syzbot


possible deadlock in ext4_xattr_set_handle (7)

Status: upstream: reported on 2025/11/13 08:08
Subsystems: ext4
[Documentation on labels]
Reported-by: syzbot+f0b58a1f5075a90dd9a5@syzkaller.appspotmail.com
First crash: 5d08h, last: 5d08h
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [ext4?] possible deadlock in ext4_xattr_set_handle (7) 0 (1) 2025/11/13 08:08
Similar bugs (9)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream possible deadlock in ext4_xattr_set_handle (5) ext4 4 72 506d 550d 0/29 auto-obsoleted due to no activity on 2024/09/03 19:27
upstream possible deadlock in ext4_xattr_set_handle (3) ext4 4 C 451 867d 1024d 22/29 fixed on 2023/07/01 16:05
upstream possible deadlock in ext4_xattr_set_handle (4) ext4 4 5 664d 784d 0/29 auto-obsoleted due to no activity on 2024/04/29 16:11
upstream possible deadlock in ext4_xattr_set_handle ext4 4 1 1487d 1483d 0/29 auto-closed as invalid on 2022/02/15 19:59
upstream possible deadlock in ext4_xattr_set_handle (6) ext4 4 50 387d 408d 0/29 auto-obsoleted due to no activity on 2025/01/01 12:48
upstream possible deadlock in ext4_xattr_set_handle (2) ext4 4 1 1222d 1221d 0/29 auto-obsoleted due to no activity on 2022/11/08 16:24
linux-5.15 possible deadlock in ext4_xattr_set_handle 4 C done 42 890d 982d 3/3 fixed on 2023/07/17 13:09
linux-4.19 possible deadlock in ext4_xattr_set_handle ext4 4 1 1015d 1015d 0/1 upstream: reported on 2023/02/03 16:43
linux-6.1 possible deadlock in ext4_xattr_set_handle 4 C done 15 890d 978d 3/3 fixed on 2023/07/17 13:09

Sample crash report:
EXT4-fs (loop8): mounted filesystem 76b65be2-f6da-4727-8c75-0525a5b65a09 r/w without journal. Quota mode: none.
ext4 filesystem being mounted at /81/mnt supports timestamps until 2038-01-19 (0x7fffffff)
fscrypt: AES-256-XTS using implementation "xts-aes-vaes-avx2"
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.8.1928/14101 is trying to acquire lock:
ffff8880494b9d78 (&ei->xattr_sem){++++}-{4:4}, at: ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
ffff8880494b9d78 (&ei->xattr_sem){++++}-{4:4}, at: ext4_xattr_set_handle+0x165/0x1590 fs/ext4/xattr.c:2367

but task is already holding lock:
ffff888031d78b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1808 [inline]
ffff888031d78b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_ext_migrate+0x2f3/0x1010 fs/ext4/migrate.c:438

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&sbi->s_writepages_rwsem){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       percpu_down_read_internal+0x48/0x1c0 include/linux/percpu-rwsem.h:53
       percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
       ext4_writepages_down_read fs/ext4/ext4.h:1796 [inline]
       ext4_writepages+0x1cc/0x350 fs/ext4/inode.c:3024
       do_writepages+0x32e/0x550 mm/page-writeback.c:2604
       __writeback_single_inode+0x145/0xff0 fs/fs-writeback.c:1719
       writeback_single_inode+0x1f9/0x6a0 fs/fs-writeback.c:1840
       write_inode_now+0x160/0x1d0 fs/fs-writeback.c:2903
       iput_final fs/inode.c:1901 [inline]
       iput+0x830/0xc50 fs/inode.c:1966
       ext4_xattr_block_set+0x1fce/0x2ac0 fs/ext4/xattr.c:2199
       ext4_xattr_move_to_block fs/ext4/xattr.c:2664 [inline]
       ext4_xattr_make_inode_space fs/ext4/xattr.c:2739 [inline]
       ext4_expand_extra_isize_ea+0x12da/0x1ea0 fs/ext4/xattr.c:2827
       __ext4_expand_extra_isize+0x30d/0x400 fs/ext4/inode.c:6364
       ext4_try_to_expand_extra_isize fs/ext4/inode.c:6407 [inline]
       __ext4_mark_inode_dirty+0x46c/0x700 fs/ext4/inode.c:6485
       ext4_evict_inode+0x80d/0xee0 fs/ext4/inode.c:254
       evict+0x504/0x9c0 fs/inode.c:810
       ext4_orphan_cleanup+0xc20/0x1460 fs/ext4/orphan.c:470
       __ext4_fill_super fs/ext4/super.c:5617 [inline]
       ext4_fill_super+0x5920/0x61e0 fs/ext4/super.c:5736
       get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
       vfs_get_tree+0x92/0x2b0 fs/super.c:1751
       fc_mount fs/namespace.c:1208 [inline]
       do_new_mount_fc fs/namespace.c:3651 [inline]
       do_new_mount+0x302/0xa10 fs/namespace.c:3727
       do_mount fs/namespace.c:4050 [inline]
       __do_sys_mount fs/namespace.c:4238 [inline]
       __se_sys_mount+0x313/0x410 fs/namespace.c:4215
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&ei->xattr_sem){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590
       ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
       ext4_xattr_set_handle+0x165/0x1590 fs/ext4/xattr.c:2367
       ext4_set_context+0x21b/0x550 fs/ext4/crypto.c:166
       fscrypt_set_context+0x38a/0x460 fs/crypto/policy.c:791
       __ext4_new_inode+0x3143/0x3cb0 fs/ext4/ialloc.c:1315
       ext4_ext_migrate+0x69f/0x1010 fs/ext4/migrate.c:456
       ext4_ioctl_setflags fs/ext4/ioctl.c:705 [inline]
       ext4_fileattr_set+0xeaf/0x1630 fs/ext4/ioctl.c:1024
       vfs_fileattr_set+0x932/0xb90 fs/file_attr.c:298
       ioctl_setflags+0x180/0x1e0 fs/file_attr.c:334
       do_vfs_ioctl+0x8ed/0x1430 fs/ioctl.c:560
       __do_sys_ioctl fs/ioctl.c:595 [inline]
       __se_sys_ioctl+0x82/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sbi->s_writepages_rwsem);
                               lock(&ei->xattr_sem);
                               lock(&sbi->s_writepages_rwsem);
  lock(&ei->xattr_sem);

 *** DEADLOCK ***

3 locks held by syz.8.1928/14101:
 #0: ffff888031d7e420 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200 fs/namespace.c:552
 #1: ffff8880494bd9f0 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: inode_lock include/linux/fs.h:980 [inline]
 #1: ffff8880494bd9f0 (&type->i_mutex_dir_key#3){++++}-{4:4}, at: vfs_fileattr_set+0x14e/0xb90 fs/file_attr.c:278
 #2: ffff888031d78b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1808 [inline]
 #2: ffff888031d78b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_ext_migrate+0x2f3/0x1010 fs/ext4/migrate.c:438

stack backtrace:
CPU: 0 UID: 0 PID: 14101 Comm: syz.8.1928 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 down_write+0x96/0x1f0 kernel/locking/rwsem.c:1590
 ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
 ext4_xattr_set_handle+0x165/0x1590 fs/ext4/xattr.c:2367
 ext4_set_context+0x21b/0x550 fs/ext4/crypto.c:166
 fscrypt_set_context+0x38a/0x460 fs/crypto/policy.c:791
 __ext4_new_inode+0x3143/0x3cb0 fs/ext4/ialloc.c:1315
 ext4_ext_migrate+0x69f/0x1010 fs/ext4/migrate.c:456
 ext4_ioctl_setflags fs/ext4/ioctl.c:705 [inline]
 ext4_fileattr_set+0xeaf/0x1630 fs/ext4/ioctl.c:1024
 vfs_fileattr_set+0x932/0xb90 fs/file_attr.c:298
 ioctl_setflags+0x180/0x1e0 fs/file_attr.c:334
 do_vfs_ioctl+0x8ed/0x1430 fs/ioctl.c:560
 __do_sys_ioctl fs/ioctl.c:595 [inline]
 __se_sys_ioctl+0x82/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1f39f8f6c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1f3ade0038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f1f3a1e5fa0 RCX: 00007f1f39f8f6c9
RDX: 0000200000000080 RSI: 0000000040086602 RDI: 0000000000000004
RBP: 00007f1f3a011f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1f3a1e6038 R14: 00007f1f3a1e5fa0 R15: 00007fffb7f49f38
 </TASK>
EXT4-fs error (device loop8): ext4_validate_block_bitmap:423: comm syz.8.1928: bg 0: bad block bitmap checksum

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/09 08:02 upstream 7bb4d6512545 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in ext4_xattr_set_handle
2025/11/09 08:02 upstream 7bb4d6512545 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in ext4_xattr_set_handle
* Struck through repros no longer work on HEAD.