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Subject: Re: [syzbot] [f2fs?] kernel BUG in clear_inode (5)
Author: kth5965@gmail.com

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 786262be6048deab760f68c8acc2c85607165894

Please test the following root-cause fix against the latest upstream tree.

diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
index aec06fb4fd76..4047e446ca1d 100644
--- a/fs/f2fs/inline.c
+++ b/fs/f2fs/inline.c
@@ -55,7 +55,7 @@ bool f2fs_sanity_check_inline_data(struct inode *inode, struct folio *ifolio)
 		return false;
 
 	if (inode_has_blocks(inode, ifolio))
-		return false;
+		return !f2fs_exist_data(inode);
 
 	if (!support_inline_data(inode))
 		return true;
@@ -221,7 +221,7 @@ int f2fs_convert_inline_inode(struct inode *inode)
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct dnode_of_data dn;
 	struct f2fs_lock_context lc;
-	struct folio *ifolio, *folio;
+	struct folio *ifolio, *folio = NULL;
 	int err = 0;
 
 	if (f2fs_hw_is_readonly(sbi) || f2fs_readonly(sbi->sb))
@@ -234,10 +234,7 @@ int f2fs_convert_inline_inode(struct inode *inode)
 	if (err)
 		return err;
 
-	folio = f2fs_grab_cache_folio(inode->i_mapping, 0, false);
-	if (IS_ERR(folio))
-		return PTR_ERR(folio);
-
+retry:
 	f2fs_lock_op(sbi, &lc);
 
 	ifolio = f2fs_get_inode_folio(sbi, inode->i_ino);
@@ -248,6 +245,21 @@ int f2fs_convert_inline_inode(struct inode *inode)
 
 	set_new_dnode(&dn, inode, ifolio, ifolio, 0);
 
+	/*
+	 * Keep the folio #0 -> inode folio lock order while checking
+	 * FI_DATA_EXIST under the inode folio lock.
+	 */
+	if (!folio && f2fs_has_inline_data(inode) && f2fs_exist_data(inode)) {
+		f2fs_put_dnode(&dn);
+		f2fs_unlock_op(sbi, &lc);
+
+		folio = f2fs_grab_cache_folio(inode->i_mapping, 0, false);
+		if (IS_ERR(folio))
+			return PTR_ERR(folio);
+
+		goto retry;
+	}
+
 	if (f2fs_has_inline_data(inode))
 		err = f2fs_convert_inline_folio(&dn, folio);