[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>

1 files changed, 20 insertions, 6 deletions

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 3d8ba8fec191..abf509a88915 100644
--- a/fs/xfs/xfs_inode.c
+++ b/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];