[PATCH 1/5] vfs: Make sync(1) writeout also block device inodes

[Jan Kara <jack@suse.cz>]

In case block device does not have filesystem mounted on it, sync(1) will just
ignore it and doesn't writeout dirty pages because it iterates over filesystems
with s_bdi != noop_backing_dev_info and thus it avoids blockdev_superblock.
Since it's unexpected that sync doesn't writeout dirty data for block devices
be nice to users and change the behavior to do so.

This requires a change to how syncing is done. We now first traverse all
superblocks with s_bdi != noop_backing_dev_info, writeout their inodes and
call sync_fs and when this is done, we traverse all block devices and sync
them.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/sync.c |   70 +++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/fs/sync.c b/fs/sync.c
index c38ec16..f8f21d9 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -23,20 +23,13 @@
 
 /*
  * Do the filesystem syncing work. For simple filesystems
- * writeback_inodes_sb(sb) just dirties buffers with inodes so we have to
- * submit IO for these buffers via __sync_blockdev(). This also speeds up the
- * wait == 1 case since in that case write_inode() functions do
+ * writeback_inodes_sb(sb) just dirties buffers with inodes so the caller has
+ * to additionally submit IO for these buffers via __sync_blockdev(). This also
+ * speeds up the wait == 1 case since in that case write_inode() functions do
  * sync_dirty_buffer() and thus effectively write one block at a time.
  */
-static int __sync_filesystem(struct super_block *sb, int wait)
+static void __sync_filesystem(struct super_block *sb, int wait)
 {
-	/*
-	 * This should be safe, as we require bdi backing to actually
-	 * write out data in the first place
-	 */
-	if (sb->s_bdi == &noop_backing_dev_info)
-		return 0;
-
 	if (sb->s_qcop && sb->s_qcop->quota_sync)
 		sb->s_qcop->quota_sync(sb, -1, wait);
 
@@ -47,7 +40,6 @@ static int __sync_filesystem(struct super_block *sb, int wait)
 
 	if (sb->s_op->sync_fs)
 		sb->s_op->sync_fs(sb, wait);
-	return __sync_blockdev(sb->s_bdev, wait);
 }
 
 /*
@@ -71,16 +63,26 @@ int sync_filesystem(struct super_block *sb)
 	if (sb->s_flags & MS_RDONLY)
 		return 0;
 
-	ret = __sync_filesystem(sb, 0);
+	/*
+	 * This should be safe, as we require bdi backing to actually
+	 * write out data in the first place.
+	 */
+	if (sb->s_bdi == &noop_backing_dev_info)
+		return 0;
+
+	__sync_filesystem(sb, 0);
+	ret = __sync_blockdev(sb->s_bdev, 0);
 	if (ret < 0)
 		return ret;
-	return __sync_filesystem(sb, 1);
+	__sync_filesystem(sb, 1);
+	return __sync_blockdev(sb->s_bdev, 1);
 }
 EXPORT_SYMBOL_GPL(sync_filesystem);
 
 static void sync_one_sb(struct super_block *sb, void *arg)
 {
-	if (!(sb->s_flags & MS_RDONLY))
+	/* Avoid read-only filesystems and filesystems without backing device */
+	if (!(sb->s_flags & MS_RDONLY) && sb->s_bdi != &noop_backing_dev_info)
 		__sync_filesystem(sb, *(int *)arg);
 }
 /*
@@ -92,6 +94,42 @@ static void sync_filesystems(int wait)
 	iterate_supers(sync_one_sb, &wait);
 }
 
+static void sync_all_bdevs(int wait)
+{
+	struct inode *inode, *old_inode = NULL;
+
+	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) {
+			spin_unlock(&inode->i_lock);
+			continue;
+		}
+		__iget(inode);
+		spin_unlock(&inode->i_lock);
+		spin_unlock(&inode_sb_list_lock);
+		/*
+		 * We hold a reference to 'inode' so it couldn't have been
+		 * removed from s_inodes list while we dropped the
+		 * inode_sb_list_lock.  We cannot iput the inode now as we can
+		 * be holding the last reference and we cannot iput it under
+		 * inode_sb_list_lock. So we keep the reference and iput it
+		 * later.
+		 */
+		iput(old_inode);
+		old_inode = inode;
+
+		__sync_blockdev(I_BDEV(inode), wait);
+
+		spin_lock(&inode_sb_list_lock);
+	}
+	spin_unlock(&inode_sb_list_lock);
+	iput(old_inode);
+}
+
 /*
  * sync everything.  Start out by waking pdflush, because that writes back
  * all queues in parallel.
@@ -101,6 +139,8 @@ SYSCALL_DEFINE0(sync)
 	wakeup_flusher_threads(0);
 	sync_filesystems(0);
 	sync_filesystems(1);
+	sync_all_bdevs(0);
+	sync_all_bdevs(1);
 	if (unlikely(laptop_mode))
 		laptop_sync_completion();
 	return 0;
-- 
1.7.1