[XFS] get_bulkall() could return incorrect inode state

In the following scenario xfs_bulkstat() returns incorrect stale inode
state:

1. File_A is created and its inode synced to disk. 2. File_A is unlinked
and doesn't exist anymore. 3. Filesystem sync is invoked. 4. File_B is
created. File_B happens to reclaim File_A's inode. 5. xfs_bulkstat() is
called and detects File_B but reports the

incorrect File_A inode state.

Explanation for the incorrect inode state is that inodes are not
immediately synced on file create for performance reasons. This leaves the
on-disk inode buffer uninitialized (or with old state from a previous
generation inode) and this is what xfs_bulkstat() would report.

The patch marks the on-disk inode buffer "dirty" on unlink. When the inode
is reclaimed (by a new file create), xfs_bulkstat() would filter this
inode by the "dirty" mark. Once the inode is flushed to disk, the on-disk
buffer "dirty" mark is automatically removed and a following
xfs_bulkstat() would return the correct inode state.

Marking the on-disk inode buffer "dirty" on unlink is achieved by setting
the on-disk di_nlink field to 0. Note that the in-core di_nlink has
already been set to 0 and a corresponding transaction logged by
xfs_droplink(). This is an exception from the rule that any on-disk inode
buffer changes has to be followed by a disk write (inode flush).
Synchronizing the in-core to on-disk di_nlink values in advance (before
the actual inode flush to disk) should be fine in this case because the
inode is already unlinked and it would never change its di_nlink again for
this inode generation.

SGI-PV: 970842
SGI-Modid: xfs-linux-melb:xfs-kern:29757a

Signed-off-by: Vlad Apostolov <vapo@sgi.com>
Signed-off-by: Alex Elder <aelder@sgi.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Mark Goodwin <markgw@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>

fs/xfs/xfs_inode.c

@@ -1931,9 +1931,9 @@ xfs_iunlink(
 	 */
 	error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp, agdaddr,
 				   XFS_FSS_TO_BB(mp, 1), 0, &agibp);
-	if (error) {
+	if (error)
 		return error;
-	}
+
 	/*
 	 * Validate the magic number of the agi block.
 	 */
@@ -1957,6 +1957,24 @@ xfs_iunlink(
 	ASSERT(agi->agi_unlinked[bucket_index]);
 	ASSERT(be32_to_cpu(agi->agi_unlinked[bucket_index]) != agino);
 
+	error = xfs_itobp(mp, tp, ip, &dip, &ibp, 0, 0);
+	if (error)
+		return error;
+
+	/*
+	 * Clear the on-disk di_nlink. This is to prevent xfs_bulkstat
+	 * from picking up this inode when it is reclaimed (its incore state
+	 * initialzed but not flushed to disk yet). The in-core di_nlink is
+	 * already cleared in xfs_droplink() and a corresponding transaction
+	 * logged. The hack here just synchronizes the in-core to on-disk
+	 * di_nlink value in advance before the actual inode sync to disk.
+	 * This is OK because the inode is already unlinked and would never
+	 * change its di_nlink again for this inode generation.
+	 * This is a temporary hack that would require a proper fix
+	 * in the future.
+	 */
+	dip->di_core.di_nlink = 0;
+
 	if (be32_to_cpu(agi->agi_unlinked[bucket_index]) != NULLAGINO) {
 		/*
 		 * There is already another inode in the bucket we need
@@ -1964,10 +1982,6 @@ xfs_iunlink(
 		 * Here we put the head pointer into our next pointer,
 		 * and then we fall through to point the head at us.
 		 */
-		error = xfs_itobp(mp, tp, ip, &dip, &ibp, 0, 0);
-		if (error) {
-			return error;
-		}
 		ASSERT(be32_to_cpu(dip->di_next_unlinked) == NULLAGINO);
 		/* both on-disk, don't endian flip twice */
 		dip->di_next_unlinked = agi->agi_unlinked[bucket_index];

fs/xfs/xfs_itable.c

@@ -290,8 +290,16 @@ xfs_bulkstat_use_dinode(
 		return 1;
 	dip = (xfs_dinode_t *)
 			xfs_buf_offset(bp, clustidx << mp->m_sb.sb_inodelog);
+	/*
+	 * Check the buffer containing the on-disk inode for di_nlink == 0.
+	 * This is to prevent xfs_bulkstat from picking up just reclaimed
+	 * inodes that have their in-core state initialized but not flushed
+	 * to disk yet. This is a temporary hack that would require a proper
+	 * fix in the future.
+	 */
 	if (be16_to_cpu(dip->di_core.di_magic) != XFS_DINODE_MAGIC ||
-	    !XFS_DINODE_GOOD_VERSION(dip->di_core.di_version))
+	    !XFS_DINODE_GOOD_VERSION(dip->di_core.di_version) ||
+	    !dip->di_core.di_nlink)
 		return 0;
 	if (flags & BULKSTAT_FG_QUICK) {
 		*dipp = dip;