[PATCH] fs: Move check for mappings without pages from iterate_bdevs()

[Jan Kara <jack@suse.cz>]

Currently, iterate_bdevs() skips block devices without any pages in page
cache. That is fine for current use by sync(2) but may be rather surprising
for possible future users. So move the checks from iterate_bdevs() to
callback functions used by sync(2).

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/block_dev.c |    5 +----
 fs/sync.c      |   12 ++++++++++--
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 38e721b..1631cbd 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1720,11 +1720,8 @@ void iterate_bdevs(void (*func)(struct block_device *, void *), void *arg)
 
 	spin_lock(&inode_sb_list_lock);
 	list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) {
-		struct address_space *mapping = inode->i_mapping;
-
 		spin_lock(&inode->i_lock);
-		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW) ||
-		    mapping->nrpages == 0) {
+		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
 			spin_unlock(&inode->i_lock);
 			continue;
 		}
diff --git a/fs/sync.c b/fs/sync.c
index eb8722d..536a272 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -81,12 +81,20 @@ static void sync_fs_one_sb(struct super_block *sb, void *arg)
 
 static void fdatawrite_one_bdev(struct block_device *bdev, void *arg)
 {
-	filemap_fdatawrite(bdev->bd_inode->i_mapping);
+	struct address_space *mapping = bdev->bd_inode->i_mapping;
+
+	if (mapping->nrpages == 0)
+		return;
+	filemap_fdatawrite(mapping);
 }
 
 static void fdatawait_one_bdev(struct block_device *bdev, void *arg)
 {
-	filemap_fdatawait(bdev->bd_inode->i_mapping);
+	struct address_space *mapping = bdev->bd_inode->i_mapping;
+
+	if (mapping->nrpages == 0)
+		return;
+	filemap_fdatawait(mapping);
 }
 
 /*
-- 
1.7.1