[PATCH] ext4: defend against inline-to-block conversion race in write completion

[Deepanshu Kartikey <kartikey406@gmail.com>]

Replace BUG_ON(!ext4_has_inline_data(inode)) with defensive error handling
in ext4_write_inline_data_end(). A file can be converted from inline to block
storage by concurrent paths while a write completion is in flight.

Lock-based synchronization is impractical here since multiple conversion paths
use different locks. Defensive check with proper cleanup
handles all races uniformly and safely.

Reported-by: syzbot+293a57918b36cfae3d48@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=293a57918b36cfae3d48
Tested-by: syzbot+293a57918b36cfae3d48@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/ext4/inline.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 8045e4ff270c..53d783235da9 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -812,7 +812,14 @@ int ext4_write_inline_data_end(struct inode *inode, loff_t pos, unsigned len,
 			goto out;
 		}
 		ext4_write_lock_xattr(inode, &no_expand);
-		BUG_ON(!ext4_has_inline_data(inode));
+		/* File may have been converted to block storage by concurrent path */
+		if (!ext4_has_inline_data(inode)) {
+			ext4_write_unlock_xattr(inode, &no_expand);
+			brelse(iloc.bh);
+			folio_unlock(folio);
+			folio_put(folio);
+			return -EIO;
+		}
 
 		/*
 		 * ei->i_inline_off may have changed since
-- 
2.43.0