3 files changed, 12 insertions, 26 deletions

diff --git a/fs/nilfs2/mdt.c b/fs/nilfs2/mdt.c
index 2dfd47714ae..a5cd80162dc 100644
--- a/fs/nilfs2/mdt.c
+++ b/fs/nilfs2/mdt.c
@@ -402,6 +402,7 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
 	struct inode *inode = container_of(page->mapping,
 					   struct inode, i_data);
 	struct super_block *sb = inode->i_sb;
+	struct the_nilfs *nilfs = NILFS_MDT(inode)->mi_nilfs;
 	struct nilfs_sb_info *writer = NULL;
 	int err = 0;
 
@@ -411,9 +412,10 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
 	if (page->mapping->assoc_mapping)
 		return 0; /* Do not request flush for shadow page cache */
 	if (!sb) {
-		writer = nilfs_get_writer(NILFS_MDT(inode)->mi_nilfs);
+		down_read(&nilfs->ns_writer_sem);
+		writer = nilfs->ns_writer;
 		if (!writer) {
-			nilfs_put_writer(NILFS_MDT(inode)->mi_nilfs);
+			up_read(&nilfs->ns_writer_sem);
 			return -EROFS;
 		}
 		sb = writer->s_super;
@@ -425,7 +427,7 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
 		nilfs_flush_segment(sb, inode->i_ino);
 
 	if (writer)
-		nilfs_put_writer(NILFS_MDT(inode)->mi_nilfs);
+		up_read(&nilfs->ns_writer_sem);
 	return err;
 }
 
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 8b888982571..0c4573653b8 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -68,12 +68,11 @@ static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
 
 	nilfs->ns_bdev = bdev;
 	atomic_set(&nilfs->ns_count, 1);
-	atomic_set(&nilfs->ns_writer_refcount, -1);
 	atomic_set(&nilfs->ns_ndirtyblks, 0);
 	init_rwsem(&nilfs->ns_sem);
 	init_rwsem(&nilfs->ns_super_sem);
 	mutex_init(&nilfs->ns_mount_mutex);
-	mutex_init(&nilfs->ns_writer_mutex);
+	init_rwsem(&nilfs->ns_writer_sem);
 	INIT_LIST_HEAD(&nilfs->ns_list);
 	INIT_LIST_HEAD(&nilfs->ns_supers);
 	spin_lock_init(&nilfs->ns_last_segment_lock);
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index 1b9caafb866..fa3a1dfe405 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -50,8 +50,7 @@ enum {
  * @ns_sem: semaphore for shared states
  * @ns_super_sem: semaphore for global operations across super block instances
  * @ns_mount_mutex: mutex protecting mount process of nilfs
- * @ns_writer_mutex: mutex protecting ns_writer attach/detach
- * @ns_writer_refcount: number of referrers on ns_writer
+ * @ns_writer_sem: semaphore protecting ns_writer attach/detach
  * @ns_current: back pointer to current mount
  * @ns_sbh: buffer heads of on-disk super blocks
  * @ns_sbp: pointers to super block data
@@ -100,8 +99,7 @@ struct the_nilfs {
 	struct rw_semaphore	ns_sem;
 	struct rw_semaphore	ns_super_sem;
 	struct mutex		ns_mount_mutex;
-	struct mutex		ns_writer_mutex;
-	atomic_t		ns_writer_refcount;
+	struct rw_semaphore	ns_writer_sem;
 
 	/*
 	 * components protected by ns_super_sem
@@ -221,34 +219,21 @@ static inline void get_nilfs(struct the_nilfs *nilfs)
 	atomic_inc(&nilfs->ns_count);
 }
 
-static inline struct nilfs_sb_info *nilfs_get_writer(struct the_nilfs *nilfs)
-{
-	if (atomic_inc_and_test(&nilfs->ns_writer_refcount))
-		mutex_lock(&nilfs->ns_writer_mutex);
-	return nilfs->ns_writer;
-}
-
-static inline void nilfs_put_writer(struct the_nilfs *nilfs)
-{
-	if (atomic_add_negative(-1, &nilfs->ns_writer_refcount))
-		mutex_unlock(&nilfs->ns_writer_mutex);
-}
-
 static inline void
 nilfs_attach_writer(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
 {
-	mutex_lock(&nilfs->ns_writer_mutex);
+	down_write(&nilfs->ns_writer_sem);
 	nilfs->ns_writer = sbi;
-	mutex_unlock(&nilfs->ns_writer_mutex);
+	up_write(&nilfs->ns_writer_sem);
 }
 
 static inline void
 nilfs_detach_writer(struct the_nilfs *nilfs, struct nilfs_sb_info *sbi)
 {
-	mutex_lock(&nilfs->ns_writer_mutex);
+	down_write(&nilfs->ns_writer_sem);
 	if (sbi == nilfs->ns_writer)
 		nilfs->ns_writer = NULL;
-	mutex_unlock(&nilfs->ns_writer_mutex);
+	up_write(&nilfs->ns_writer_sem);
 }
 
 static inline void nilfs_put_sbinfo(struct nilfs_sb_info *sbi)