ext4: Fix and simplify s_dirt handling

The s_dirt flag wasn't completely handled correctly, but it didn't
really matter when journalling was enabled.  It turns out that when
ext4 runs without a journal, we don't clear s_dirt in places where we
should have, with the result that the high-level write_super()
function was writing the superblock when it wasn't necessary.

So we fix this by making ext4_commit_super() clear the s_dirt flag,
and removing many of the other places where s_dirt is manipulated.
When journalling is enabled, the s_dirt flag might be left set more
often, but s_dirt really doesn't matter when journalling is enabled.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 3 insertions, 11 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index ad4c9be4abdc..7c7a08af1200 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3128,7 +3128,6 @@ static int ext4_load_journal(struct super_block *sb,
         if (journal_devnum &&
             journal_devnum != le32_to_cpu(es->s_journal_dev)) {
                 es->s_journal_dev = cpu_to_le32(journal_devnum);
-                sb->s_dirt = 1;
 
                 /* Make sure we flush the recovery flag to disk. */
                 ext4_commit_super(sb, 1);
@@ -3168,7 +3167,7 @@ static int ext4_commit_super(struct super_block *sb, int sync)
                                         &EXT4_SB(sb)->s_freeblocks_counter));
         es->s_free_inodes_count = cpu_to_le32(percpu_counter_sum_positive(
                                         &EXT4_SB(sb)->s_freeinodes_counter));
-
+        sb->s_dirt = 0;
         BUFFER_TRACE(sbh, "marking dirty");
         mark_buffer_dirty(sbh);
         if (sync) {
@@ -3210,7 +3209,6 @@ static void ext4_mark_recovery_complete(struct super_block *sb,
         if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER) &&
             sb->s_flags & MS_RDONLY) {
                 EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
-                sb->s_dirt = 0;
                 ext4_commit_super(sb, 1);
         }
         unlock_super(sb);
@@ -3271,10 +3269,8 @@ int ext4_force_commit(struct super_block *sb)
                 return 0;
 
         journal = EXT4_SB(sb)->s_journal;
-        if (journal) {
-                sb->s_dirt = 0;
+        if (journal)
                 ret = ext4_journal_force_commit(journal);
-        }
 
         return ret;
 }
@@ -3282,15 +3278,13 @@ int ext4_force_commit(struct super_block *sb)
 /*
  * Ext4 always journals updates to the superblock itself, so we don't
  * have to propagate any other updates to the superblock on disk at this
- * point.  (We can probably nuke this function altogether, and remove
- * any mention to sb->s_dirt in all of fs/ext4; eventual cleanup...)
+ * point if the journalling is enabled.
  */
 static void ext4_write_super(struct super_block *sb)
 {
         if (EXT4_SB(sb)->s_journal) {
                 if (mutex_trylock(&sb->s_lock) != 0)
                         BUG();
-                sb->s_dirt = 0;
         } else {
                 ext4_commit_super(sb, 1);
         }
@@ -3302,7 +3296,6 @@ static int ext4_sync_fs(struct super_block *sb, int wait)
         tid_t target;
 
         trace_mark(ext4_sync_fs, "dev %s wait %d", sb->s_id, wait);
-        sb->s_dirt = 0;
         if (EXT4_SB(sb)->s_journal) {
                 if (jbd2_journal_start_commit(EXT4_SB(sb)->s_journal,
                                               &target)) {
@@ -3324,7 +3317,6 @@ static int ext4_freeze(struct super_block *sb)
 {
         int error = 0;
         journal_t *journal;
-        sb->s_dirt = 0;
 
         if (!(sb->s_flags & MS_RDONLY)) {
                 journal = EXT4_SB(sb)->s_journal;