f2fs: avoid deadlock during evict after f2fs_gc

o Deadlock case #1

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

o Deadlock case #2

Thread 1:
- __writeback_single_inode
 : set I_SYNC
  - do_writepages
   - f2fs_write_data_page
    - f2fs_balance_fs
     - f2fs_gc
      - iput
       - evict
        - inode_wait_for_writeback(I_SYNC)

In order to avoid this, even though iput is called with the zero-reference
count, we need to stop the eviction procedure if the inode is on writeback.
So this patch links f2fs_drop_inode which checks the I_SYNC flag.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/data.c

@@ -577,6 +577,7 @@ static int f2fs_write_data_pages(struct address_space *mapping,
 {
 	struct inode *inode = mapping->host;
 	struct f2fs_sb_info *sbi = F2FS_SB(inode->i_sb);
+	bool locked = false;
 	int ret;
 	long excess_nrtw = 0, desired_nrtw;
 
@@ -590,10 +591,12 @@ static int f2fs_write_data_pages(struct address_space *mapping,
 		wbc->nr_to_write = desired_nrtw;
 	}
 
-	if (!S_ISDIR(inode->i_mode))
+	if (!S_ISDIR(inode->i_mode)) {
 		mutex_lock(&sbi->writepages);
+		locked = true;
+	}
 	ret = write_cache_pages(mapping, wbc, __f2fs_writepage, mapping);
-	if (!S_ISDIR(inode->i_mode))
+	if (locked)
 		mutex_unlock(&sbi->writepages);
 	f2fs_submit_bio(sbi, DATA, (wbc->sync_mode == WB_SYNC_ALL));
 

fs/f2fs/namei.c

@@ -72,6 +72,7 @@ static struct inode *f2fs_new_inode(struct inode *dir, umode_t mode)
 	unlock_new_inode(inode);
 fail:
 	trace_f2fs_new_inode(inode, err);
+	make_bad_inode(inode);
 	iput(inode);
 	if (nid_free)
 		alloc_nid_failed(sbi, ino);
@@ -155,6 +156,7 @@ static int f2fs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
 out:
 	clear_nlink(inode);
 	unlock_new_inode(inode);
+	make_bad_inode(inode);
 	iput(inode);
 	alloc_nid_failed(sbi, ino);
 	return err;
@@ -190,6 +192,7 @@ static int f2fs_link(struct dentry *old_dentry, struct inode *dir,
 	return 0;
 out:
 	clear_inode_flag(F2FS_I(inode), FI_INC_LINK);
+	make_bad_inode(inode);
 	iput(inode);
 	return err;
 }
@@ -295,6 +298,7 @@ static int f2fs_symlink(struct inode *dir, struct dentry *dentry,
 out:
 	clear_nlink(inode);
 	unlock_new_inode(inode);
+	make_bad_inode(inode);
 	iput(inode);
 	alloc_nid_failed(sbi, inode->i_ino);
 	return err;
@@ -335,6 +339,7 @@ static int f2fs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
 	clear_inode_flag(F2FS_I(inode), FI_INC_LINK);
 	clear_nlink(inode);
 	unlock_new_inode(inode);
+	make_bad_inode(inode);
 	iput(inode);
 	alloc_nid_failed(sbi, inode->i_ino);
 	return err;
@@ -382,6 +387,7 @@ static int f2fs_mknod(struct inode *dir, struct dentry *dentry,
 out:
 	clear_nlink(inode);
 	unlock_new_inode(inode);
+	make_bad_inode(inode);
 	iput(inode);
 	alloc_nid_failed(sbi, inode->i_ino);
 	return err;

fs/f2fs/super.c

@@ -98,6 +98,20 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
 	return &fi->vfs_inode;
 }
 
+static int f2fs_drop_inode(struct inode *inode)
+{
+	/*
+	 * This is to avoid a deadlock condition like below.
+	 * writeback_single_inode(inode)
+	 *  - f2fs_write_data_page
+	 *    - f2fs_gc -> iput -> evict
+	 *       - inode_wait_for_writeback(inode)
+	 */
+	if (!inode_unhashed(inode) && inode->i_state & I_SYNC)
+		return 0;
+	return generic_drop_inode(inode);
+}
+
 static void f2fs_i_callback(struct rcu_head *head)
 {
 	struct inode *inode = container_of(head, struct inode, i_rcu);
@@ -232,6 +246,7 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 
 static struct super_operations f2fs_sops = {
 	.alloc_inode	= f2fs_alloc_inode,
+	.drop_inode	= f2fs_drop_inode,
 	.destroy_inode	= f2fs_destroy_inode,
 	.write_inode	= f2fs_write_inode,
 	.show_options	= f2fs_show_options,