From e8f179b9dc92fe91d7379a3ac330a57a2ef9fc87 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Fri, 13 Aug 2010 14:45:16 +0200
Subject: [PATCH] writeback: Alternate fix for umount regression

Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
---
 fs/fs-writeback.c           |   18 +++++++++++-------
 fs/sync.c                   |    2 +-
 fs/ubifs/budget.c           |    2 +-
 include/linux/backing-dev.h |    2 +-
 include/linux/writeback.h   |    4 +++-
 mm/page-writeback.c         |    2 +-
 6 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 460e5b7..bc87976 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -45,6 +45,7 @@ struct wb_writeback_args {
 	int for_kupdate:1;
 	int range_cyclic:1;
 	int for_background:1;
+	int locked:1;
 };
 
 /*
@@ -252,13 +253,14 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi,
  *
  */
 void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-			 long nr_pages)
+			 long nr_pages, int locked)
 {
 	struct wb_writeback_args args = {
 		.sb		= sb,
 		.sync_mode	= WB_SYNC_NONE,
 		.nr_pages	= nr_pages,
 		.range_cyclic	= 1,
+		.locked		= locked,
 	};
 
 	/*
@@ -585,7 +587,7 @@ static int pin_sb_for_writeback(struct writeback_control *wbc,
 	/*
 	 * Caller must already hold the ref for this
 	 */
-	if (wbc->sync_mode == WB_SYNC_ALL) {
+	if (wbc->sync_mode == WB_SYNC_ALL || wbc->locked) {
 		WARN_ON(!rwsem_is_locked(&sb->s_umount));
 		return 0;
 	}
@@ -758,6 +760,7 @@ static long wb_writeback(struct bdi_writeback *wb,
 		.older_than_this	= NULL,
 		.for_kupdate		= args->for_kupdate,
 		.range_cyclic		= args->range_cyclic,
+		.locked			= args->locked,
 	};
 	unsigned long oldest_jif;
 	long wrote = 0;
@@ -912,7 +915,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
 		 * If this isn't a data integrity operation, just notify
 		 * that we have seen this work and we are now starting it.
 		 */
-		if (args.sync_mode == WB_SYNC_NONE)
+		if (args.sync_mode == WB_SYNC_NONE && !args.locked)
 			wb_clear_pending(wb, work);
 
 		wrote += wb_writeback(wb, &args);
@@ -921,7 +924,7 @@ long wb_do_writeback(struct bdi_writeback *wb, int force_wait)
 		 * This is a data integrity writeback, so only do the
 		 * notification when we have completed the work.
 		 */
-		if (args.sync_mode == WB_SYNC_ALL)
+		if (args.sync_mode == WB_SYNC_ALL || args.locked)
 			wb_clear_pending(wb, work);
 	}
 
@@ -1206,13 +1209,14 @@ static void wait_sb_inodes(struct super_block *sb)
 /**
  * writeback_inodes_sb	-	writeback dirty inodes from given super_block
  * @sb: the superblock
+ * @locked: sb already pinned
  *
  * Start writeback on some inodes on this super_block. No guarantees are made
  * on how many (if any) will be written, and this function does not wait
  * for IO completion of submitted IO. The number of pages submitted is
  * returned.
  */
-void writeback_inodes_sb(struct super_block *sb)
+void writeback_inodes_sb(struct super_block *sb, int locked)
 {
 	unsigned long nr_dirty = global_page_state(NR_FILE_DIRTY);
 	unsigned long nr_unstable = global_page_state(NR_UNSTABLE_NFS);
@@ -1221,7 +1225,7 @@ void writeback_inodes_sb(struct super_block *sb)
 	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);
+	bdi_start_writeback(sb->s_bdi, sb, nr_to_write, locked);
 }
 EXPORT_SYMBOL(writeback_inodes_sb);
 
@@ -1235,7 +1239,7 @@ EXPORT_SYMBOL(writeback_inodes_sb);
 int writeback_inodes_sb_if_idle(struct super_block *sb)
 {
 	if (!writeback_in_progress(sb->s_bdi)) {
-		writeback_inodes_sb(sb);
+		writeback_inodes_sb(sb, 0);
 		return 1;
 	} else
 		return 0;
diff --git a/fs/sync.c b/fs/sync.c
index d104591..41d543e 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -37,7 +37,7 @@ static int __sync_filesystem(struct super_block *sb, int wait)
 	/* Avoid doing twice syncing and cache pruning for quota sync */
 	if (!wait) {
 		writeout_quota_sb(sb, -1);
-		writeback_inodes_sb(sb);
+		writeback_inodes_sb(sb, 1);
 	} else {
 		sync_quota_sb(sb, -1);
 		sync_inodes_sb(sb);
diff --git a/fs/ubifs/budget.c b/fs/ubifs/budget.c
index 076ca50..d16a8eb 100644
--- a/fs/ubifs/budget.c
+++ b/fs/ubifs/budget.c
@@ -62,7 +62,7 @@
  */
 static void shrink_liability(struct ubifs_info *c, int nr_to_write)
 {
-	writeback_inodes_sb(c->vfs_sb);
+	writeback_inodes_sb(c->vfs_sb, 0);
 }
 
 /**
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index b449e73..ce997ba 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -102,7 +102,7 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
 void bdi_start_writeback(struct backing_dev_info *bdi, struct super_block *sb,
-				long nr_pages);
+				long nr_pages, int locked);
 int bdi_writeback_task(struct bdi_writeback *wb);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
 
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index dc52482..4578dc1 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -52,6 +52,8 @@ struct writeback_control {
 	unsigned for_reclaim:1;		/* Invoked from the page allocator */
 	unsigned range_cyclic:1;	/* range_start is cyclic */
 	unsigned more_io:1;		/* more io to be dispatched */
+	unsigned locked:1;		/* sb pinned for WB_SYNC_NONE */
+
 	/*
 	 * write_cache_pages() won't update wbc->nr_to_write and
 	 * mapping->writeback_index if no_nrwrite_index_update
@@ -68,7 +70,7 @@ struct writeback_control {
  */	
 struct bdi_writeback;
 int inode_wait(void *);
-void writeback_inodes_sb(struct super_block *);
+void writeback_inodes_sb(struct super_block *, int);
 int writeback_inodes_sb_if_idle(struct super_block *);
 void sync_inodes_sb(struct super_block *);
 void writeback_inodes_wbc(struct writeback_control *wbc);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2c5d792..e73dbb7 100644
--- a/mm/page-writeback.c
+++ b/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);
+		bdi_start_writeback(bdi, NULL, 0, 0);
 }
 
 void set_page_dirty_balance(struct page *page, int page_mkwrite)
-- 
1.7.0.4

