Re: [PATCH 2/3] ext4: Do not create EA inode under buffer lock

["Theodore Ts'o" <tytso@mit.edu>]

On Fri, Feb 09, 2024 at 12:21:00PM +0100, Jan Kara wrote:
> ext4_xattr_set_entry() creates new EA inodes while holding buffer lock
> on the external xattr block. This is problematic as it nests all the
> allocation locking (which acquires locks on other buffers) under the
> buffer lock. This can even deadlock when the filesystem is corrupted and
> e.g. quota file is setup to contain xattr block as data block. Move the
> allocation of EA inode out of ext4_xattr_set_entry() into the callers.
> 
> Reported-by: syzbot+a43d4f48b8397d0e41a9@syzkaller.appspotmail.com
> Signed-off-by: Jan Kara <jack@suse.cz>

In my testing I've found that this is causing a regression for
ext4/026 in the encrypt configuration.  This can be replicated using
"kvm-xfstests -c encrypt ext4/026.   Logs follow below.

I'll try to take a closer look, but I may end up deciding to drop this
patch or possible the whole patch series until we can figure out
what's going on.

						- Ted

ext4/026 1s ...  [10:51:57][    3.111475] run fstests ext4/026 at 2024-02-29 10:51:57
EXT4-fs (vdc): Test dummy encryption mode enabled
EXT4-fs (vdc): Test dummy encryption mode enabled
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
------------[ cut here ]------------
EA inode 18 ref_count=-1
WARNING: CPU: 0 PID: 2391 at fs/ext4/xattr.c:1064 ext4_xattr_inode_update_ref+0x1c0/0x230
CPU: 0 PID: 2391 Comm: setfattr Not tainted 6.8.0-rc3-xfstests-00021-gf7528aea5d49 #320
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:ext4_xattr_inode_update_ref+0x1c0/0x230
Code: 0b e9 21 ff ff ff 80 3d 13 47 5a 01 00 0f 85 14 ff ff ff 48 8b 73 40 48 c7 c7 a6 8e 5d 82 c6 05 fb 46 5a 01 01 e8 50 40 c1 ff <0f> 0b e9 f6 fe ff ff 80 3d e7 46 5a 01 00 0f 85 5d ff ff ff 48 8b
RSP: 0018:ffffc900032cb980 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff8880043438a8 RCX: 0000000000000027
RDX: ffff88807dc1c848 RSI: 0000000000000001 RDI: ffff88807dc1c840
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff82860e00
R10: ffffc900032cb828 R11: ffffffff828d0e48 R12: ffff888007c93150
R13: ffff888004343948 R14: 00000000ffffffff R15: ffff8880043438a8
FS:  00007fab1e02b740(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055e0e4fd2000 CR3: 000000000a0a6002 CR4: 0000000000770ef0
PKRU: 55555554
Call Trace:
 <TASK>
 ? ext4_xattr_inode_update_ref+0x1c0/0x230
 ? __warn+0x7c/0x130
 ? ext4_xattr_inode_update_ref+0x1c0/0x230
 ? report_bug+0x173/0x1d0
 ? handle_bug+0x3a/0x70
 ? exc_invalid_op+0x17/0x70
 ? asm_exc_invalid_op+0x1a/0x20
 ? ext4_xattr_inode_update_ref+0x1c0/0x230
 ext4_xattr_inode_dec_ref_all+0x166/0x330
 ext4_xattr_release_block+0x29e/0x300
 ext4_xattr_block_set+0x795/0xc70
 ext4_xattr_set_handle+0x468/0x680
 ext4_xattr_set+0x88/0x160
 __vfs_setxattr+0x96/0xd0
 __vfs_setxattr_noperm+0x79/0x1d0
 vfs_setxattr+0x9f/0x180
 setxattr+0x9e/0xc0
 path_setxattr+0xc9/0xf0
 __x64_sys_setxattr+0x2b/0x40
 do_syscall_64+0x52/0x120
 entry_SYSCALL_64_after_hwframe+0x6e/0x76
RIP: 0033:0x7fab1e12f4f9
Code: 08 89 e8 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d d7 08 0d 00 f7 d8 64 89 01 48
RSP: 002b:00007fffe7694618 EFLAGS: 00000206 ORIG_RAX: 00000000000000bc
RAX: ffffffffffffffda RBX: 000055e0e4fc3340 RCX: 00007fab1e12f4f9
RDX: 000055e0e4fc3340 RSI: 00007fffe7695a22 RDI: 00007fffe76a5a96
RBP: 00007fffe76a5a96 R08: 0000000000000000 R09: 00007fab1e247020
R10: 0000000000010000 R11: 0000000000000206 R12: 00007fffe7695a22
R13: 000055e0e3e8008c R14: 000055e0e3e82100 R15: 00007fab1e247020
 </TASK>
---[ end trace 0000000000000000 ]---
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs error (device vdc): ext4_xattr_inode_iget:443: comm getfattr: error while reading EA inode 18 err=-116
EXT4-fs (vdc): Test dummy encryption mode enabled
EXT4-fs (vdc): warning: mounting fs with errors, running e2fsck is recommended