xfs: force writes to delalloc regions to unwritten

When writing to a delalloc region in the data fork, commit the new
allocations (of the da reservation) as unwritten so that the mappings
are only marked written once writeback completes successfully.  This
fixes the problem of stale data exposure if the system goes down during
targeted writeback of a specific region of a file, as tested by
generic/042.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 18 insertions, 11 deletions

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index d3faa91369bf..b4acb032cdbe 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -4053,17 +4053,7 @@ xfs_bmapi_allocate(
 	bma->got.br_blockcount = bma->length;
 	bma->got.br_state = XFS_EXT_NORM;
 
-	/*
-	 * In the data fork, a wasdelay extent has been initialized, so
-	 * shouldn't be flagged as unwritten.
-	 *
-	 * For the cow fork, however, we convert delalloc reservations
-	 * (extents allocated for speculative preallocation) to
-	 * allocated unwritten extents, and only convert the unwritten
-	 * extents to real extents when we're about to write the data.
-	 */
-	if ((!bma->wasdel || (bma->flags & XFS_BMAPI_COWFORK)) &&
-	    (bma->flags & XFS_BMAPI_PREALLOC))
+	if (bma->flags & XFS_BMAPI_PREALLOC)
 		bma->got.br_state = XFS_EXT_UNWRITTEN;
 
 	if (bma->wasdel)
@@ -4470,8 +4460,25 @@ xfs_bmapi_convert_delalloc(
 	bma.length = max_t(xfs_filblks_t, bma.got.br_blockcount, MAXEXTLEN);
 	bma.total = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
 	bma.minleft = xfs_bmapi_minleft(tp, ip, whichfork);
+
+	/*
+	 * When we're converting the delalloc reservations backing dirty pages
+	 * in the page cache, we must be careful about how we create the new
+	 * extents:
+	 *
+	 * New CoW fork extents are created unwritten, turned into real extents
+	 * when we're about to write the data to disk, and mapped into the data
+	 * fork after the write finishes.  End of story.
+	 *
+	 * New data fork extents below the on-disk EOF must be created
+	 * unwritten and converted to real extents after the write succeeds
+	 * to avoid exposing stale disk contents if we crash.
+	 */
 	if (whichfork == XFS_COW_FORK)
 		bma.flags = XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC;
+	else if (ip->i_d.di_size > 0 &&
+		 bma.offset <= XFS_B_TO_FSBT(mp, ip->i_d.di_size - 1))
+		bma.flags = XFS_BMAPI_PREALLOC;
 
 	if (!xfs_iext_peek_prev_extent(ifp, &bma.icur, &bma.prev))
 		bma.prev.br_startoff = NULLFILEOFF;