jbd: Write journal superblock with WRITE_FUA after checkpointing

If journal superblock is written only in disk's caches and other transaction
starts reusing space of the transaction cleaned from the log, it can happen
blocks of a new transaction reach the disk before journal superblock. When
power failure happens in such case, subsequent journal replay would still try
to replay the old transaction but some of it's blocks may be already
overwritten by the new transaction. For this reason we must use WRITE_FUA when
updating log tail and we must first write new log tail to disk and update
in-memory information only after that.

Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 39 insertions, 21 deletions

diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index b29c767..425c2f2 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -938,8 +938,16 @@ static int journal_reset(journal_t *journal)
 	} else {
 		/* Lock here to make assertions happy... */
 		mutex_lock(&journal->j_checkpoint_mutex);
-		/* Add the dynamic fields and write it to disk. */
-		journal_update_sb_log_tail(journal);
+		/*
+		 * Update log tail information. We use WRITE_FUA since new
+		 * transaction will start reusing journal space and so we
+		 * must make sure information about current log tail is on
+		 * disk before that.
+		 */
+		journal_update_sb_log_tail(journal,
+					   journal->j_tail_sequence,
+					   journal->j_tail,
+					   WRITE_FUA);
 		mutex_unlock(&journal->j_checkpoint_mutex);
 	}
 	return journal_start_thread(journal);
@@ -1018,11 +1026,15 @@ int journal_create(journal_t *journal)
 	return journal_reset(journal);
 }
 
-static void journal_write_superblock(journal_t *journal)
+static void journal_write_superblock(journal_t *journal, int write_op)
 {
 	struct buffer_head *bh = journal->j_sb_buffer;
+	int ret;
 
-	trace_journal_write_superblock(journal);
+	trace_journal_write_superblock(journal, write_op);
+	if (!(journal->j_flags & JFS_BARRIER))
+		write_op &= ~(REQ_FUA | REQ_FLUSH);
+	lock_buffer(bh);
 	if (buffer_write_io_error(bh)) {
 		char b[BDEVNAME_SIZE];
 		/*
@@ -1040,40 +1052,46 @@ static void journal_write_superblock(journal_t *journal)
 		set_buffer_uptodate(bh);
 	}
 
-	BUFFER_TRACE(bh, "marking dirty");
-	mark_buffer_dirty(bh);
-	sync_dirty_buffer(bh);
+	get_bh(bh);
+	bh->b_end_io = end_buffer_write_sync;
+	ret = submit_bh(write_op, bh);
+	wait_on_buffer(bh);
 	if (buffer_write_io_error(bh)) {
-		char b[BDEVNAME_SIZE];
-		printk(KERN_ERR "JBD: I/O error detected "
-		       "when updating journal superblock for %s.\n",
-		       journal_dev_name(journal, b));
 		clear_buffer_write_io_error(bh);
 		set_buffer_uptodate(bh);
+		ret = -EIO;
+	}
+	if (ret) {
+		char b[BDEVNAME_SIZE];
+		printk(KERN_ERR "JBD: Error %d detected "
+		       "when updating journal superblock for %s.\n",
+		       ret, journal_dev_name(journal, b));
 	}
 }
 
 /**
  * journal_update_sb_log_tail() - Update log tail in journal sb on disk.
  * @journal: The journal to update.
+ * @tail_tid: TID of the new transaction at the tail of the log
+ * @tail_block: The first block of the transaction at the tail of the log
+ * @write_op: With which operation should we write the journal sb
  *
  * Update a journal's superblock information about log tail and write it to
  * disk, waiting for the IO to complete.
  */
-void journal_update_sb_log_tail(journal_t *journal)
+void journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,
+				unsigned int tail_block, int write_op)
 {
 	journal_superblock_t *sb = journal->j_superblock;
 
 	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
-	spin_lock(&journal->j_state_lock);
-	jbd_debug(1,"JBD: updating superblock (start %u, seq %d, errno %d)\n",
-		  journal->j_tail, journal->j_tail_sequence, journal->j_errno);
+	jbd_debug(1,"JBD: updating superblock (start %u, seq %u)\n",
+		  tail_block, tail_tid);
 
-	sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
-	sb->s_start    = cpu_to_be32(journal->j_tail);
-	spin_unlock(&journal->j_state_lock);
+	sb->s_sequence = cpu_to_be32(tail_tid);
+	sb->s_start    = cpu_to_be32(tail_block);
 
-	journal_write_superblock(journal);
+	journal_write_superblock(journal, write_op);
 
 	/* Log is no longer empty */
 	spin_lock(&journal->j_state_lock);
@@ -1102,7 +1120,7 @@ static void mark_journal_empty(journal_t *journal)
 	sb->s_start    = cpu_to_be32(0);
 	spin_unlock(&journal->j_state_lock);
 
-	journal_write_superblock(journal);
+	journal_write_superblock(journal, WRITE_FUA);
 
 	spin_lock(&journal->j_state_lock);
 	/* Log is empty */
@@ -1127,7 +1145,7 @@ static void journal_update_sb_errno(journal_t *journal)
 	sb->s_errno = cpu_to_be32(journal->j_errno);
 	spin_unlock(&journal->j_state_lock);
 
-	journal_write_superblock(journal);
+	journal_write_superblock(journal, WRITE_SYNC);
 }
 
 /*