Revert "writeback: fix WB_SYNC_NONE writeback from umount"

This reverts commit e913fc82.

We are investigating a hang associated with the WB_SYNC_NONE changes,
so revert them for now.

Conflicts:

	fs/fs-writeback.c
	mm/page-writeback.c
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

fs/fs-writeback.c

@@ -45,7 +45,6 @@ struct wb_writeback_args {
 	unsigned int for_kupdate:1;
 	unsigned int range_cyclic:1;
 	unsigned int for_background:1;
-	unsigned int sb_pinned:1;
 };
 
 /*
@@ -231,11 +230,6 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
 		.sync_mode	= WB_SYNC_ALL,
 		.nr_pages	= LONG_MAX,
 		.range_cyclic	= 0,
-		/*
-		 * Setting sb_pinned is not necessary for WB_SYNC_ALL, but
-		 * lets make it explicitly clear.
-		 */
-		.sb_pinned	= 1,
 	};
 	struct bdi_work work;
 
@@ -251,23 +245,21 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
  * @bdi: the backing device to write from
  * @sb: write inodes from this super_block
  * @nr_pages: the number of pages to write
- * @sb_locked: caller already holds sb umount sem.
  *
  * Description:
  *   This does WB_SYNC_NONE opportunistic writeback. The IO is only
  *   started when this function returns, we make no guarentees on
- *   completion. Caller specifies whether sb umount sem is held already or not.
+ *   completion. Caller need not hold sb s_umount semaphore.
  *
  */
 void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-			 long nr_pages, int sb_locked)
+			 long nr_pages)
 {
 	struct wb_writeback_args args = {
 		.sb		= sb,
 		.sync_mode	= WB_SYNC_NONE,
 		.nr_pages	= nr_pages,
 		.range_cyclic	= 1,
-		.sb_pinned	= sb_locked,
 	};
 
 	/*
@@ -592,7 +584,7 @@ static enum sb_pin_state pin_sb_for_writeback(struct writeback_control *wbc,
 	/*
 	 * Caller must already hold the ref for this
 	 */
-	if (wbc->sync_mode == WB_SYNC_ALL || wbc->sb_pinned) {
+	if (wbc->sync_mode == WB_SYNC_ALL) {
 		WARN_ON(!rwsem_is_locked(&sb->s_umount));
 		return SB_NOT_PINNED;
 	}
@@ -766,7 +758,6 @@ static long wb_writeback(struct bdi_writeback *wb,
 		.for_kupdate		= args->for_kupdate,
 		.for_background		= args->for_background,
 		.range_cyclic		= args->range_cyclic,
-		.sb_pinned		= args->sb_pinned,
 	};
 	unsigned long oldest_jif;
 	long wrote = 0;
@@ -1214,18 +1205,6 @@ static void wait_sb_inodes(struct super_block *sb)
 	iput(old_inode);
 }
 
-static void __writeback_inodes_sb(struct super_block *sb, int sb_locked)
-{
-	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
-	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
-	long nr_to_write;
-
-	nr_to_write = nr_dirty + nr_unstable +
-			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
-
-	bdi_start_writeback(sb->s_bdi, sb, nr_to_write, sb_locked);
-}
-
 /**
  * writeback_inodes_sb	-	writeback dirty inodes from given super_block
  * @sb: the superblock
@@ -1237,21 +1216,16 @@ static void __writeback_inodes_sb(struct super_block *sb, int sb_locked)
  */
 void writeback_inodes_sb(struct super_block *sb)
 {
-	__writeback_inodes_sb(sb, 0);
-}
-EXPORT_SYMBOL(writeback_inodes_sb);
+	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
+	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
+	long nr_to_write;
 
-/**
- * writeback_inodes_sb_locked	- writeback dirty inodes from given super_block
- * @sb: the superblock
- *
- * Like writeback_inodes_sb(), except the caller already holds the
- * sb umount sem.
- */
-void writeback_inodes_sb_locked(struct super_block *sb)
-{
-	__writeback_inodes_sb(sb, 1);
+	nr_to_write = nr_dirty + nr_unstable +
+			(inodes_stat.nr_inodes - inodes_stat.nr_unused);
+
+	bdi_start_writeback(sb->s_bdi, sb, nr_to_write);
 }
+EXPORT_SYMBOL(writeback_inodes_sb);
 
 /**
  * writeback_inodes_sb_if_idle	-	start writeback if none underway

fs/sync.c

@@ -42,7 +42,7 @@ static int __sync_filesystem(struct super_block *sb, int wait)
 	if (wait)
 		sync_inodes_sb(sb);
 	else
-		writeback_inodes_sb_locked(sb);
+		writeback_inodes_sb(sb);
 
 	if (sb->s_op->sync_fs)
 		sb->s_op->sync_fs(sb, wait);

include/linux/backing-dev.h

@@ -106,7 +106,7 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
 int bdi_setup_and_register(struct backing_dev_info *, char *, unsigned int);
 void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-				long nr_pages, int sb_locked);
+				long nr_pages);
 int bdi_writeback_task(struct bdi_writeback *wb);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
 void bdi_arm_supers_timer(void);

include/linux/writeback.h

@@ -65,15 +65,6 @@ struct writeback_control {
 	 * so we use a single control to update them
 	 */
 	unsigned no_nrwrite_index_update:1;
-
-	/*
-	 * For WB_SYNC_ALL, the sb must always be pinned. For WB_SYNC_NONE,
-	 * the writeback code will pin the sb for the caller. However,
-	 * for eg umount, the caller does WB_SYNC_NONE but already has
-	 * the sb pinned. If the below is set, caller already has the
-	 * sb pinned.
-	 */
-	unsigned sb_pinned:1;
 };
 
 /*
@@ -82,7 +73,6 @@ struct writeback_control {
 struct bdi_writeback;
 int inode_wait(void *);
 void writeback_inodes_sb(struct super_block *);
-void writeback_inodes_sb_locked(struct super_block *);
 int writeback_inodes_sb_if_idle(struct super_block *);
 void sync_inodes_sb(struct super_block *);
 void writeback_inodes_wbc(struct writeback_control *wbc);

mm/page-writeback.c

@@ -597,7 +597,7 @@ static void balance_dirty_pages(struct address_space *mapping,
 	    (!laptop_mode && ((global_page_state(NR_FILE_DIRTY)
 			       + global_page_state(NR_UNSTABLE_NFS))
 					  > background_thresh)))
-		bdi_start_writeback(bdi, NULL, 0, 0);
+		bdi_start_writeback(bdi, NULL, 0);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)
@@ -707,7 +707,7 @@ void laptop_mode_timer_fn(unsigned long data)
 	 */
 
 	if (bdi_has_dirty_io(&q->backing_dev_info))
-		bdi_start_writeback(&q->backing_dev_info, NULL, nr_pages, 0);
+		bdi_start_writeback(&q->backing_dev_info, NULL, nr_pages);
 }
 
 /*