xfs: Close race between direct IO and xfs_break_layouts()

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@intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 4 insertions, 5 deletions

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 6b31f41eafa2..181e9084519b 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);
@@ -735,7 +733,7 @@ xfs_wait_dax_page(
 static int
 xfs_break_dax_layouts(
         struct inode            *inode,
-        bool                    *did_unlock)
+        bool                    *retry)
 {
         struct page             *page;
 
@@ -745,9 +743,10 @@ 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