1 files changed, 289 insertions, 20 deletions

diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 423c36dbcdea..26e67b4450cc 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -61,6 +61,9 @@ xlog_recover_check_summary(
 #else
 #define	xlog_recover_check_summary(log)
 #endif
+STATIC int
+xlog_do_recovery_pass(
+        struct xlog *, xfs_daddr_t, xfs_daddr_t, int, xfs_daddr_t *);
 
 /*
  * This structure is used during recovery to record the buf log items which
@@ -941,6 +944,278 @@ out_error:
 }
 
 /*
+ * Seek forward in the log for log record headers.
+ *
+ * Given head and tail blocks, walk forward from the tail block until we find
+ * the provided number of records or hit the head block. The return value is the
+ * number of records encountered or a negative error code. The log block and
+ * buffer pointer of the last record seen are returned in rblk and rhead
+ * respectively.
+ */
+STATIC int
+xlog_seek_logrec_hdr(
+	struct xlog		*log,
+	xfs_daddr_t		head_blk,
+	xfs_daddr_t		tail_blk,
+	int			count,
+	struct xfs_buf		*bp,
+	xfs_daddr_t		*rblk,
+	struct xlog_rec_header	**rhead,
+	bool			*wrapped)
+{
+	int			i;
+	int			error;
+	int			found = 0;
+	char			*offset = NULL;
+	xfs_daddr_t		end_blk;
+
+	*wrapped = false;
+
+	/*
+	 * Walk forward from the tail block until we hit the head or the last
+	 * block in the log.
+	 */
+	end_blk = head_blk > tail_blk ? head_blk : log->l_logBBsize - 1;
+	for (i = (int) tail_blk; i <= end_blk; i++) {
+		error = xlog_bread(log, i, 1, bp, &offset);
+		if (error)
+			goto out_error;
+
+		if (*(__be32 *) offset == cpu_to_be32(XLOG_HEADER_MAGIC_NUM)) {
+			*rblk = i;
+			*rhead = (struct xlog_rec_header *) offset;
+			if (++found == count)
+				break;
+		}
+	}
+
+	/*
+	 * If we haven't hit the head block or the log record header count,
+	 * start looking again from the start of the physical log.
+	 */
+	if (tail_blk > head_blk && found != count) {
+		for (i = 0; i < (int) head_blk; i++) {
+			error = xlog_bread(log, i, 1, bp, &offset);
+			if (error)
+				goto out_error;
+
+			if (*(__be32 *)offset ==
+			    cpu_to_be32(XLOG_HEADER_MAGIC_NUM)) {
+				*wrapped = true;
+				*rblk = i;
+				*rhead = (struct xlog_rec_header *) offset;
+				if (++found == count)
+					break;
+			}
+		}
+	}
+
+	return found;
+
+out_error:
+	return error;
+}
+
+/*
+ * Check the log tail for torn writes. This is required when torn writes are
+ * detected at the head and the head had to be walked back to a previous record.
+ * The tail of the previous record must now be verified to ensure the torn
+ * writes didn't corrupt the previous tail.
+ *
+ * Return an error if CRC verification fails as recovery cannot proceed.
+ */
+STATIC int
+xlog_verify_tail(
+	struct xlog		*log,
+	xfs_daddr_t		head_blk,
+	xfs_daddr_t		tail_blk)
+{
+	struct xlog_rec_header	*thead;
+	struct xfs_buf		*bp;
+	xfs_daddr_t		first_bad;
+	int			count;
+	int			error = 0;
+	bool			wrapped;
+	xfs_daddr_t		tmp_head;
+
+	bp = xlog_get_bp(log, 1);
+	if (!bp)
+		return -ENOMEM;
+
+	/*
+	 * Seek XLOG_MAX_ICLOGS + 1 records past the current tail record to get
+	 * a temporary head block that points after the last possible
+	 * concurrently written record of the tail.
+	 */
+	count = xlog_seek_logrec_hdr(log, head_blk, tail_blk,
+				     XLOG_MAX_ICLOGS + 1, bp, &tmp_head, &thead,
+				     &wrapped);
+	if (count < 0) {
+		error = count;
+		goto out;
+	}
+
+	/*
+	 * If the call above didn't find XLOG_MAX_ICLOGS + 1 records, we ran
+	 * into the actual log head. tmp_head points to the start of the record
+	 * so update it to the actual head block.
+	 */
+	if (count < XLOG_MAX_ICLOGS + 1)
+		tmp_head = head_blk;
+
+	/*
+	 * We now have a tail and temporary head block that covers at least
+	 * XLOG_MAX_ICLOGS records from the tail. We need to verify that these
+	 * records were completely written. Run a CRC verification pass from
+	 * tail to head and return the result.
+	 */
+	error = xlog_do_recovery_pass(log, tmp_head, tail_blk,
+				      XLOG_RECOVER_CRCPASS, &first_bad);
+
+out:
+	xlog_put_bp(bp);
+	return error;
+}
+
+/*
+ * Detect and trim torn writes from the head of the log.
+ *
+ * Storage without sector atomicity guarantees can result in torn writes in the
+ * log in the event of a crash. Our only means to detect this scenario is via
+ * CRC verification. While we can't always be certain that CRC verification
+ * failure is due to a torn write vs. an unrelated corruption, we do know that
+ * only a certain number (XLOG_MAX_ICLOGS) of log records can be written out at
+ * one time. Therefore, CRC verify up to XLOG_MAX_ICLOGS records at the head of
+ * the log and treat failures in this range as torn writes as a matter of
+ * policy. In the event of CRC failure, the head is walked back to the last good
+ * record in the log and the tail is updated from that record and verified.
+ */
+STATIC int
+xlog_verify_head(
+	struct xlog		*log,
+	xfs_daddr_t		*head_blk,	/* in/out: unverified head */
+	xfs_daddr_t		*tail_blk,	/* out: tail block */
+	struct xfs_buf		*bp,
+	xfs_daddr_t		*rhead_blk,	/* start blk of last record */
+	struct xlog_rec_header	**rhead,	/* ptr to last record */
+	bool			*wrapped)	/* last rec. wraps phys. log */
+{
+	struct xlog_rec_header	*tmp_rhead;
+	struct xfs_buf		*tmp_bp;
+	xfs_daddr_t		first_bad;
+	xfs_daddr_t		tmp_rhead_blk;
+	int			found;
+	int			error;
+	bool			tmp_wrapped;
+
+	/*
+	 * Search backwards through the log looking for the log record header
+	 * block. This wraps all the way back around to the head so something is
+	 * seriously wrong if we can't find it.
+	 */
+	found = xlog_rseek_logrec_hdr(log, *head_blk, *head_blk, 1, bp, rhead_blk,
+				      rhead, wrapped);
+	if (found < 0)
+		return found;
+	if (!found) {
+		xfs_warn(log->l_mp, "%s: couldn't find sync record", __func__);
+		return -EIO;
+	}
+
+	*tail_blk = BLOCK_LSN(be64_to_cpu((*rhead)->h_tail_lsn));
+
+	/*
+	 * Now that we have a tail block, check the head of the log for torn
+	 * writes. Search again until we hit the tail or the maximum number of
+	 * log record I/Os that could have been in flight at one time. Use a
+	 * temporary buffer so we don't trash the rhead/bp pointer from the
+	 * call above.
+	 */
+	tmp_bp = xlog_get_bp(log, 1);
+	if (!tmp_bp)
+		return -ENOMEM;
+	error = xlog_rseek_logrec_hdr(log, *head_blk, *tail_blk,
+				      XLOG_MAX_ICLOGS, tmp_bp, &tmp_rhead_blk,
+				      &tmp_rhead, &tmp_wrapped);
+	xlog_put_bp(tmp_bp);
+	if (error < 0)
+		return error;
+
+	/*
+	 * Now run a CRC verification pass over the records starting at the
+	 * block found above to the current head. If a CRC failure occurs, the
+	 * log block of the first bad record is saved in first_bad.
+	 */
+	error = xlog_do_recovery_pass(log, *head_blk, tmp_rhead_blk,
+				      XLOG_RECOVER_CRCPASS, &first_bad);
+	if (error == -EFSBADCRC) {
+		/*
+		 * We've hit a potential torn write. Reset the error and warn
+		 * about it.
+		 */
+		error = 0;
+		xfs_warn(log->l_mp,
+"Torn write (CRC failure) detected at log block 0x%llx. Truncating head block from 0x%llx.",
+			 first_bad, *head_blk);
+
+		/*
+		 * Get the header block and buffer pointer for the last good
+		 * record before the bad record.
+		 *
+		 * Note that xlog_find_tail() clears the blocks at the new head
+		 * (i.e., the records with invalid CRC) if the cycle number
+		 * matches the the current cycle.
+		 */
+		found = xlog_rseek_logrec_hdr(log, first_bad, *tail_blk, 1, bp,
+					      rhead_blk, rhead, wrapped);
+		if (found < 0)
+			return found;
+		if (found == 0)		/* XXX: right thing to do here? */
+			return -EIO;
+
+		/*
+		 * Reset the head block to the starting block of the first bad
+		 * log record and set the tail block based on the last good
+		 * record.
+		 *
+		 * Bail out if the updated head/tail match as this indicates
+		 * possible corruption outside of the acceptable
+		 * (XLOG_MAX_ICLOGS) range. This is a job for xfs_repair...
+		 */
+		*head_blk = first_bad;
+		*tail_blk = BLOCK_LSN(be64_to_cpu((*rhead)->h_tail_lsn));
+		if (*head_blk == *tail_blk) {
+			ASSERT(0);
+			return 0;
+		}
+
+		/*
+		 * Now verify the tail based on the updated head. This is
+		 * required because the torn writes trimmed from the head could
+		 * have been written over the tail of a previous record. Return
+		 * any errors since recovery cannot proceed if the tail is
+		 * corrupt.
+		 *
+		 * XXX: This leaves a gap in truly robust protection from torn
+		 * writes in the log. If the head is behind the tail, the tail
+		 * pushes forward to create some space and then a crash occurs
+		 * causing the writes into the previous record's tail region to
+		 * tear, log recovery isn't able to recover.
+		 *
+		 * How likely is this to occur? If possible, can we do something
+		 * more intelligent here? Is it safe to push the tail forward if
+		 * we can determine that the tail is within the range of the
+		 * torn write (e.g., the kernel can only overwrite the tail if
+		 * it has actually been pushed forward)? Alternatively, could we
+		 * somehow prevent this condition at runtime?
+		 */
+		error = xlog_verify_tail(log, *head_blk, *tail_blk);
+	}
+
+	return error;
+}
+
+/*
  * Find the sync block number or the tail of the log.
  *
  * This will be the block number of the last record to have its
@@ -966,9 +1241,10 @@ xlog_find_tail(
 	xlog_op_header_t	*op_head;
 	char			*offset = NULL;
 	xfs_buf_t		*bp;
-	int			error, i, found;
+	int			error;
 	xfs_daddr_t		umount_data_blk;
 	xfs_daddr_t		after_umount_blk;
+	xfs_daddr_t		rhead_blk;
 	xfs_lsn_t		tail_lsn;
 	int			hblks;
 	bool			wrapped = false;
@@ -995,24 +1271,16 @@ xlog_find_tail(
 	}
 
 	/*
-	 * Search backwards through the log looking for the log record header
-	 * block. This wraps all the way back around to the head so something is
-	 * seriously wrong if we can't find it.
+	 * Trim the head block back to skip over torn records. We can have
+	 * multiple log I/Os in flight at any time, so we assume CRC failures
+	 * back through the previous several records are torn writes and skip
+	 * them.
 	 */
 	ASSERT(*head_blk < INT_MAX);
-	found = xlog_rseek_logrec_hdr(log, *head_blk, *head_blk, 1, bp, &i,
-				      &rhead, &wrapped);
-	if (found < 0) {
-		error = found;
+	error = xlog_verify_head(log, head_blk, tail_blk, bp, &rhead_blk,
+				 &rhead, &wrapped);
+	if (error)
 		goto done;
-	}
-	if (!found) {
-		xfs_warn(log->l_mp, "%s: couldn't find sync record", __func__);
-		xlog_put_bp(bp);
-		ASSERT(0);
-		return -EIO;
-	}
-	*tail_blk = BLOCK_LSN(be64_to_cpu(rhead->h_tail_lsn));
 
 	/*
 	 * Reset log values according to the state of the log when we
@@ -1024,7 +1292,7 @@ xlog_find_tail(
 	 * written was complete and ended exactly on the end boundary
 	 * of the physical log.
 	 */
-	log->l_prev_block = i;
+	log->l_prev_block = rhead_blk;
 	log->l_curr_block = (int)*head_blk;
 	log->l_curr_cycle = be32_to_cpu(rhead->h_cycle);
 	if (wrapped)
@@ -1062,12 +1330,13 @@ xlog_find_tail(
 	} else {
 		hblks = 1;
 	}
-	after_umount_blk = (i + hblks + (int)
-		BTOBB(be32_to_cpu(rhead->h_len))) % log->l_logBBsize;
+	after_umount_blk = rhead_blk + hblks + BTOBB(be32_to_cpu(rhead->h_len));
+	after_umount_blk = do_mod(after_umount_blk, log->l_logBBsize);
 	tail_lsn = atomic64_read(&log->l_tail_lsn);
 	if (*head_blk == after_umount_blk &&
 	    be32_to_cpu(rhead->h_num_logops) == 1) {
-		umount_data_blk = (i + hblks) % log->l_logBBsize;
+		umount_data_blk = rhead_blk + hblks;
+		umount_data_blk = do_mod(umount_data_blk, log->l_logBBsize);
 		error = xlog_bread(log, umount_data_blk, 1, bp, &offset);
 		if (error)
 			goto done;