linux-kernel - Re: [syzbot] [ext4?] possible deadlock in ext4_xattr_inode

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Date: Wed,  3 Apr 2024 21:44:54 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+ee72b9a7aad1e5a77c5c@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [ext4?] possible deadlock in ext4_xattr_inode_iget (3)

On Wed, 03 Apr 2024 00:45:29 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    fe46a7dd189e Merge tag 'sound-6.9-rc1' of git://git.kernel..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=140d9db1180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  fe46a7dd189e

--- x/fs/ext4/inode.c
+++ y/fs/ext4/inode.c
@@ -5414,6 +5414,7 @@ int ext4_setattr(struct mnt_idmap *idmap
 					(attr->ia_size > 0 ? attr->ia_size - 1 : 0) >>
 					inode->i_sb->s_blocksize_bits);
 
+			down_read(&EXT4_I(inode)->xattr_sem);
 			down_write(&EXT4_I(inode)->i_data_sem);
 			old_disksize = EXT4_I(inode)->i_disksize;
 			EXT4_I(inode)->i_disksize = attr->ia_size;
@@ -5430,6 +5431,7 @@ int ext4_setattr(struct mnt_idmap *idmap
 			else
 				EXT4_I(inode)->i_disksize = old_disksize;
 			up_write(&EXT4_I(inode)->i_data_sem);
+			up_read(&EXT4_I(inode)->xattr_sem);
 			ext4_journal_stop(handle);
 			if (error)
 				goto out_mmap_sem;
--