hfs: get rid of hfs_sync_super

This patch makes hfs stop using the VFS '->write_super()' method along with
the 's_dirt' superblock flag, because they are on their way out.

The whole "superblock write-out" VFS infrastructure is served by the
'sync_supers()' kernel thread, which wakes up every 5 (by default) seconds and
writes out all dirty superblocks using the '->write_super()' call-back.  But the
problem with this thread is that it wastes power by waking up the system every
5 seconds, even if there are no diry superblocks, or there are no client
file-systems which would need this (e.g., btrfs does not use
'->write_super()'). So we want to kill it completely and thus, we need to make
file-systems to stop using the '->write_super()' VFS service, and then remove
it together with the kernel thread.

Tested using fsstress from the LTP project.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

4 files changed, 48 insertions, 39 deletions

diff --git a/fs/hfs/extent.c b/fs/hfs/extent.c
index 2c16316d2917..a67955a0c36f 100644
--- a/fs/hfs/extent.c
+++ b/fs/hfs/extent.c
@@ -432,7 +432,7 @@ out:
                 if (inode->i_ino < HFS_FIRSTUSER_CNID)
                         set_bit(HFS_FLG_ALT_MDB_DIRTY, &HFS_SB(sb)->flags);
                 set_bit(HFS_FLG_MDB_DIRTY, &HFS_SB(sb)->flags);
-                sb->s_dirt = 1;
+                hfs_mark_mdb_dirty(sb);
         }
         return res;
 
diff --git a/fs/hfs/hfs_fs.h b/fs/hfs/hfs_fs.h
index 351561223ec3..8275175acf6e 100644
--- a/fs/hfs/hfs_fs.h
+++ b/fs/hfs/hfs_fs.h
@@ -14,6 +14,7 @@
 #include <linux/mutex.h>
 #include <linux/buffer_head.h>
 #include <linux/fs.h>
+#include <linux/workqueue.h>
 
 #include <asm/byteorder.h>
 #include <asm/uaccess.h>
@@ -143,6 +144,9 @@ struct hfs_sb_info {
         u16 blockoffset;
         int fs_div;
         struct super_block *sb;
+        int work_queued;                /* non-zero delayed work is queued */
+        struct delayed_work mdb_work;   /* MDB flush delayed work */
+        spinlock_t work_lock;           /* protects mdb_work and work_queued */
 };
 
 #define HFS_FLG_BITMAP_DIRTY    0
@@ -222,6 +226,9 @@ extern int hfs_compare_dentry(const struct dentry *parent,
 extern void hfs_asc2mac(struct super_block *, struct hfs_name *, struct qstr *);
 extern int hfs_mac2asc(struct super_block *, char *, const struct hfs_name *);
 
+/* super.c */
+extern void hfs_mark_mdb_dirty(struct super_block *sb);
+
 extern struct timezone sys_tz;
 
 /*
@@ -249,7 +256,7 @@ static inline const char *hfs_mdb_name(struct super_block *sb)
 static inline void hfs_bitmap_dirty(struct super_block *sb)
 {
         set_bit(HFS_FLG_BITMAP_DIRTY, &HFS_SB(sb)->flags);
-        sb->s_dirt = 1;
+        hfs_mark_mdb_dirty(sb);
 }
 
 #define sb_bread512(sb, sec, data) ({                   \
diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
index 90c1ccbff8e4..ee1bc55677f1 100644
--- a/fs/hfs/inode.c
+++ b/fs/hfs/inode.c
@@ -220,7 +220,7 @@ struct inode *hfs_new_inode(struct inode *dir, struct qstr *name, umode_t mode)
         insert_inode_hash(inode);
         mark_inode_dirty(inode);
         set_bit(HFS_FLG_MDB_DIRTY, &HFS_SB(sb)->flags);
-        sb->s_dirt = 1;
+        hfs_mark_mdb_dirty(sb);
 
         return inode;
 }
@@ -235,7 +235,7 @@ void hfs_delete_inode(struct inode *inode)
                 if (HFS_I(inode)->cat_key.ParID == cpu_to_be32(HFS_ROOT_CNID))
                         HFS_SB(sb)->root_dirs--;
                 set_bit(HFS_FLG_MDB_DIRTY, &HFS_SB(sb)->flags);
-                sb->s_dirt = 1;
+                hfs_mark_mdb_dirty(sb);
                 return;
         }
         HFS_SB(sb)->file_count--;
@@ -248,7 +248,7 @@ void hfs_delete_inode(struct inode *inode)
                 }
         }
         set_bit(HFS_FLG_MDB_DIRTY, &HFS_SB(sb)->flags);
-        sb->s_dirt = 1;
+        hfs_mark_mdb_dirty(sb);
 }
 
 void hfs_inode_read_fork(struct inode *inode, struct hfs_extent *ext,
@@ -644,10 +644,7 @@ static int hfs_file_fsync(struct file *filp, loff_t start, loff_t end,
 
         /* sync the superblock to buffers */
         sb = inode->i_sb;
-        if (sb->s_dirt) {
-                sb->s_dirt = 0;
-                hfs_mdb_commit(sb);
-        }
+        flush_delayed_work_sync(&HFS_SB(sb)->mdb_work);
         /* .. finally sync the buffers to disk */
         err = sync_blockdev(sb->s_bdev);
         if (!ret)
diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index 99c6239bc3a1..4eb873e0c07b 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -29,38 +29,9 @@ static struct kmem_cache *hfs_inode_cachep;
 
 MODULE_LICENSE("GPL");
 
-/*
- * hfs_write_super()
- *
- * Description:
- *   This function is called by the VFS only. When the filesystem
- *   is mounted r/w it updates the MDB on disk.
- * Input Variable(s):
- *   struct super_block *sb: Pointer to the hfs superblock
- * Output Variable(s):
- *   NONE
- * Returns:
- *   void
- * Preconditions:
- *   'sb' points to a "valid" (struct super_block).
- * Postconditions:
- *   The MDB is marked 'unsuccessfully unmounted' by clearing bit 8 of drAtrb
- *   (hfs_put_super() must set this flag!). Some MDB fields are updated
- *   and the MDB buffer is written to disk by calling hfs_mdb_commit().
- */
-static void hfs_write_super(struct super_block *sb)
-{
-        sb->s_dirt = 0;
-
-        /* sync everything to the buffers */
-        hfs_mdb_commit(sb);
-}
-
 static int hfs_sync_fs(struct super_block *sb, int wait)
 {
         hfs_mdb_commit(sb);
-        sb->s_dirt = 0;
-
         return 0;
 }
 
@@ -73,11 +44,44 @@ static int hfs_sync_fs(struct super_block *sb, int wait)
  */
 static void hfs_put_super(struct super_block *sb)
 {
+        cancel_delayed_work_sync(&HFS_SB(sb)->mdb_work);
         hfs_mdb_close(sb);
         /* release the MDB's resources */
         hfs_mdb_put(sb);
 }
 
+static void flush_mdb(struct work_struct *work)
+{
+        struct hfs_sb_info *sbi;
+        struct super_block *sb;
+
+        sbi = container_of(work, struct hfs_sb_info, mdb_work.work);
+        sb = sbi->sb;
+
+        spin_lock(&sbi->work_lock);
+        sbi->work_queued = 0;
+        spin_unlock(&sbi->work_lock);
+
+        hfs_mdb_commit(sb);
+}
+
+void hfs_mark_mdb_dirty(struct super_block *sb)
+{
+        struct hfs_sb_info *sbi = HFS_SB(sb);
+        unsigned long delay;
+
+        if (sb->s_flags & MS_RDONLY)
+                return;
+
+        spin_lock(&sbi->work_lock);
+        if (!sbi->work_queued) {
+                delay = msecs_to_jiffies(dirty_writeback_interval * 10);
+                queue_delayed_work(system_long_wq, &sbi->mdb_work, delay);
+                sbi->work_queued = 1;
+        }
+        spin_unlock(&sbi->work_lock);
+}
+
 /*
  * hfs_statfs()
  *
@@ -177,7 +181,6 @@ static const struct super_operations hfs_super_operations = {
         .write_inode    = hfs_write_inode,
         .evict_inode    = hfs_evict_inode,
         .put_super      = hfs_put_super,
-        .write_super    = hfs_write_super,
         .sync_fs        = hfs_sync_fs,
         .statfs         = hfs_statfs,
         .remount_fs     = hfs_remount,
@@ -382,6 +385,8 @@ static int hfs_fill_super(struct super_block *sb, void *data, int silent)
 
         sbi->sb = sb;
         sb->s_fs_info = sbi;
+        spin_lock_init(&sbi->work_lock);
+        INIT_DELAYED_WORK(&sbi->mdb_work, flush_mdb);
 
         res = -EINVAL;
         if (!parse_options((char *)data, sbi)) {