xfs: add CRC checks to the log

Implement CRCs for the log buffers.  We re-use a field in
struct xlog_rec_header that was used for a weak checksum of the
log buffer payload in debug builds before.

The new checksumming uses the crc32c checksum we will use elsewhere
in XFS, and also protects the record header and addition cycle data.

Due to this there are some interesting changes in xlog_sync, as we
need to do the cycle wrapping for the split buffer case much earlier,
as we would touch the buffer after generating the checksum otherwise.

The CRC calculation is always enabled, even for non-CRC filesystems,
as adding this CRC does not change the log format. On non-CRC
filesystems, only issue an alert if a CRC mismatch is found and
allow recovery to continue - this will act as an indicator that
log recovery problems are a result of log corruption. On CRC enabled
filesystems, however, log recovery will fail.

Note that existing debug kernels will write a simple checksum value
to the log, so the first time this is run on a filesystem taht was
last used on a debug kernel it will through CRC mismatch warning
errors. These can be ignored.

Initially based on a patch from Dave Chinner, then modified
significantly by Christoph Hellwig.  Modified again by Dave Chinner
to get to this version.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

1 files changed, 63 insertions, 69 deletions

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 931e8e23f192..9c3651c9e75b 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 @@ xlog_recover_process_iunlinks(
 	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;
-
-	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;
+	__be32			crc;
+
+	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 @@ xlog_unpack_data(
 			dp += BBSIZE;
 		}
 	}
+
+	return 0;
 }
 
 STATIC int
@@ -3437,9 +3418,13 @@ xlog_do_recovery_pass(
 			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 @@ xlog_do_recovery_pass(
 				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 @@ xlog_do_recovery_pass(
 			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;
 		}