diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 1d6d2ee..c6d6e13 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -35,6 +35,7 @@
 #include "xfs_inode.h"
 #include "xfs_trace.h"
 #include "xfs_fsops.h"
+#include "xfs_cksum.h"
 
 kmem_zone_t	*xfs_log_ticket_zone;
 
@@ -1490,6 +1491,84 @@
 }
 
 /*
+ * Stamp cycle number in every block
+ */
+STATIC void
+xlog_pack_data(
+	struct xlog		*log,
+	struct xlog_in_core	*iclog,
+	int			roundoff)
+{
+	int			i, j, k;
+	int			size = iclog->ic_offset + roundoff;
+	__be32			cycle_lsn;
+	xfs_caddr_t		dp;
+
+	cycle_lsn = CYCLE_LSN_DISK(iclog->ic_header.h_lsn);
+
+	dp = iclog->ic_datap;
+	for (i = 0; i < BTOBB(size); i++) {
+		if (i >= (XLOG_HEADER_CYCLE_SIZE / BBSIZE))
+			break;
+		iclog->ic_header.h_cycle_data[i] = *(__be32 *)dp;
+		*(__be32 *)dp = cycle_lsn;
+		dp += BBSIZE;
+	}
+
+	if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
+		xlog_in_core_2_t *xhdr = iclog->ic_data;
+
+		for ( ; i < BTOBB(size); i++) {
+			j = i / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
+			k = i % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
+			xhdr[j].hic_xheader.xh_cycle_data[k] = *(__be32 *)dp;
+			*(__be32 *)dp = cycle_lsn;
+			dp += BBSIZE;
+		}
+
+		for (i = 1; i < log->l_iclog_heads; i++)
+			xhdr[i].hic_xheader.xh_cycle = cycle_lsn;
+	}
+}
+
+/*
+ * Calculate the checksum for a log buffer.
+ *
+ * This is a little more complicated than it should be because the various
+ * headers and the actual data are non-contiguous.
+ */
+__be32
+xlog_cksum(
+	struct xlog		*log,
+	struct xlog_rec_header	*rhead,
+	char			*dp,
+	int			size)
+{
+	__uint32_t		crc;
+
+	/* first generate the crc for the record header ... */
+	crc = xfs_start_cksum((char *)rhead,
+			      sizeof(struct xlog_rec_header),
+			      offsetof(struct xlog_rec_header, h_crc));
+
+	/* ... then for additional cycle data for v2 logs ... */
+	if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
+		union xlog_in_core2 *xhdr = (union xlog_in_core2 *)rhead;
+		int		i;
+
+		for (i = 1; i < log->l_iclog_heads; i++) {
+			crc = crc32c(crc, &xhdr[i].hic_xheader,
+				     sizeof(struct xlog_rec_ext_header));
+		}
+	}
+
+	/* ... and finally for the payload */
+	crc = crc32c(crc, dp, size);
+
+	return xfs_end_cksum(crc);
+}
+
+/*
  * The bdstrat callback function for log bufs. This gives us a central
  * place to trap bufs in case we get hit by a log I/O error and need to
  * shutdown. Actually, in practice, even when we didn't get a log error,
@@ -1549,7 +1628,6 @@
 	struct xlog		*log,
 	struct xlog_in_core	*iclog)
 {
-	xfs_caddr_t	dptr;		/* pointer to byte sized element */
 	xfs_buf_t	*bp;
 	int		i;
 	uint		count;		/* byte count of bwrite */
@@ -1558,6 +1636,7 @@
 	int		split = 0;	/* split write into two regions */
 	int		error;
 	int		v2 = xfs_sb_version_haslogv2(&log->l_mp->m_sb);
+	int		size;
 
 	XFS_STATS_INC(xs_log_writes);
 	ASSERT(atomic_read(&iclog->ic_refcnt) == 0);
@@ -1588,13 +1667,10 @@
 	xlog_pack_data(log, iclog, roundoff); 
 
 	/* real byte length */
-	if (v2) {
-		iclog->ic_header.h_len =
-			cpu_to_be32(iclog->ic_offset + roundoff);
-	} else {
-		iclog->ic_header.h_len =
-			cpu_to_be32(iclog->ic_offset);
-	}
+	size = iclog->ic_offset;
+	if (v2)
+		size += roundoff;
+	iclog->ic_header.h_len = cpu_to_be32(size);
 
 	bp = iclog->ic_bp;
 	XFS_BUF_SET_ADDR(bp, BLOCK_LSN(be64_to_cpu(iclog->ic_header.h_lsn)));
@@ -1603,12 +1679,36 @@
 
 	/* Do we need to split this write into 2 parts? */
 	if (XFS_BUF_ADDR(bp) + BTOBB(count) > log->l_logBBsize) {
+		char		*dptr;
+
 		split = count - (BBTOB(log->l_logBBsize - XFS_BUF_ADDR(bp)));
 		count = BBTOB(log->l_logBBsize - XFS_BUF_ADDR(bp));
-		iclog->ic_bwritecnt = 2;	/* split into 2 writes */
+		iclog->ic_bwritecnt = 2;
+
+		/*
+		 * Bump the cycle numbers at the start of each block in the
+		 * part of the iclog that ends up in the buffer that gets
+		 * written to the start of the log.
+		 *
+		 * Watch out for the header magic number case, though.
+		 */
+		dptr = (char *)&iclog->ic_header + count;
+		for (i = 0; i < split; i += BBSIZE) {
+			__uint32_t cycle = be32_to_cpu(*(__be32 *)dptr);
+			if (++cycle == XLOG_HEADER_MAGIC_NUM)
+				cycle++;
+			*(__be32 *)dptr = cpu_to_be32(cycle);
+
+			dptr += BBSIZE;
+		}
 	} else {
 		iclog->ic_bwritecnt = 1;
 	}
+
+	/* calculcate the checksum */
+	iclog->ic_header.h_crc = xlog_cksum(log, &iclog->ic_header,
+					    iclog->ic_datap, size);
+
 	bp->b_io_length = BTOBB(count);
 	bp->b_fspriv = iclog;
 	XFS_BUF_ZEROFLAGS(bp);
@@ -1662,19 +1762,6 @@
 		bp->b_flags |= XBF_SYNCIO;
 		if (log->l_mp->m_flags & XFS_MOUNT_BARRIER)
 			bp->b_flags |= XBF_FUA;
-		dptr = bp->b_addr;
-		/*
-		 * Bump the cycle numbers at the start of each block
-		 * since this part of the buffer is at the start of
-		 * a new cycle.  Watch out for the header magic number
-		 * case, though.
-		 */
-		for (i = 0; i < split; i += BBSIZE) {
-			be32_add_cpu((__be32 *)dptr, 1);
-			if (be32_to_cpu(*(__be32 *)dptr) == XLOG_HEADER_MAGIC_NUM)
-				be32_add_cpu((__be32 *)dptr, 1);
-			dptr += BBSIZE;
-		}
 
 		ASSERT(XFS_BUF_ADDR(bp) <= log->l_logBBsize-1);
 		ASSERT(XFS_BUF_ADDR(bp) + BTOBB(count) <= log->l_logBBsize);
@@ -1691,7 +1778,6 @@
 	return 0;
 }	/* xlog_sync */
 
-
 /*
  * Deallocate a log structure
  */
diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
index 9a4e0e5..dc3498b 100644
--- a/fs/xfs/xfs_log_priv.h
+++ b/fs/xfs/xfs_log_priv.h
@@ -139,7 +139,6 @@
 /*
  * Flags for log structure
  */
-#define XLOG_CHKSUM_MISMATCH	0x1	/* used only during recovery */
 #define XLOG_ACTIVE_RECOVERY	0x2	/* in the middle of recovery */
 #define	XLOG_RECOVERY_NEEDED	0x4	/* log was recovered */
 #define XLOG_IO_ERROR		0x8	/* log hit an I/O error, and being
@@ -291,7 +290,7 @@
 	__be32	  h_len;	/* len in bytes; should be 64-bit aligned: 4 */
 	__be64	  h_lsn;	/* lsn of this LR			:  8 */
 	__be64	  h_tail_lsn;	/* lsn of 1st LR w/ buffers not committed: 8 */
-	__be32	  h_chksum;	/* may not be used; non-zero if used	:  4 */
+	__le32	  h_crc;	/* crc of log record                    :  4 */
 	__be32	  h_prev_block; /* block number to previous LR		:  4 */
 	__be32	  h_num_logops;	/* number of log operations in this LR	:  4 */
 	__be32	  h_cycle_data[XLOG_HEADER_CYCLE_SIZE / BBSIZE];
@@ -555,11 +554,9 @@
 extern int
 xlog_recover_finish(
 	struct xlog		*log);
-extern void
-xlog_pack_data(
-	struct xlog		*log,
-	struct xlog_in_core	*iclog,
-	int);
+
+extern __be32	 xlog_cksum(struct xlog *log, struct xlog_rec_header *rhead,
+			    char *dp, int size);
 
 extern kmem_zone_t *xfs_log_ticket_zone;
 struct xlog_ticket *
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 931e8e2..9c3651c 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -41,6 +41,7 @@
 #include "xfs_trans_priv.h"
 #include "xfs_quota.h"
 #include "xfs_utils.h"
+#include "xfs_cksum.h"
 #include "xfs_trace.h"
 #include "xfs_icache.h"
 
@@ -3216,80 +3217,58 @@
 	mp->m_dmevmask = mp_dmevmask;
 }
 
-
-#ifdef DEBUG
-STATIC void
-xlog_pack_data_checksum(
-	struct xlog		*log,
-	struct xlog_in_core	*iclog,
-	int			size)
-{
-	int		i;
-	__be32		*up;
-	uint		chksum = 0;
-
-	up = (__be32 *)iclog->ic_datap;
-	/* divide length by 4 to get # words */
-	for (i = 0; i < (size >> 2); i++) {
-		chksum ^= be32_to_cpu(*up);
-		up++;
-	}
-	iclog->ic_header.h_chksum = cpu_to_be32(chksum);
-}
-#else
-#define xlog_pack_data_checksum(log, iclog, size)
-#endif
-
 /*
- * Stamp cycle number in every block
+ * Upack the log buffer data and crc check it. If the check fails, issue a
+ * warning if and only if the CRC in the header is non-zero. This makes the
+ * check an advisory warning, and the zero CRC check will prevent failure
+ * warnings from being emitted when upgrading the kernel from one that does not
+ * add CRCs by default.
+ *
+ * When filesystems are CRC enabled, this CRC mismatch becomes a fatal log
+ * corruption failure
  */
-void
-xlog_pack_data(
-	struct xlog		*log,
-	struct xlog_in_core	*iclog,
-	int			roundoff)
+STATIC int
+xlog_unpack_data_crc(
+	struct xlog_rec_header	*rhead,
+	xfs_caddr_t		dp,
+	struct xlog		*log)
 {
-	int			i, j, k;
-	int			size = iclog->ic_offset + roundoff;
-	__be32			cycle_lsn;
-	xfs_caddr_t		dp;
+	__be32			crc;
 
-	xlog_pack_data_checksum(log, iclog, size);
-
-	cycle_lsn = CYCLE_LSN_DISK(iclog->ic_header.h_lsn);
-
-	dp = iclog->ic_datap;
-	for (i = 0; i < BTOBB(size) &&
-		i < (XLOG_HEADER_CYCLE_SIZE / BBSIZE); i++) {
-		iclog->ic_header.h_cycle_data[i] = *(__be32 *)dp;
-		*(__be32 *)dp = cycle_lsn;
-		dp += BBSIZE;
-	}
-
-	if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
-		xlog_in_core_2_t *xhdr = iclog->ic_data;
-
-		for ( ; i < BTOBB(size); i++) {
-			j = i / (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
-			k = i % (XLOG_HEADER_CYCLE_SIZE / BBSIZE);
-			xhdr[j].hic_xheader.xh_cycle_data[k] = *(__be32 *)dp;
-			*(__be32 *)dp = cycle_lsn;
-			dp += BBSIZE;
+	crc = xlog_cksum(log, rhead, dp, be32_to_cpu(rhead->h_len));
+	if (crc != rhead->h_crc) {
+		if (rhead->h_crc || xfs_sb_version_hascrc(&log->l_mp->m_sb)) {
+			xfs_alert(log->l_mp,
+		"log record CRC mismatch: found 0x%x, expected 0x%x.\n",
+					be32_to_cpu(rhead->h_crc),
+					be32_to_cpu(crc));
+			xfs_hex_dump(dp, 32);
 		}
 
-		for (i = 1; i < log->l_iclog_heads; i++) {
-			xhdr[i].hic_xheader.xh_cycle = cycle_lsn;
-		}
+		/*
+		 * If we've detected a log record corruption, then we can't
+		 * recover past this point. Abort recovery if we are enforcing
+		 * CRC protection by punting an error back up the stack.
+		 */
+		if (xfs_sb_version_hascrc(&log->l_mp->m_sb))
+			return EFSCORRUPTED;
 	}
+
+	return 0;
 }
 
-STATIC void
+STATIC int
 xlog_unpack_data(
 	struct xlog_rec_header	*rhead,
 	xfs_caddr_t		dp,
 	struct xlog		*log)
 {
 	int			i, j, k;
+	int			error;
+
+	error = xlog_unpack_data_crc(rhead, dp, log);
+	if (error)
+		return error;
 
 	for (i = 0; i < BTOBB(be32_to_cpu(rhead->h_len)) &&
 		  i < (XLOG_HEADER_CYCLE_SIZE / BBSIZE); i++) {
@@ -3306,6 +3285,8 @@
 			dp += BBSIZE;
 		}
 	}
+
+	return 0;
 }
 
 STATIC int
@@ -3437,9 +3418,13 @@
 			if (error)
 				goto bread_err2;
 
-			xlog_unpack_data(rhead, offset, log);
-			if ((error = xlog_recover_process_data(log,
-						rhash, rhead, offset, pass)))
+			error = xlog_unpack_data(rhead, offset, log);
+			if (error)
+				goto bread_err2;
+
+			error = xlog_recover_process_data(log,
+						rhash, rhead, offset, pass);
+			if (error)
 				goto bread_err2;
 			blk_no += bblks + hblks;
 		}
@@ -3549,9 +3534,14 @@
 				if (error)
 					goto bread_err2;
 			}
-			xlog_unpack_data(rhead, offset, log);
-			if ((error = xlog_recover_process_data(log, rhash,
-							rhead, offset, pass)))
+
+			error = xlog_unpack_data(rhead, offset, log);
+			if (error)
+				goto bread_err2;
+
+			error = xlog_recover_process_data(log, rhash,
+							rhead, offset, pass);
+			if (error)
 				goto bread_err2;
 			blk_no += bblks;
 		}
@@ -3576,9 +3566,13 @@
 			if (error)
 				goto bread_err2;
 
-			xlog_unpack_data(rhead, offset, log);
-			if ((error = xlog_recover_process_data(log, rhash,
-							rhead, offset, pass)))
+			error = xlog_unpack_data(rhead, offset, log);
+			if (error)
+				goto bread_err2;
+
+			error = xlog_recover_process_data(log, rhash,
+							rhead, offset, pass);
+			if (error)
 				goto bread_err2;
 			blk_no += bblks + hblks;
 		}