syzbot

 sign-in | mailing list | source | docs
🐞 Open [815]
🐞 Fixed [85]
🐞 Invalid [1149]
⬇ Missing Backports [133]
≡ Crashes
Kernel Health Bugs/Month Bug Lifetimes Fuzzing
💬 Send us feedback

possible deadlock in ext4_move_extents (5)

Status: upstream: reported on 2025/10/27 19:09
Reported-by: syzbot+5cbbe39beb13abc8459b@syzkaller.appspotmail.com
First crash: 48d, last: 46d
▶ ▼ Similar bugs (8)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 possible deadlock in ext4_move_extents 4 2 864d 953d 0/3 auto-obsoleted due to no activity on 2023/11/11 09:48
linux-6.1 possible deadlock in ext4_move_extents (3) 4 20 34d 415d 0/3 upstream: reported on 2024/10/24 22:08
upstream possible deadlock in ext4_move_extents ext4 4 133 965d 1135d 0/29 auto-obsoleted due to no activity on 2023/08/22 15:17
linux-6.1 possible deadlock in ext4_move_extents (2) 4 6 552d 731d 0/3 auto-obsoleted due to no activity on 2024/09/18 11:30
linux-5.15 possible deadlock in ext4_move_extents 4 3 889d 965d 0/3 auto-obsoleted due to no activity on 2023/10/16 22:21
linux-5.15 possible deadlock in ext4_move_extents (2) 4 2 692d 761d 0/3 auto-obsoleted due to no activity on 2024/05/01 17:40
linux-5.15 possible deadlock in ext4_move_extents (3) 4 5 436d 565d 0/3 auto-obsoleted due to no activity on 2025/01/12 16:14
linux-5.15 possible deadlock in ext4_move_extents (4) 4 9 148d 316d 0/3 auto-obsoleted due to no activity on 2025/10/27 18:06

Sample crash report:
ext4 filesystem being mounted at /33/bus supports timestamps until 2038-01-19 (0x7fffffff)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.3.1360/9485 is trying to acquire lock:
ffff88805a65d238 (&ei->i_data_sem/1){+.+.}-{3:3}, at: ext4_move_extents+0x31e/0xbd0 fs/ext4/move_extent.c:609

but task is already holding lock:
ffff88805a65aa58 (&ei->i_data_sem/2){++++}-{3:3}, at: ext4_double_down_write_data_sem+0x28/0x40 fs/ext4/move_extent.c:-1

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&ei->i_data_sem/2){++++}-{3:3}:
       down_read+0x44/0x2e0 kernel/locking/rwsem.c:1498
       ext4_map_blocks+0x32f/0x1b30 fs/ext4/inode.c:598
       ext4_getblk+0x16d/0x630 fs/ext4/inode.c:870
       ext4_bread+0x26/0x180 fs/ext4/inode.c:923
       ext4_quota_read+0x1b3/0x3a0 fs/ext4/super.c:6550
       read_blk fs/quota/quota_tree.c:55 [inline]
       find_tree_dqentry+0x188/0xb30 fs/quota/quota_tree.c:617
       find_tree_dqentry+0x3eb/0xb30 fs/quota/quota_tree.c:635
       find_tree_dqentry+0x3eb/0xb30 fs/quota/quota_tree.c:635
       find_tree_dqentry+0x3eb/0xb30 fs/quota/quota_tree.c:635
       find_dqentry fs/quota/quota_tree.c:647 [inline]
       qtree_read_dquot+0x13c/0x680 fs/quota/quota_tree.c:667
       v2_read_dquot+0xc0/0x110 fs/quota/quota_v2.c:333
       dquot_acquire+0x152/0x520 fs/quota/dquot.c:463
       ext4_acquire_dquot+0x2d9/0x4a0 fs/ext4/super.c:6205
       dqget+0x778/0xeb0 fs/quota/dquot.c:988
       __dquot_initialize+0x328/0xcb0 fs/quota/dquot.c:1517
       ext4_process_orphan+0x54/0x300 fs/ext4/orphan.c:325
       ext4_orphan_cleanup+0xaa9/0x12e0 fs/ext4/orphan.c:470
       ext4_fill_super+0x92f0/0x9a60 fs/ext4/super.c:4975
       mount_bdev+0x287/0x3c0 fs/super.c:1400
       legacy_get_tree+0xe6/0x180 fs/fs_context.c:611
       vfs_get_tree+0x88/0x270 fs/super.c:1530
       do_new_mount+0x24a/0xa40 fs/namespace.c:3034
       do_mount fs/namespace.c:3377 [inline]
       __do_sys_mount fs/namespace.c:3585 [inline]
       __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:3562
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #2 (&s->s_dquot.dqio_sem){++++}-{3:3}:
       down_read+0x44/0x2e0 kernel/locking/rwsem.c:1498
       v2_read_dquot+0x4a/0x110 fs/quota/quota_v2.c:332
       dquot_acquire+0x152/0x520 fs/quota/dquot.c:463
       ext4_acquire_dquot+0x2d9/0x4a0 fs/ext4/super.c:6205
       dqget+0x778/0xeb0 fs/quota/dquot.c:988
       __dquot_initialize+0x3b6/0xcb0 fs/quota/dquot.c:1517
       add_dquot_ref+0x2b4/0x380 fs/quota/dquot.c:1060
       dquot_load_quota_sb+0x875/0xac0 fs/quota/dquot.c:2475
       dquot_resume+0x124/0x860 fs/quota/dquot.c:2532
       ext4_remount+0x1975/0x2690 fs/ext4/super.c:5993
       reconfigure_super+0x219/0x880 fs/super.c:938
       vfs_fsconfig_locked+0x18d/0x3f0 fs/fsopen.c:260
       __do_sys_fsconfig fs/fsopen.c:445 [inline]
       __se_sys_fsconfig+0x61b/0x750 fs/fsopen.c:320
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (&dquot->dq_lock){+.+.}-{3:3}:
       __mutex_lock_common+0x1eb/0x2390 kernel/locking/mutex.c:596
       __mutex_lock kernel/locking/mutex.c:729 [inline]
       mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
       dquot_commit+0x5a/0x410 fs/quota/dquot.c:507
       ext4_write_dquot+0x1f0/0x360 fs/ext4/super.c:6185
       mark_dquot_dirty fs/quota/dquot.c:372 [inline]
       mark_all_dquot_dirty+0x1e3/0x400 fs/quota/dquot.c:412
       __dquot_alloc_space+0x5d0/0xe20 fs/quota/dquot.c:1752
       dquot_alloc_space_nodirty include/linux/quotaops.h:297 [inline]
       dquot_alloc_space include/linux/quotaops.h:310 [inline]
       dquot_alloc_block include/linux/quotaops.h:334 [inline]
       ext4_mb_new_blocks+0xf68/0x4940 fs/ext4/mballoc.c:5734
       ext4_new_meta_blocks+0x151/0x3a0 fs/ext4/balloc.c:738
       ext4_ext_grow_indepth fs/ext4/extents.c:1325 [inline]
       ext4_ext_create_new_leaf fs/ext4/extents.c:1431 [inline]
       ext4_ext_insert_extent+0x1075/0x47e0 fs/ext4/extents.c:2103
       ext4_split_extent_at+0x76d/0xe50 fs/ext4/extents.c:3235
       ext4_force_split_extent_at fs/ext4/extents.c:319 [inline]
       ext4_swap_extents+0x10d2/0x1c20 fs/ext4/extents.c:5782
       move_extent_per_page+0x17c5/0x2e10 fs/ext4/move_extent.c:359
       ext4_move_extents+0x8b4/0xbd0 fs/ext4/move_extent.c:673
       __ext4_ioctl fs/ext4/ioctl.c:990 [inline]
       ext4_ioctl+0x2ce3/0x3590 fs/ext4/ioctl.c:1282
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #0 (&ei->i_data_sem/1){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
       lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
       down_write_nested+0x3b/0x60 kernel/locking/rwsem.c:1667
       ext4_move_extents+0x31e/0xbd0 fs/ext4/move_extent.c:609
       __ext4_ioctl fs/ext4/ioctl.c:990 [inline]
       ext4_ioctl+0x2ce3/0x3590 fs/ext4/ioctl.c:1282
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

other info that might help us debug this:

Chain exists of:
  &ei->i_data_sem/1 --> &s->s_dquot.dqio_sem --> &ei->i_data_sem/2

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ei->i_data_sem/2);
                               lock(&s->s_dquot.dqio_sem);
                               lock(&ei->i_data_sem/2);
  lock(&ei->i_data_sem/1);

 *** DEADLOCK ***

4 locks held by syz.3.1360/9485:
 #0: ffff88807b1a0460 (sb_writers#5){.+.+}-{0:0}, at: mnt_want_write_file+0x5c/0x200 fs/namespace.c:430
 #1: ffff88805a65abd0 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: inode_lock include/linux/fs.h:787 [inline]
 #1: ffff88805a65abd0 (&sb->s_type->i_mutex_key#9){++++}-{3:3}, at: lock_two_nondirectories+0xd5/0x150 fs/inode.c:1147
 #2: ffff88805a65d3b0 (&sb->s_type->i_mutex_key#9/4){+.+.}-{3:3}, at: ext4_move_extents+0x303/0xbd0 fs/ext4/move_extent.c:602
 #3: ffff88805a65aa58 (&ei->i_data_sem/2){++++}-{3:3}, at: ext4_double_down_write_data_sem+0x28/0x40 fs/ext4/move_extent.c:-1

stack backtrace:
CPU: 0 PID: 9485 Comm: syz.3.1360 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 check_noncircular+0x274/0x310 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x2c33/0x7c60 kernel/locking/lockdep.c:5012
 lock_acquire+0x197/0x3f0 kernel/locking/lockdep.c:5623
 down_write_nested+0x3b/0x60 kernel/locking/rwsem.c:1667
 ext4_move_extents+0x31e/0xbd0 fs/ext4/move_extent.c:609
 __ext4_ioctl fs/ext4/ioctl.c:990 [inline]
 ext4_ioctl+0x2ce3/0x3590 fs/ext4/ioctl.c:1282
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fbec35fdfc9
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:00007fbec1865038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fbec3854fa0 RCX: 00007fbec35fdfc9
RDX: 0000200000000040 RSI: 00000000c028660f RDI: 0000000000000005
RBP: 00007fbec3680f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbec3855038 R14: 00007fbec3854fa0 R15: 00007ffcb9c0b238
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/29 18:46 linux-5.15.y cc5ec8769306 fd2207e7 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in ext4_move_extents
2025/10/27 19:08 linux-5.15.y ac56c046adf4 fd2207e7 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan possible deadlock in ext4_move_extents
* Struck through repros no longer work on HEAD.