jbd2: issue cache flush after checkpointing even with internal journal

When we reach jbd2_cleanup_journal_tail(), there is no guarantee that
checkpointed buffers are on a stable storage - especially if buffers were
written out by jbd2_log_do_checkpoint(), they are likely to be only in disk's
caches. Thus when we update journal superblock effectively removing old
transaction from journal, this write of superblock can get to stable storage
before those checkpointed buffers which can result in filesystem corruption
after a crash. Thus we must unconditionally issue a cache flush before we
update journal superblock in these cases.

A similar problem can also occur if journal superblock is written only in
disk's caches, other transaction starts reusing space of the transaction
cleaned from the log and power failure happens. 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>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 117 insertions, 21 deletions

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index fc5f2ac..c5ff177 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -742,6 +742,85 @@ struct journal_head *jbd2_journal_get_descriptor_buffer(journal_t *journal)
 	return jbd2_journal_add_journal_head(bh);
 }
 
+/*
+ * Return tid of the oldest transaction in the journal and block in the journal
+ * where the transaction starts.
+ *
+ * If the journal is now empty, return which will be the next transaction ID
+ * we will write and where will that transaction start.
+ *
+ * The return value is 0 if journal tail cannot be pushed any further, 1 if
+ * it can.
+ */
+int jbd2_journal_get_log_tail(journal_t *journal, tid_t *tid,
+			      unsigned long *block)
+{
+	transaction_t *transaction;
+	int ret;
+
+	read_lock(&journal->j_state_lock);
+	spin_lock(&journal->j_list_lock);
+	transaction = journal->j_checkpoint_transactions;
+	if (transaction) {
+		*tid = transaction->t_tid;
+		*block = transaction->t_log_start;
+	} else if ((transaction = journal->j_committing_transaction) != NULL) {
+		*tid = transaction->t_tid;
+		*block = transaction->t_log_start;
+	} else if ((transaction = journal->j_running_transaction) != NULL) {
+		*tid = transaction->t_tid;
+		*block = journal->j_head;
+	} else {
+		*tid = journal->j_transaction_sequence;
+		*block = journal->j_head;
+	}
+	ret = tid_gt(*tid, journal->j_tail_sequence);
+	spin_unlock(&journal->j_list_lock);
+	read_unlock(&journal->j_state_lock);
+
+	return ret;
+}
+
+/*
+ * Update information in journal structure and in on disk journal superblock
+ * about log tail. This function does not check whether information passed in
+ * really pushes log tail further. It's responsibility of the caller to make
+ * sure provided log tail information is valid (e.g. by holding
+ * j_checkpoint_mutex all the time between computing log tail and calling this
+ * function as is the case with jbd2_cleanup_journal_tail()).
+ *
+ * Requires j_checkpoint_mutex
+ */
+void __jbd2_update_log_tail(journal_t *journal, tid_t tid, unsigned long block)
+{
+	unsigned long freed;
+
+	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
+
+	/*
+	 * We cannot afford for write to remain in drive's caches since as
+	 * soon as we update j_tail, next transaction can start reusing journal
+	 * space and if we lose sb update during power failure we'd replay
+	 * old transaction with possibly newly overwritten data.
+	 */
+	jbd2_journal_update_sb_log_tail(journal, tid, block, WRITE_FUA);
+	write_lock(&journal->j_state_lock);
+	freed = block - journal->j_tail;
+	if (block < journal->j_tail)
+		freed += journal->j_last - journal->j_first;
+
+	trace_jbd2_update_log_tail(journal, tid, block, freed);
+	jbd_debug(1,
+		  "Cleaning journal tail from %d to %d (offset %lu), "
+		  "freeing %lu\n",
+		  journal->j_tail_sequence, tid, block, freed);
+
+	journal->j_free += freed;
+	journal->j_tail_sequence = tid;
+	journal->j_tail = block;
+	write_unlock(&journal->j_state_lock);
+}
+
 struct jbd2_stats_proc_session {
 	journal_t *journal;
 	struct transaction_stats_s *stats;
@@ -1125,18 +1204,30 @@ 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. */
-		jbd2_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.
+		 */
+		jbd2_journal_update_sb_log_tail(journal,
+						journal->j_tail_sequence,
+						journal->j_tail,
+						WRITE_FUA);
 		mutex_unlock(&journal->j_checkpoint_mutex);
 	}
 	return jbd2_journal_start_thread(journal);
 }
 
-static void jbd2_write_superblock(journal_t *journal)
+static void jbd2_write_superblock(journal_t *journal, int write_op)
 {
 	struct buffer_head *bh = journal->j_sb_buffer;
+	int ret;
 
-	trace_jbd2_write_superblock(journal);
+	trace_jbd2_write_superblock(journal, write_op);
+	if (!(journal->j_flags & JBD2_BARRIER))
+		write_op &= ~(REQ_FUA | REQ_FLUSH);
+	lock_buffer(bh);
 	if (buffer_write_io_error(bh)) {
 		/*
 		 * Oh, dear.  A previous attempt to write the journal
@@ -1152,40 +1243,45 @@ static void jbd2_write_superblock(journal_t *journal)
 		clear_buffer_write_io_error(bh);
 		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)) {
-		printk(KERN_ERR "JBD2: I/O error detected "
-		       "when updating journal superblock for %s.\n",
-		       journal->j_devname);
 		clear_buffer_write_io_error(bh);
 		set_buffer_uptodate(bh);
+		ret = -EIO;
+	}
+	if (ret) {
+		printk(KERN_ERR "JBD2: Error %d detected when updating "
+		       "journal superblock for %s.\n", ret,
+		       journal->j_devname);
 	}
 }
 
 /**
  * jbd2_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 jbd2_journal_update_sb_log_tail(journal_t *journal)
+void jbd2_journal_update_sb_log_tail(journal_t *journal, tid_t tail_tid,
+				     unsigned long tail_block, int write_op)
 {
 	journal_superblock_t *sb = journal->j_superblock;
 
 	BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
-	read_lock(&journal->j_state_lock);
-	jbd_debug(1, "JBD2: updating superblock (start %ld, seq %d)\n",
-		  journal->j_tail, journal->j_tail_sequence);
+	jbd_debug(1, "JBD2: updating superblock (start %lu, 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);
-	read_unlock(&journal->j_state_lock);
+	sb->s_sequence = cpu_to_be32(tail_tid);
+	sb->s_start    = cpu_to_be32(tail_block);
 
-	jbd2_write_superblock(journal);
+	jbd2_write_superblock(journal, write_op);
 
 	/* Log is no longer empty */
 	write_lock(&journal->j_state_lock);
@@ -1214,7 +1310,7 @@ static void jbd2_mark_journal_empty(journal_t *journal)
 	sb->s_start    = cpu_to_be32(0);
 	read_unlock(&journal->j_state_lock);
 
-	jbd2_write_superblock(journal);
+	jbd2_write_superblock(journal, WRITE_FUA);
 
 	/* Log is no longer empty */
 	write_lock(&journal->j_state_lock);
@@ -1240,7 +1336,7 @@ static void jbd2_journal_update_sb_errno(journal_t *journal)
 	sb->s_errno    = cpu_to_be32(journal->j_errno);
 	read_unlock(&journal->j_state_lock);
 
-	jbd2_write_superblock(journal);
+	jbd2_write_superblock(journal, WRITE_SYNC);
 }
 
 /*