/18 12:31 PM, 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.
>
> Hi Dave, does this have a testcase? Have you seen the issue using Ross's
> xfstest generic/503 or is there some other test? Apologies if I missed
> prior discussion on a testcase or race frequency...
I do not have a testcase. I know Ross replicated it on ext4. And Jan
asked to create the same fix with XFS when he reviewed Ross's fix for ext4.
>
> Thanks,
> -Eric
>
>> Signed-off-by: Dave Jiang <dave.jiang@xxxxxxxxx>
>> Reviewed-by: Jan Kara <jack@xxxxxxx>
>> ---
>>
>> 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)
>> {
>> 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
>>
