[PATCH] f2fs: use f2fs_iget_nowait again

[Jaegeuk Kim <jaegeuk.kim@samsung.com>]

Previously, I removed f2fs_iget_nowait() through the commit:
d4686d56ec912d55fd8a9d6d509de50de24e90ab
f2fs: avoid balanc_fs during evict_inode.

But, there is another error scenario as follows.

Thread 1:
- writeback_sb_inodes
 - do_writepages
  - f2fs_write_data_pages
   - write_cache_pages
    - f2fs_write_data_page
     - f2fs_balance_fs
      - wait mutex_lock(gc_mutex)

Thread 2:
- f2fs_balance_fs
 - mutex_lock(gc_mutex)
 - f2fs_gc
  - f2fs_iget
   - wait iget_locked(inode->i_lock)

Thread 3:
- do_unlinkat
 - iput
  - lock(inode->i_lock)
   - evict
    - inode_wait_for_writeback

The above three threads are able to incur deadlock condition.
In order to address this issue, let's use f2fs_iget_nowait again in f2fs_gc so
that thread 2 doesn't need to wait for inode->i_lock.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
---
 fs/f2fs/f2fs.h  |  1 +
 fs/f2fs/gc.c    |  2 +-
 fs/f2fs/inode.c | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 20aab02..6fd872f 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -893,6 +893,7 @@ long f2fs_compat_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 update_inode_page(struct inode *);
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 25a1f7e..4b43b3f 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -580,7 +580,7 @@ next_step:
 		ofs_in_node = le16_to_cpu(entry->ofs_in_node);
 
 		if (phase == 2) {
-			inode = f2fs_iget(sb, dni.ino);
+			inode = f2fs_iget_nowait(sb, dni.ino);
 			if (IS_ERR(inode))
 				continue;
 
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 91ac7f9..a0879c3 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -18,6 +18,11 @@
 
 #include <trace/events/f2fs.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;
@@ -37,6 +42,34 @@ 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);
-- 
1.8.1.3.566.gaa39828