xfs: rework dquot CRCs

Calculating dquot CRCs when the backing buffer is written back just
doesn't work reliably. There are several places which manipulate
dquots directly in the buffers, and they don't calculate CRCs
appropriately, nor do they always set the buffer up to calculate
CRCs appropriately.

Firstly, if we log a dquot buffer (e.g. during allocation) it gets
logged without valid CRC, and so on recovery we end up with a dquot
that is not valid.

Secondly, if we recover/repair a dquot, we don't have a verifier
attached to the buffer and hence CRCs are not calculated on the way
down to disk.

Thirdly, calculating the CRC after we've changed the contents means
that if we re-read the dquot from the buffer, we cannot verify the
contents of the dquot are valid, as the CRC is invalid.

So, to avoid all the dquot CRC errors that are being detected by the
read verifier, change to using the same model as for inodes. That
is, dquot CRCs are calculated and written to the backing buffer at
the time the dquot is flushed to the backing buffer. If we modify
the dquot directly in the backing buffer, calculate the CRC
immediately after the modification is complete. Hence the dquot in
the on-disk buffer should always have a valid CRC.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 16 insertions, 21 deletions

diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
index a41f8bf..044e97a 100644
--- a/fs/xfs/xfs_dquot.c
+++ b/fs/xfs/xfs_dquot.c
@@ -249,8 +249,11 @@ xfs_qm_init_dquot_blk(
 		d->dd_diskdq.d_version = XFS_DQUOT_VERSION;
 		d->dd_diskdq.d_id = cpu_to_be32(curid);
 		d->dd_diskdq.d_flags = type;
-		if (xfs_sb_version_hascrc(&mp->m_sb))
+		if (xfs_sb_version_hascrc(&mp->m_sb)) {
 			uuid_copy(&d->dd_uuid, &mp->m_sb.sb_uuid);
+			xfs_update_cksum((char *)d, sizeof(struct xfs_dqblk),
+					 XFS_DQUOT_CRC_OFF);
+		}
 	}
 
 	xfs_trans_dquot_buf(tp, bp,
@@ -286,23 +289,6 @@ xfs_dquot_set_prealloc_limits(struct xfs_dquot *dqp)
 	dqp->q_low_space[XFS_QLOWSP_5_PCNT] = space * 5;
 }
 
-STATIC void
-xfs_dquot_buf_calc_crc(
-	struct xfs_mount	*mp,
-	struct xfs_buf		*bp)
-{
-	struct xfs_dqblk	*d = (struct xfs_dqblk *)bp->b_addr;
-	int			i;
-
-	if (!xfs_sb_version_hascrc(&mp->m_sb))
-		return;
-
-	for (i = 0; i < mp->m_quotainfo->qi_dqperchunk; i++, d++) {
-		xfs_update_cksum((char *)d, sizeof(struct xfs_dqblk),
-				 offsetof(struct xfs_dqblk, dd_crc));
-	}
-}
-
 STATIC bool
 xfs_dquot_buf_verify_crc(
 	struct xfs_mount	*mp,
@@ -328,12 +314,11 @@ xfs_dquot_buf_verify_crc(
 
 	for (i = 0; i < ndquots; i++, d++) {
 		if (!xfs_verify_cksum((char *)d, sizeof(struct xfs_dqblk),
-				 offsetof(struct xfs_dqblk, dd_crc)))
+				 XFS_DQUOT_CRC_OFF))
 			return false;
 		if (!uuid_equal(&d->dd_uuid, &mp->m_sb.sb_uuid))
 			return false;
 	}
-
 	return true;
 }
 
@@ -393,6 +378,11 @@ xfs_dquot_buf_read_verify(
 	}
 }
 
+/*
+ * we don't calculate the CRC here as that is done when the dquot is flushed to
+ * the buffer after the update is done. This ensures that the dquot in the
+ * buffer always has an up-to-date CRC value.
+ */
 void
 xfs_dquot_buf_write_verify(
 	struct xfs_buf	*bp)
@@ -404,7 +394,6 @@ xfs_dquot_buf_write_verify(
 		xfs_buf_ioerror(bp, EFSCORRUPTED);
 		return;
 	}
-	xfs_dquot_buf_calc_crc(mp, bp);
 }
 
 const struct xfs_buf_ops xfs_dquot_buf_ops = {
@@ -1151,11 +1140,17 @@ xfs_qm_dqflush(
 	 * copy the lsn into the on-disk dquot now while we have the in memory
 	 * dquot here. This can't be done later in the write verifier as we
 	 * can't get access to the log item at that point in time.
+	 *
+	 * We also calculate the CRC here so that the on-disk dquot in the
+	 * buffer always has a valid CRC. This ensures there is no possibility
+	 * of a dquot without an up-to-date CRC getting to disk.
 	 */
 	if (xfs_sb_version_hascrc(&mp->m_sb)) {
 		struct xfs_dqblk *dqb = (struct xfs_dqblk *)ddqp;
 
 		dqb->dd_lsn = cpu_to_be64(dqp->q_logitem.qli_item.li_lsn);
+		xfs_update_cksum((char *)dqb, sizeof(struct xfs_dqblk),
+				 XFS_DQUOT_CRC_OFF);
 	}
 
 	/*