nilfs2: simplify life cycle management of nilfs object

This stops pre-allocating nilfs object in nilfs_get_sb routine, and
stops managing its life cycle by reference counting.

nilfs_find_or_create_nilfs() function, nilfs->ns_mount_mutex,
nilfs_objects list, and the reference counter will be removed through
the simplification.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

4 files changed, 31 insertions, 131 deletions

diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index 2ee6843c2e87..338858fc907c 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -117,7 +117,7 @@ static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
         if (copy_from_user(&cpmode, argp, sizeof(cpmode)))
                 goto out;
 
-        mutex_lock(&nilfs->ns_mount_mutex);
+        down_read(&inode->i_sb->s_umount);
 
         nilfs_transaction_begin(inode->i_sb, &ti, 0);
         ret = nilfs_cpfile_change_cpmode(
@@ -127,7 +127,7 @@ static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
         else
                 nilfs_transaction_commit(inode->i_sb); /* never fails */
 
-        mutex_unlock(&nilfs->ns_mount_mutex);
+        up_read(&inode->i_sb->s_umount);
 out:
         mnt_drop_write(filp->f_path.mnt);
         return ret;
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index 2e58e7c629b5..5893cb27c909 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -356,7 +356,7 @@ static void nilfs_put_super(struct super_block *sb)
                 up_write(&nilfs->ns_sem);
         }
 
-        put_nilfs(sbi->s_nilfs);
+        destroy_nilfs(nilfs);
         sbi->s_super = NULL;
         sb->s_fs_info = NULL;
         kfree(sbi);
@@ -836,15 +836,14 @@ static int nilfs_try_to_shrink_tree(struct dentry *root_dentry)
  * @sb: super_block
  * @data: mount options
  * @silent: silent mode flag
- * @nilfs: the_nilfs struct
  *
  * This function is called exclusively by nilfs->ns_mount_mutex.
  * So, the recovery process is protected from other simultaneous mounts.
  */
 static int
-nilfs_fill_super(struct super_block *sb, void *data, int silent,
-                 struct the_nilfs *nilfs)
+nilfs_fill_super(struct super_block *sb, void *data, int silent)
 {
+        struct the_nilfs *nilfs;
         struct nilfs_sb_info *sbi;
         struct nilfs_root *fsroot;
         __u64 cno;
@@ -855,14 +854,18 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
                 return -ENOMEM;
 
         sb->s_fs_info = sbi;
+        sbi->s_super = sb;
 
-        get_nilfs(nilfs);
+        nilfs = alloc_nilfs(sb->s_bdev);
+        if (!nilfs) {
+                err = -ENOMEM;
+                goto failed_sbi;
+        }
         sbi->s_nilfs = nilfs;
-        sbi->s_super = sb;
 
         err = init_nilfs(nilfs, sbi, (char *)data);
         if (err)
-                goto failed_sbi;
+                goto failed_nilfs;
 
         spin_lock_init(&sbi->s_inode_lock);
         INIT_LIST_HEAD(&sbi->s_dirty_files);
@@ -885,14 +888,14 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
 
         err = load_nilfs(nilfs, sbi);
         if (err)
-                goto failed_sbi;
+                goto failed_nilfs;
 
         cno = nilfs_last_cno(nilfs);
         err = nilfs_attach_checkpoint(sbi, cno, true, &fsroot);
         if (err) {
                 printk(KERN_ERR "NILFS: error loading last checkpoint "
                        "(checkpoint number=%llu).\n", (unsigned long long)cno);
-                goto failed_sbi;
+                goto failed_nilfs;
         }
 
         if (!(sb->s_flags & MS_RDONLY)) {
@@ -921,8 +924,10 @@ nilfs_fill_super(struct super_block *sb, void *data, int silent,
  failed_checkpoint:
         nilfs_put_root(fsroot);
 
+ failed_nilfs:
+        destroy_nilfs(nilfs);
+
  failed_sbi:
-        put_nilfs(nilfs);
         sb->s_fs_info = NULL;
         kfree(sbi);
         return err;
@@ -1077,7 +1082,6 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
         struct nilfs_super_data sd;
         struct super_block *s;
         fmode_t mode = FMODE_READ;
-        struct the_nilfs *nilfs;
         struct dentry *root_dentry;
         int err, s_new = false;
 
@@ -1095,18 +1099,10 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
                 goto failed;
         }
 
-        nilfs = find_or_create_nilfs(sd.bdev);
-        if (!nilfs) {
-                err = -ENOMEM;
-                goto failed;
-        }
-
-        mutex_lock(&nilfs->ns_mount_mutex);
-
         s = sget(fs_type, nilfs_test_bdev_super, nilfs_set_bdev_super, sd.bdev);
         if (IS_ERR(s)) {
                 err = PTR_ERR(s);
-                goto failed_unlock;
+                goto failed;
         }
 
         if (!s->s_root) {
@@ -1120,10 +1116,9 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
                 strlcpy(s->s_id, bdevname(sd.bdev, b), sizeof(s->s_id));
                 sb_set_blocksize(s, block_size(sd.bdev));
 
-                err = nilfs_fill_super(s, data, flags & MS_SILENT ? 1 : 0,
-                                       nilfs);
+                err = nilfs_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
                 if (err)
-                        goto cancel_new;
+                        goto failed_super;
 
                 s->s_flags |= MS_ACTIVE;
         } else if (!sd.cno) {
@@ -1153,17 +1148,12 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
 
         if (sd.cno) {
                 err = nilfs_attach_snapshot(s, sd.cno, &root_dentry);
-                if (err) {
-                        if (s_new)
-                                goto cancel_new;
+                if (err)
                         goto failed_super;
-                }
         } else {
                 root_dentry = dget(s->s_root);
         }
 
-        mutex_unlock(&nilfs->ns_mount_mutex);
-        put_nilfs(nilfs);
         if (!s_new)
                 close_bdev_exclusive(sd.bdev, mode);
 
@@ -1173,23 +1163,10 @@ nilfs_get_sb(struct file_system_type *fs_type, int flags,
 
  failed_super:
         deactivate_locked_super(s);
- failed_unlock:
-        mutex_unlock(&nilfs->ns_mount_mutex);
-        put_nilfs(nilfs);
- failed:
-        close_bdev_exclusive(sd.bdev, mode);
-        return err;
 
- cancel_new:
-        /* Abandoning the newly allocated superblock */
-        mutex_unlock(&nilfs->ns_mount_mutex);
-        put_nilfs(nilfs);
-        deactivate_locked_super(s);
-        /*
-         * This deactivate_locked_super() invokes close_bdev_exclusive().
-         * We must finish all post-cleaning before this call;
-         * put_nilfs() needs the block device.
-         */
+ failed:
+        if (!s_new)
+                close_bdev_exclusive(sd.bdev, mode);
         return err;
 }
 
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 960c28797bb2..6eeb4f072f83 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -35,9 +35,6 @@
 #include "segbuf.h"
 
 
-static LIST_HEAD(nilfs_objects);
-static DEFINE_SPINLOCK(nilfs_lock);
-
 static int nilfs_valid_sb(struct nilfs_super_block *sbp);
 
 void nilfs_set_last_segment(struct the_nilfs *nilfs,
@@ -61,16 +58,13 @@ void nilfs_set_last_segment(struct the_nilfs *nilfs,
 }
 
 /**
- * alloc_nilfs - allocate the_nilfs structure
+ * alloc_nilfs - allocate a nilfs object
  * @bdev: block device to which the_nilfs is related
  *
- * alloc_nilfs() allocates memory for the_nilfs and
- * initializes its reference count and locks.
- *
  * Return Value: On success, pointer to the_nilfs is returned.
  * On error, NULL is returned.
  */
-static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
+struct the_nilfs *alloc_nilfs(struct block_device *bdev)
 {
         struct the_nilfs *nilfs;
 
@@ -79,12 +73,9 @@ static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
                 return NULL;
 
         nilfs->ns_bdev = bdev;
-        atomic_set(&nilfs->ns_count, 1);
         atomic_set(&nilfs->ns_ndirtyblks, 0);
         init_rwsem(&nilfs->ns_sem);
-        mutex_init(&nilfs->ns_mount_mutex);
         init_rwsem(&nilfs->ns_writer_sem);
-        INIT_LIST_HEAD(&nilfs->ns_list);
         INIT_LIST_HEAD(&nilfs->ns_gc_inodes);
         spin_lock_init(&nilfs->ns_last_segment_lock);
         nilfs->ns_cptree = RB_ROOT;
@@ -95,67 +86,11 @@ static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
 }
 
 /**
- * find_or_create_nilfs - find or create nilfs object
- * @bdev: block device to which the_nilfs is related
- *
- * find_nilfs() looks up an existent nilfs object created on the
- * device and gets the reference count of the object.  If no nilfs object
- * is found on the device, a new nilfs object is allocated.
- *
- * Return Value: On success, pointer to the nilfs object is returned.
- * On error, NULL is returned.
- */
-struct the_nilfs *find_or_create_nilfs(struct block_device *bdev)
-{
-        struct the_nilfs *nilfs, *new = NULL;
-
- retry:
-        spin_lock(&nilfs_lock);
-        list_for_each_entry(nilfs, &nilfs_objects, ns_list) {
-                if (nilfs->ns_bdev == bdev) {
-                        get_nilfs(nilfs);
-                        spin_unlock(&nilfs_lock);
-                        if (new)
-                                put_nilfs(new);
-                        return nilfs; /* existing object */
-                }
-        }
-        if (new) {
-                list_add_tail(&new->ns_list, &nilfs_objects);
-                spin_unlock(&nilfs_lock);
-                return new; /* new object */
-        }
-        spin_unlock(&nilfs_lock);
-
-        new = alloc_nilfs(bdev);
-        if (new)
-                goto retry;
-        return NULL; /* insufficient memory */
-}
-
-/**
- * put_nilfs - release a reference to the_nilfs
- * @nilfs: the_nilfs structure to be released
- *
- * put_nilfs() decrements a reference counter of the_nilfs.
- * If the reference count reaches zero, the_nilfs is freed.
+ * destroy_nilfs - destroy nilfs object
+ * @nilfs: nilfs object to be released
  */
-void put_nilfs(struct the_nilfs *nilfs)
+void destroy_nilfs(struct the_nilfs *nilfs)
 {
-        spin_lock(&nilfs_lock);
-        if (!atomic_dec_and_test(&nilfs->ns_count)) {
-                spin_unlock(&nilfs_lock);
-                return;
-        }
-        list_del_init(&nilfs->ns_list);
-        spin_unlock(&nilfs_lock);
-
-        /*
-         * Increment of ns_count never occurs below because the caller
-         * of get_nilfs() holds at least one reference to the_nilfs.
-         * Thus its exclusion control is not required here.
-         */
-
         might_sleep();
         if (nilfs_loaded(nilfs)) {
                 nilfs_mdt_destroy(nilfs->ns_sufile);
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index 7b43693a69c5..1908dc7bbd8f 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -46,13 +46,10 @@ enum {
 /**
  * struct the_nilfs - struct to supervise multiple nilfs mount points
  * @ns_flags: flags
- * @ns_count: reference count
- * @ns_list: list head for nilfs_list
  * @ns_bdev: block device
  * @ns_bdi: backing dev info
  * @ns_writer: back pointer to writable nilfs_sb_info
  * @ns_sem: semaphore for shared states
- * @ns_mount_mutex: mutex protecting mount process of nilfs
  * @ns_writer_sem: semaphore protecting ns_writer attach/detach
  * @ns_sbh: buffer heads of on-disk super blocks
  * @ns_sbp: pointers to super block data
@@ -94,14 +91,11 @@ enum {
  */
 struct the_nilfs {
         unsigned long           ns_flags;
-        atomic_t                ns_count;
-        struct list_head        ns_list;
 
         struct block_device    *ns_bdev;
         struct backing_dev_info *ns_bdi;
         struct nilfs_sb_info   *ns_writer;
         struct rw_semaphore     ns_sem;
-        struct mutex            ns_mount_mutex;
         struct rw_semaphore     ns_writer_sem;
 
         /*
@@ -239,8 +233,8 @@ static inline int nilfs_sb_will_flip(struct the_nilfs *nilfs)
 }
 
 void nilfs_set_last_segment(struct the_nilfs *, sector_t, u64, __u64);
-struct the_nilfs *find_or_create_nilfs(struct block_device *);
-void put_nilfs(struct the_nilfs *);
+struct the_nilfs *alloc_nilfs(struct block_device *bdev);
+void destroy_nilfs(struct the_nilfs *nilfs);
 int init_nilfs(struct the_nilfs *, struct nilfs_sb_info *, char *);
 int load_nilfs(struct the_nilfs *, struct nilfs_sb_info *);
 int nilfs_discard_segments(struct the_nilfs *, __u64 *, size_t);
@@ -256,12 +250,6 @@ void nilfs_fall_back_super_block(struct the_nilfs *);
 void nilfs_swap_super_block(struct the_nilfs *);
 
 
-static inline void get_nilfs(struct the_nilfs *nilfs)
-{
-        /* Caller must have at least one reference of the_nilfs. */
-        atomic_inc(&nilfs->ns_count);
-}
-
 static inline void nilfs_get_root(struct nilfs_root *root)
 {
         atomic_inc(&root->count);