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>

2 files changed, 8 insertions, 4 deletions

diff --git a/include/linux/jbd.h b/include/linux/jbd.h
index 9716d370c501..c8f32975f0e4 100644
--- a/include/linux/jbd.h
+++ b/include/linux/jbd.h
@@ -864,7 +864,8 @@ extern int	   journal_destroy    (journal_t *);
 extern int         journal_recover    (journal_t *journal);
 extern int         journal_wipe       (journal_t *, int);
 extern int         journal_skip_recovery        (journal_t *);
-extern void        journal_update_sb_log_tail   (journal_t *);
+extern void        journal_update_sb_log_tail   (journal_t *, tid_t, unsigned int,
+                                                 int);
 extern void        journal_abort      (journal_t *, int);
 extern int         journal_errno      (journal_t *);
 extern void        journal_ack_err    (journal_t *);
diff --git a/include/trace/events/jbd.h b/include/trace/events/jbd.h
index d9658a940a39..da6f2591c25e 100644
--- a/include/trace/events/jbd.h
+++ b/include/trace/events/jbd.h
@@ -170,19 +170,22 @@ TRACE_EVENT(jbd_cleanup_journal_tail,
 );
 
 TRACE_EVENT(journal_write_superblock,
-        TP_PROTO(journal_t *journal),
+        TP_PROTO(journal_t *journal, int write_op),
 
-        TP_ARGS(journal),
+        TP_ARGS(journal, write_op),
 
         TP_STRUCT__entry(
                 __field(        dev_t,  dev                     )
+                __field(        int,    write_op                )
         ),
 
         TP_fast_assign(
                 __entry->dev            = journal->j_fs_dev->bd_dev;
+                __entry->write_op       = write_op;
         ),
 
-        TP_printk("dev %d,%d", MAJOR(__entry->dev), MINOR(__entry->dev))
+        TP_printk("dev %d,%d write_op %x", MAJOR(__entry->dev),
+                  MINOR(__entry->dev), __entry->write_op)
 );
 
 #endif /* _TRACE_JBD_H */