f2fs: avoid balanc_fs during evict_inode

1. Background

Previously, if f2fs tries to move data blocks of an *evicting* inode during the
cleaning process, it stops the process incompletely and then restarts the whole
process, since it needs a locked inode to grab victim data pages in its address
space. In order to get a locked inode, iget_locked() by f2fs_iget() is normally
used, but, it waits if the inode is on freeing.

So, here is a deadlock scenario.
1. f2fs_evict_inode()       <- inode "A"
  2. f2fs_balance_fs()
    3. f2fs_gc()
      4. gc_data_segment()
        5. f2fs_iget()      <- inode "A" too!

If step #1 and #5 treat a same inode "A", step #5 would fall into deadlock since
the inode "A" is on freeing. In order to resolve this, f2fs_iget_nowait() which
skips __wait_on_freeing_inode() was introduced in step #5, and stops f2fs_gc()
to complete f2fs_evict_inode().

1. f2fs_evict_inode()           <- inode "A"
  2. f2fs_balance_fs()
    3. f2fs_gc()
      4. gc_data_segment()
        5. f2fs_iget_nowait()   <- inode "A", then stop f2fs_gc() w/ -ENOENT

2. Problem and Solution

In the above scenario, however, f2fs cannot finish f2fs_evict_inode() only if:
 o there are not enough free sections, and
 o f2fs_gc() tries to move data blocks of the *evicting* inode repeatedly.

So, the final solution is to use f2fs_iget() and remove f2fs_balance_fs() in
f2fs_evict_inode().
The f2fs_evict_inode() actually truncates all the data and node blocks, which
means that it doesn't produce any dirty node pages accordingly.
So, we don't need to do f2fs_balance_fs() in practical.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/f2fs.h

@@ -847,7 +847,6 @@ long f2fs_ioctl(struct file *, unsigned int, unsigned long);
  * inode.c
  */
 void f2fs_set_inode_flags(struct inode *);
-struct inode *f2fs_iget_nowait(struct super_block *, unsigned long);
 struct inode *f2fs_iget(struct super_block *, unsigned long);
 void update_inode(struct inode *, struct page *);
 int f2fs_write_inode(struct inode *, struct writeback_control *);

fs/f2fs/file.c

@@ -298,8 +298,6 @@ void f2fs_truncate(struct inode *inode)
 		inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 		mark_inode_dirty(inode);
 	}
-
-	f2fs_balance_fs(F2FS_SB(inode->i_sb));
 }
 
 static int f2fs_getattr(struct vfsmount *mnt,
@@ -356,6 +354,7 @@ int f2fs_setattr(struct dentry *dentry, struct iattr *attr)
 			attr->ia_size != i_size_read(inode)) {
 		truncate_setsize(inode, attr->ia_size);
 		f2fs_truncate(inode);
+		f2fs_balance_fs(F2FS_SB(inode->i_sb));
 	}
 
 	__setattr_copy(inode, attr);

fs/f2fs/gc.c

@@ -579,7 +579,7 @@ static int gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 		ofs_in_node = le16_to_cpu(entry->ofs_in_node);
 
 		if (phase == 2) {
-			inode = f2fs_iget_nowait(sb, dni.ino);
+			inode = f2fs_iget(sb, dni.ino);
 			if (IS_ERR(inode))
 				continue;
 

fs/f2fs/inode.c

@@ -16,11 +16,6 @@
 #include "f2fs.h"
 #include "node.h"
 
-struct f2fs_iget_args {
-	u64 ino;
-	int on_free;
-};
-
 void f2fs_set_inode_flags(struct inode *inode)
 {
 	unsigned int flags = F2FS_I(inode)->i_flags;
@@ -40,34 +35,6 @@ void f2fs_set_inode_flags(struct inode *inode)
 		inode->i_flags |= S_DIRSYNC;
 }
 
-static int f2fs_iget_test(struct inode *inode, void *data)
-{
-	struct f2fs_iget_args *args = data;
-
-	if (inode->i_ino != args->ino)
-		return 0;
-	if (inode->i_state & (I_FREEING | I_WILL_FREE)) {
-		args->on_free = 1;
-		return 0;
-	}
-	return 1;
-}
-
-struct inode *f2fs_iget_nowait(struct super_block *sb, unsigned long ino)
-{
-	struct f2fs_iget_args args = {
-		.ino = ino,
-		.on_free = 0
-	};
-	struct inode *inode = ilookup5(sb, ino, f2fs_iget_test, &args);
-
-	if (inode)
-		return inode;
-	if (!args.on_free)
-		return f2fs_iget(sb, ino);
-	return ERR_PTR(-ENOENT);
-}
-
 static int do_read_inode(struct inode *inode)
 {
 	struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);

fs/f2fs/recovery.c

@@ -226,7 +226,7 @@ static void check_index_in_prev_nodes(struct f2fs_sb_info *sbi,
 	f2fs_put_page(node_page, 1);
 
 	/* Deallocate previous index in the node page */
-	inode = f2fs_iget_nowait(sbi->sb, ino);
+	inode = f2fs_iget(sbi->sb, ino);
 	if (IS_ERR(inode))
 		return;