syzbot


possible deadlock in ext4_xattr_get (2)

Status: upstream: reported on 2025/11/08 13:32
Subsystems: ext4
[Documentation on labels]
Reported-by: syzbot+5b61c1d24f8022b26f7d@syzkaller.appspotmail.com
First crash: 50d, last: 20d
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [ext4?] possible deadlock in ext4_xattr_get (2) 0 (1) 2025/11/08 13:32
Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 possible deadlock in ext4_xattr_get 4 2 1d17h 39d 0/2 upstream: reported on 2025/11/14 21:22
linux-6.1 possible deadlock in ext4_xattr_get 4 1 13d 13d 0/3 upstream: reported on 2025/12/11 02:47
linux-4.14 possible deadlock in ext4_xattr_get 4 C inconclusive 1 1337d 1337d 0/1 upstream: reported C repro on 2022/04/27 03:33
linux-5.15 possible deadlock in ext4_xattr_get 4 2 2d08h 15d 0/3 upstream: reported on 2025/12/09 00:14
upstream possible deadlock in ext4_xattr_get ext4 4 C inconclusive 3 962d 1235d 22/29 fixed on 2023/07/01 16:05
linux-4.19 possible deadlock in ext4_xattr_get 4 C error 1 1337d 1337d 0/1 upstream: reported C repro on 2022/04/27 05:09

Sample crash report:
EXT4-fs (loop7): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
ext4 filesystem being mounted at /103/file1 supports timestamps until 2038-01-19 (0x7fffffff)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.7.2461/16085 is trying to acquire lock:
ffff888052ed2708 (&ei->xattr_sem){++++}-{4:4}, at: ext4_xattr_get+0x10a/0x6a0 fs/ext4/xattr.c:708

but task is already holding lock:
ffff888033ae6b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1808 [inline]
ffff888033ae6b98 (&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}:
       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:3020
       do_writepages+0x32e/0x550 mm/page-writeback.c:2598
       __writeback_single_inode+0x133/0x1240 fs/fs-writeback.c:1737
       writeback_single_inode+0x493/0xc70 fs/fs-writeback.c:1858
       write_inode_now+0x160/0x1d0 fs/fs-writeback.c:2924
       iput_final fs/inode.c:1941 [inline]
       iput+0xa77/0x1030 fs/inode.c:2003
       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:6360
       ext4_try_to_expand_extra_isize fs/ext4/inode.c:6403 [inline]
       __ext4_mark_inode_dirty+0x45c/0x6e0 fs/ext4/inode.c:6481
       ext4_evict_inode+0x79c/0xe60 fs/ext4/inode.c:253
       evict+0x5f4/0xae0 fs/inode.c:837
       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:1699
       vfs_get_tree+0x92/0x2a0 fs/super.c:1759
       fc_mount fs/namespace.c:1199 [inline]
       do_new_mount_fc fs/namespace.c:3636 [inline]
       do_new_mount+0x302/0xa10 fs/namespace.c:3712
       do_mount fs/namespace.c:4035 [inline]
       __do_sys_mount fs/namespace.c:4224 [inline]
       __se_sys_mount+0x313/0x410 fs/namespace.c:4201
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xf80 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 kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
       down_read+0x47/0x2e0 kernel/locking/rwsem.c:1537
       ext4_xattr_get+0x10a/0x6a0 fs/ext4/xattr.c:708
       ext4_get_acl+0x84/0x930 fs/ext4/acl.c:165
       __get_acl+0x279/0x400 fs/posix_acl.c:159
       get_inode_acl fs/posix_acl.c:184 [inline]
       posix_acl_create+0x134/0x4a0 fs/posix_acl.c:646
       ext4_init_acl+0xb3/0x320 fs/ext4/acl.c:284
       __ext4_new_inode+0x31fb/0x3c90 fs/ext4/ialloc.c:1321
       ext4_ext_migrate+0x69f/0x1010 fs/ext4/migrate.c:456
       __ext4_ioctl fs/ext4/ioctl.c:1694 [inline]
       ext4_ioctl+0x204b/0x48e0 fs/ext4/ioctl.c:1923
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xf80 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);
  rlock(&ei->xattr_sem);

 *** DEADLOCK ***

3 locks held by syz.7.2461/16085:
 #0: ffff888074f72420 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write_file+0x60/0x200 fs/namespace.c:543
 #1: ffff88806ba6ed10 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: inode_lock include/linux/fs.h:1027 [inline]
 #1: ffff88806ba6ed10 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: __ext4_ioctl fs/ext4/ioctl.c:1693 [inline]
 #1: ffff88806ba6ed10 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: ext4_ioctl+0x2043/0x48e0 fs/ext4/ioctl.c:1923
 #2: ffff888033ae6b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_write fs/ext4/ext4.h:1808 [inline]
 #2: ffff888033ae6b98 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_ext_migrate+0x2f3/0x1010 fs/ext4/migrate.c:438

stack backtrace:
CPU: 1 UID: 0 PID: 16085 Comm: syz.7.2461 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 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 kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868
 down_read+0x47/0x2e0 kernel/locking/rwsem.c:1537
 ext4_xattr_get+0x10a/0x6a0 fs/ext4/xattr.c:708
 ext4_get_acl+0x84/0x930 fs/ext4/acl.c:165
 __get_acl+0x279/0x400 fs/posix_acl.c:159
 get_inode_acl fs/posix_acl.c:184 [inline]
 posix_acl_create+0x134/0x4a0 fs/posix_acl.c:646
 ext4_init_acl+0xb3/0x320 fs/ext4/acl.c:284
 __ext4_new_inode+0x31fb/0x3c90 fs/ext4/ialloc.c:1321
 ext4_ext_migrate+0x69f/0x1010 fs/ext4/migrate.c:456
 __ext4_ioctl fs/ext4/ioctl.c:1694 [inline]
 ext4_ioctl+0x204b/0x48e0 fs/ext4/ioctl.c:1923
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f47b1f8f749
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:00007f47b2d48038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f47b21e5fa0 RCX: 00007f47b1f8f749
RDX: 0000000000000000 RSI: 0000000000006609 RDI: 0000000000000004
RBP: 00007f47b2013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f47b21e6038 R14: 00007f47b21e5fa0 R15: 00007ffc778bfb08
 </TASK>

Crashes (7):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/03 22:45 upstream 3f9f0252130e d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in ext4_xattr_get
2025/12/03 07:41 upstream d61f1cc5db79 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root possible deadlock in ext4_xattr_get
2025/12/03 01:03 upstream 4a26e7032d7d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in ext4_xattr_get
2025/12/02 15:59 upstream 4a26e7032d7d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root possible deadlock in ext4_xattr_get
2025/11/25 15:24 upstream ac3fd01e4c1e 64219f15 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in ext4_xattr_get
2025/11/04 13:30 upstream 8bb886cb8f3a 686bf657 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in ext4_xattr_get
2025/11/22 16:51 linux-next d724c6f85e80 4fb8ef37 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root possible deadlock in ext4_xattr_get
* Struck through repros no longer work on HEAD.