Re: [syzbot] [ext4?] possible deadlock in ext4_xattr_inode_iget

syzbot
2023-05-08T03:21:47Z

syzbot has found a reproducer for the following issue on:

HEAD commit: 83e5775d7afd Add linux-next specific files for 20230505
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=15a5bb4a280000
kernel config: https://syzkaller.appspot.com/x/.config?x=d0c6b4b7069d73cf
dashboard link: https://syzkaller.appspot.com/bug?extid=298c5d8fb4a128bc27b0
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17b7c75c280000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1284b832280000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/95513581563c/disk-83e5775d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a4e06ec61bde/vmlinux-83e5775d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ccebc2ffc0a5/bzImage-83e5775d.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/2abf046bc472/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+298c5d8fb4a128bc27b0@syzkaller.appspotmail.com

EXT4-fs (loop0): 1 truncate cleaned up
EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 without journal. Quota mode: writeback.
======================================================
WARNING: possible circular locking dependency detected
6.3.0-next-20230505-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor168/5006 is trying to acquire lock:
ffff888077185e00 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:775 [inline]
ffff888077185e00 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}, at: ext4_xattr_inode_iget+0x2b8/0x660 fs/ext4/xattr.c:474

but task is already holding lock:
ffff888077185288 (&ei->i_data_sem){++++}-{3:3}, at: ext4_setattr+0x1925/0x26c0 fs/ext4/inode.c:5397

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&ei->i_data_sem){++++}-{3:3}:
down_write+0x92/0x200 kernel/locking/rwsem.c:1573
ext4_update_i_disksize fs/ext4/ext4.h:3293 [inline]
ext4_xattr_inode_write fs/ext4/xattr.c:1462 [inline]
ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1611 [inline]
ext4_xattr_set_entry+0x30c5/0x39e0 fs/ext4/xattr.c:1736
ext4_xattr_ibody_set+0x131/0x3a0 fs/ext4/xattr.c:2288
ext4_xattr_set_handle+0x968/0x1510 fs/ext4/xattr.c:2445
ext4_xattr_set+0x144/0x360 fs/ext4/xattr.c:2559
__vfs_setxattr+0x173/0x1e0 fs/xattr.c:201
__vfs_setxattr_noperm+0x129/0x5f0 fs/xattr.c:235
__vfs_setxattr_locked+0x1d3/0x260 fs/xattr.c:296
vfs_setxattr+0x143/0x340 fs/xattr.c:322
do_setxattr+0x147/0x190 fs/xattr.c:630
setxattr+0x146/0x160 fs/xattr.c:653
path_setxattr+0x197/0x1c0 fs/xattr.c:672
__do_sys_setxattr fs/xattr.c:688 [inline]
__se_sys_setxattr fs/xattr.c:684 [inline]
__x64_sys_setxattr+0xc4/0x160 fs/xattr.c:684
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

-> #0 (&ea_inode->i_rwsem#8/1){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3113 [inline]
check_prevs_add kernel/locking/lockdep.c:3232 [inline]
validate_chain kernel/locking/lockdep.c:3847 [inline]
__lock_acquire+0x2fcd/0x5f30 kernel/locking/lockdep.c:5088
lock_acquire.part.0+0x11c/0x370 kernel/locking/lockdep.c:5705
down_write+0x92/0x200 kernel/locking/rwsem.c:1573
inode_lock include/linux/fs.h:775 [inline]
ext4_xattr_inode_iget+0x2b8/0x660 fs/ext4/xattr.c:474
ext4_xattr_inode_get+0x162/0x830 fs/ext4/xattr.c:551
ext4_xattr_move_to_block fs/ext4/xattr.c:2640 [inline]
ext4_xattr_make_inode_space fs/ext4/xattr.c:2742 [inline]
ext4_expand_extra_isize_ea+0xf6d/0x1880 fs/ext4/xattr.c:2834
__ext4_expand_extra_isize+0x33e/0x470 fs/ext4/inode.c:5769
ext4_try_to_expand_extra_isize fs/ext4/inode.c:5812 [inline]
__ext4_mark_inode_dirty+0x51b/0x800 fs/ext4/inode.c:5890
ext4_setattr+0x199f/0x26c0 fs/ext4/inode.c:5400
notify_change+0xb2c/0x1180 fs/attr.c:483
do_truncate+0x143/0x200 fs/open.c:66
handle_truncate fs/namei.c:3295 [inline]
do_open fs/namei.c:3640 [inline]
path_openat+0x2083/0x2750 fs/namei.c:3791
do_filp_open+0x1ba/0x410 fs/namei.c:3818
do_sys_openat2+0x16d/0x4c0 fs/open.c:1356
do_sys_open fs/open.c:1372 [inline]
__do_sys_creat fs/open.c:1448 [inline]
__se_sys_creat fs/open.c:1442 [inline]
__x64_sys_creat+0xcd/0x120 fs/open.c:1442
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&ei->i_data_sem);
lock(&ea_inode->i_rwsem#8/1);
lock(&ei->i_data_sem);
lock(&ea_inode->i_rwsem#8/1);

*** DEADLOCK ***

5 locks held by syz-executor168/5006:
#0: ffff88801a7b4460 (sb_writers#4){.+.+}-{0:0}, at: do_open fs/namei.c:3629 [inline]
#0: ffff88801a7b4460 (sb_writers#4){.+.+}-{0:0}, at: path_openat+0x19a4/0x2750 fs/namei.c:3791
#1: ffff888077185400 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: inode_lock include/linux/fs.h:775 [inline]
#1: ffff888077185400 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: do_truncate+0x131/0x200 fs/open.c:64
#2: ffff8880771855a0 (mapping.invalidate_lock){++++}-{3:3}, at: filemap_invalidate_lock include/linux/fs.h:820 [inline]
#2: ffff8880771855a0 (mapping.invalidate_lock){++++}-{3:3}, at: ext4_setattr+0x68f/0x26c0 fs/ext4/inode.c:5357
#3: ffff888077185288 (&ei->i_data_sem){++++}-{3:3}, at: ext4_setattr+0x1925/0x26c0 fs/ext4/inode.c:5397
#4: ffff8880771850c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_trylock_xattr fs/ext4/xattr.h:162 [inline]
#4: ffff8880771850c8 (&ei->xattr_sem){++++}-{3:3}, at: ext4_try_to_expand_extra_isize fs/ext4/inode.c:5809 [inline]
#4: ffff8880771850c8 (&ei->xattr_sem){++++}-{3:3}, at: __ext4_mark_inode_dirty+0x48f/0x800 fs/ext4/inode.c:5890

stack backtrace:
CPU: 0 PID: 5006 Comm: syz-executor168 Not tainted 6.3.0-next-20230505-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2188
check_prev_add kernel/locking/lockdep.c:3113 [inline]
check_prevs_add kernel/locking/lockdep.c:3232 [inline]
validate_chain kernel/locking/lockdep.c:3847 [inline]
__lock_acquire+0x2fcd/0x5f30 kernel/locking/lockdep.c:5088
lock_acquire.part.0+0x11c/0x370 kernel/locking/lockdep.c:5705
down_write+0x92/0x200 kernel/locking/rwsem.c:1573
inode_lock include/linux/fs.h:775 [inline]
ext4_xattr_inode_iget+0x2b8/0x660 fs/ext4/xattr.c:474
ext4_xattr_inode_get+0x162/0x830 fs/ext4/xattr.c:551
ext4_xattr_move_to_block fs/ext4/xattr.c:2640 [inline]
ext4_xattr_make_inode_space fs/ext4/xattr.c:2742 [inline]
ext4_expand_extra_isize_ea+0xf6d/0x1880 fs/ext4/xattr.c:2834
__ext4_expand_extra_isize+0x33e/0x470 fs/ext4/inode.c:5769
ext4_try_to_expand_extra_isize fs/ext4/inode.c:5812 [inline]
__ext4_mark_inode_dirty+0x51b/0x800 fs/ext4/inode.c:5890
ext4_setattr+0x199f/0x26c0 fs/ext4/inode.c:5400
notify_change+0xb2c/0x1180 fs/attr.c:483
do_truncate+0x143/0x200 fs/open.c:66
handle_truncate fs/namei.c:3295 [inline]
do_open fs/namei.c:3640 [inline]
path_openat+0x2083/0x2750 fs/namei.c:3791
do_filp_open+0x1ba/0x410 fs/namei.c:3818
do_sys_openat2+0x16d/0x4c0 fs/open.c:1356
do_sys_open fs/open.c:1372 [inline]
__do_sys_creat fs/open.c:1448 [inline]
__se_sys_creat fs/open.c:1442 [inline]
__x64_sys_creat+0xcd/0x120 fs/open.c:1442
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7efc2e57ac09
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 14 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 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd62b7d568 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 0031656c69662f2e RCX: 00007efc2e57ac09
RDX: 00007efc2e57ac09 RSI: 0000000000000000 RDI: 0000000020000400
RBP: 00007efc2e53a210 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0

---
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