cleanup sync_supers

Merge the write_super helper into sync_super and move the check for
->write_super earlier so that we can avoid grabbing a reference to
a superblock that doesn't have it.

While we're at it also add a little comment documenting sync_supers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 15 insertions, 12 deletions

diff --git a/fs/super.c b/fs/super.c
index d9a29d5b1d28..cb19fffc7681 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -399,16 +399,14 @@ void drop_super(struct super_block *sb)
 
 EXPORT_SYMBOL(drop_super);
 
-static inline void write_super(struct super_block *sb)
-{
-        lock_super(sb);
-        if (sb->s_root && sb->s_dirt)
-                if (sb->s_op->write_super)
-                        sb->s_op->write_super(sb);
-        unlock_super(sb);
-}
-
-/*
+/**
+ * sync_supers - helper for periodic superblock writeback
+ *
+ * Call the write_super method if present on all dirty superblocks in
+ * the system.  This is for the periodic writeback used by most older
+ * filesystems.  For data integrity superblock writeback use
+ * sync_filesystems() instead.
+ *
  * Note: check the dirty flag before waiting, so we don't
  * hold up the sync while mounting a device. (The newly
  * mounted device won't need syncing.)
@@ -420,12 +418,17 @@ void sync_supers(void)
         spin_lock(&sb_lock);
 restart:
         list_for_each_entry(sb, &super_blocks, s_list) {
-                if (sb->s_dirt) {
+                if (sb->s_op->write_super && sb->s_dirt) {
                         sb->s_count++;
                         spin_unlock(&sb_lock);
+
                         down_read(&sb->s_umount);
-                        write_super(sb);
+                        lock_super(sb);
+                        if (sb->s_root && sb->s_dirt)
+                                sb->s_op->write_super(sb);
+                        unlock_super(sb);
                         up_read(&sb->s_umount);
+
                         spin_lock(&sb_lock);
                         if (__put_super_and_need_restart(sb))
                                 goto restart;