possible deadlock in v2_write_dquot

Status: upstream: reported on 2026/10/22 22:33
Subsystems: fs
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+75d986c18cef4710fc85@syzkaller.appspotmail.com
First crash: 4d07h, last: 4d07h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
04b46b5a repro-c 💥 possible deadlock in v2_write_dquot 2026/10/21 05:39 2026/10/21 05:39 2026/10/21 11:44 61c200c7
a38a4f79 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in v2_write_dquot 2026/10/20 00:04 2026/10/20 00:04 2026/10/20 01:01 e931f328
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Title Replies (including bot) Last reply
[syzbot] [fs?] possible deadlock in v2_write_dquot 0 (1) 2026/10/22 22:33

Sample crash report:
EXT4-fs (loop5): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
ext4 filesystem being mounted at /1334/file0 supports timestamps until 2038-01-19 (0x7fffffff)
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.5.7752/28220 is trying to acquire lock:
ffff8880535c6248 (&s->s_dquot.dqio_sem){++++}-{4:4}, at: v2_write_dquot+0xab/0x260 fs/quota/quota_v2.c:367

but task is already holding lock:
ffff88805537bca0 (&dquot->dq_lock){+.+.}-{4:4}, at: dquot_acquire+0x67/0x620 fs/quota/dquot.c:486

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #9 (&dquot->dq_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       wait_on_dquot fs/quota/dquot.c:357 [inline]
       dqget+0x69d/0xbd0 fs/quota/dquot.c:997
       __dquot_initialize+0x3c8/0xd40 fs/quota/dquot.c:1462
       __ext4_new_inode+0x7ed/0x3ec0 fs/ext4/ialloc.c:1004
       ext4_xattr_inode_create fs/ext4/xattr.c:1494 [inline]
       ext4_xattr_inode_lookup_create+0xb1e/0x1d70 fs/ext4/xattr.c:1604
       ext4_xattr_block_set+0x223/0x29a0 fs/ext4/xattr.c:1924
       ext4_xattr_set_handle+0xed9/0x15f0 fs/ext4/xattr.c:2461
       ext4_xattr_set+0x257/0x340 fs/ext4/xattr.c:2563
       __vfs_setxattr+0x442/0x480 fs/xattr.c:223
       __vfs_setxattr_noperm+0x12a/0x660 fs/xattr.c:257
       vfs_setxattr+0x163/0x360 fs/xattr.c:344
       do_setxattr fs/xattr.c:662 [inline]
       filename_setxattr+0x296/0x630 fs/xattr.c:690
       path_setxattrat+0x408/0x450 fs/xattr.c:734
       __do_sys_setxattr fs/xattr.c:768 [inline]
       __se_sys_setxattr fs/xattr.c:764 [inline]
       __x64_sys_setxattr+0xbc/0xe0 fs/xattr.c:764
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #8 (&ei->xattr_sem){++++}-{4:4}:
       down_write+0x96/0x200 kernel/locking/rwsem.c:1631
       ext4_write_lock_xattr fs/ext4/xattr.h:152 [inline]
       ext4_inline_data_truncate+0x1cf/0xbd0 fs/ext4/inline.c:1882
       ext4_truncate+0x444/0x1110 fs/ext4/inode.c:4650
       ext4_setattr+0x1147/0x1df0 fs/ext4/inode.c:6220
       notify_change+0xbba/0xea0 fs/attr.c:556
       do_truncate+0x1c2/0x250 fs/open.c:68
       handle_truncate fs/namei.c:4300 [inline]
       do_open fs/namei.c:4840 [inline]
       path_openat+0x185e/0x2090 fs/namei.c:4999
       do_file_open+0x23e/0x4a0 fs/namei.c:5028
       do_sys_openat2+0x115/0x200 fs/open.c:1417
       do_sys_open fs/open.c:1423 [inline]
       __do_sys_creat fs/open.c:1501 [inline]
       __se_sys_creat fs/open.c:1495 [inline]
       __x64_sys_creat+0x8f/0xc0 fs/open.c:1495
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #7 (mapping.invalidate_lock#2){++++}-{4:4}:
       down_read+0x4a/0x330 kernel/locking/rwsem.c:1574
       filemap_invalidate_lock_shared include/linux/fs.h:1089 [inline]
       do_page_cache_ra mm/readahead.c:347 [inline]
       page_cache_ra_order+0xb37/0xee0 mm/readahead.c:558
       do_sync_mmap_readahead+0x75e/0x990 mm/filemap.c:3443
       filemap_fault+0x7d9/0x13b0 mm/filemap.c:3597
       __do_fault+0x138/0x2a0 mm/memory.c:5565
       do_read_fault mm/memory.c:6000 [inline]
       do_fault mm/memory.c:6134 [inline]
       do_pte_missing+0x2215/0x34b0 mm/memory.c:4700
       handle_pte_fault mm/memory.c:6558 [inline]
       __handle_mm_fault mm/memory.c:6707 [inline]
       handle_mm_fault+0x1a53/0x3750 mm/memory.c:6876
       do_user_addr_fault+0x746/0x1340 arch/x86/mm/fault.c:1394
       handle_page_fault arch/x86/mm/fault.c:1483 [inline]
       exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
       asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
       copy_user_generic arch/x86/include/asm/uaccess_64.h:126 [inline]
       raw_copy_from_user arch/x86/include/asm/uaccess_64.h:141 [inline]
       copy_from_user_iter lib/iov_iter.c:67 [inline]
       iterate_ubuf include/linux/iov_iter.h:30 [inline]
       iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
       iterate_and_advance include/linux/iov_iter.h:330 [inline]
       __copy_from_iter lib/iov_iter.c:261 [inline]
       _copy_from_iter+0x216/0x1660 lib/iov_iter.c:272
       copy_from_iter include/linux/uio.h:228 [inline]
       copy_from_iter_full include/linux/uio.h:245 [inline]
       skb_do_copy_data_nocache include/net/sock.h:2329 [inline]
       skb_copy_to_page_nocache include/net/sock.h:2355 [inline]
       tcp_sendmsg_locked+0x20cf/0x5400 net/ipv4/tcp.c:1310
       tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1451
       sock_sendmsg_nosec+0x10e/0x180 net/socket.c:801
       __sock_sendmsg net/socket.c:815 [inline]
       sock_write_iter+0x2de/0x3e0 net/socket.c:1266
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x612/0xba0 fs/read_write.c:687
       ksys_write+0x150/0x270 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_sock_nested+0x41/0x100 net/core/sock.c:3837
       lock_sock include/net/sock.h:1713 [inline]
       inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:913
       nbd_mark_nsock_dead+0x2cb/0x550 drivers/block/nbd.c:319
       recv_work+0x1cee/0x1e10 drivers/block/nbd.c:1030
       process_one_work kernel/workqueue.c:3396 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560
       kthread+0x38b/0x480 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       nbd_handle_cmd drivers/block/nbd.c:1143 [inline]
       nbd_queue_rq+0x373/0xff0 drivers/block/nbd.c:1207
       blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2130
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0x16c/0x300 block/blk-mq.c:2545
       process_one_work kernel/workqueue.c:3396 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560
       kthread+0x38b/0x480 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #4 (&cmd->lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       nbd_queue_rq+0xc1/0xff0 drivers/block/nbd.c:1199
       blk_mq_dispatch_rq_list+0x499/0x1990 block/blk-mq.c:2130
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xd36/0x1580 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
       blk_mq_run_work_fn+0x16c/0x300 block/blk-mq.c:2545
       process_one_work kernel/workqueue.c:3396 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560
       kthread+0x38b/0x480 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #3 (set->srcu){.+.+}-{0:0}:
       srcu_lock_sync include/linux/srcu.h:210 [inline]
       __synchronize_srcu+0xc9/0x2f0 kernel/rcu/srcutree.c:1462
       elevator_switch+0x1e8/0x7b0 block/elevator.c:576
       elevator_change+0x2fa/0x480 block/elevator.c:681
       elevator_set_default+0x375/0x440 block/elevator.c:754
       blk_register_queue+0x3f3/0x4e0 block/blk-sysfs.c:992
       __add_disk+0x6b8/0xdb0 block/genhd.c:531
       add_disk_fwnode+0x100/0x3a0 block/genhd.c:600
       add_disk include/linux/blkdev.h:798 [inline]
       nbd_dev_add+0x733/0xb60 drivers/block/nbd.c:2026
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2743
       do_one_initcall+0x250/0x870 init/main.c:1362
       do_initcall_level+0x10a/0x1a0 init/main.c:1424
       do_initcalls+0x59/0xa0 init/main.c:1440
       kernel_init_freeable+0x29d/0x3e0 init/main.c:1675
       kernel_init+0x22/0x1d0 init/main.c:1565
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (&q->elevator_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821
       elevator_change+0x1af/0x480 block/elevator.c:679
       elv_iosched_store+0x504/0x630 block/elevator.c:826
       queue_attr_store+0x207/0x2b0 block/blk-sysfs.c:906
       kernfs_fop_write_iter+0x3a4/0x540 fs/kernfs/file.c:345
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x612/0xba0 fs/read_write.c:687
       ksys_write+0x150/0x270 fs/read_write.c:739
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#17){++++}-{0:0}:
       bio_queue_enter block/blk.h:95 [inline]
       blk_mq_submit_bio+0x7a7/0x2bb0 block/blk-mq.c:3138
       __submit_bio_noacct_mq block/blk-core.c:756 [inline]
       submit_bio_noacct_nocheck+0x2f4/0xa40 block/blk-core.c:790
       __ext4_read_bh fs/ext4/super.c:181 [inline]
       ext4_read_bh+0x182/0x230 fs/ext4/super.c:206
       ext4_bread+0x12d/0x180 fs/ext4/inode.c:1060
       ext4_quota_read+0x189/0x390 fs/ext4/super.c:7397
       read_blk fs/quota/quota_tree.c:61 [inline]
       find_tree_dqentry+0x1fc/0x1090 fs/quota/quota_tree.c:671
       find_tree_dqentry+0x6c0/0x1090 fs/quota/quota_tree.c:698
       find_tree_dqentry+0x6c0/0x1090 fs/quota/quota_tree.c:698
       find_tree_dqentry+0x6c0/0x1090 fs/quota/quota_tree.c:698
       find_dqentry fs/quota/quota_tree.c:716 [inline]
       qtree_read_dquot+0x5ac/0x8a0 fs/quota/quota_tree.c:736
       v2_read_dquot+0x117/0x1d0 fs/quota/quota_v2.c:344
       dquot_acquire+0x183/0x620 fs/quota/dquot.c:489
       ext4_acquire_dquot+0x2f0/0x4e0 fs/ext4/super.c:7075
       dqget+0x725/0xbd0 fs/quota/dquot.c:1002
       __dquot_initialize+0x33a/0xd40 fs/quota/dquot.c:1462
       ext4_rename fs/ext4/namei.c:3831 [inline]
       ext4_rename2+0x758/0x3270 fs/ext4/namei.c:4218
       vfs_rename+0xbd9/0xef0 fs/namei.c:6207
       filename_renameat2+0x533/0x9a0 fs/namei.c:6325
       __do_sys_renameat2 fs/namei.c:6354 [inline]
       __se_sys_renameat2+0x5a/0x2c0 fs/namei.c:6349
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&s->s_dquot.dqio_sem){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       down_write+0x96/0x200 kernel/locking/rwsem.c:1631
       v2_write_dquot+0xab/0x260 fs/quota/quota_v2.c:367
       dquot_acquire+0x328/0x620 fs/quota/dquot.c:498
       ext4_acquire_dquot+0x2f0/0x4e0 fs/ext4/super.c:7075
       dqget+0x725/0xbd0 fs/quota/dquot.c:1002
       dquot_set_dqblk+0x2b/0xfd0 fs/quota/dquot.c:2777
       quota_setquota+0x4e0/0x590 fs/quota/quota.c:310
       __do_sys_quotactl fs/quota/quota.c:961 [inline]
       __se_sys_quotactl+0x2cc/0x9f0 fs/quota/quota.c:917
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &s->s_dquot.dqio_sem --> &ei->xattr_sem --> &dquot->dq_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&dquot->dq_lock);
                               lock(&ei->xattr_sem);
                               lock(&dquot->dq_lock);
  lock(&s->s_dquot.dqio_sem);

 *** DEADLOCK ***

locks held by syz.5.7752/28220: 2, last CPU#0:
 #0: ffff8880535c60e8 (&type->s_umount_key#33){++++}-{4:4}, at: __super_lock fs/super.c:62 [inline]
 #0: ffff8880535c60e8 (&type->s_umount_key#33){++++}-{4:4}, at: super_lock+0x2d6/0x3d0 fs/super.c:124
 #1: ffff88805537bca0 (&dquot->dq_lock){+.+.}-{4:4}, at: dquot_acquire+0x67/0x620 fs/quota/dquot.c:486

stack backtrace:
CPU: 0 UID: 0 PID: 28220 Comm: syz.5.7752 Tainted: G             L      syzkaller #0 PREEMPT(lazy) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/05/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 down_write+0x96/0x200 kernel/locking/rwsem.c:1631
 v2_write_dquot+0xab/0x260 fs/quota/quota_v2.c:367
 dquot_acquire+0x328/0x620 fs/quota/dquot.c:498
 ext4_acquire_dquot+0x2f0/0x4e0 fs/ext4/super.c:7075
 dqget+0x725/0xbd0 fs/quota/dquot.c:1002
 dquot_set_dqblk+0x2b/0xfd0 fs/quota/dquot.c:2777
 quota_setquota+0x4e0/0x590 fs/quota/quota.c:310
 __do_sys_quotactl fs/quota/quota.c:961 [inline]
 __se_sys_quotactl+0x2cc/0x9f0 fs/quota/quota.c:917
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ffb1039e559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffb11205028 EFLAGS: 00000246 ORIG_RAX: 00000000000000b3
RAX: ffffffffffffffda RBX: 00007ffb10625fa0 RCX: 00007ffb1039e559
RDX: 0000000000000000 RSI: 0000200000000000 RDI: ffffffff80000801
RBP: 00007ffb10435ab8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000200000000100 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffb10626038 R14: 00007ffb10625fa0 R15: 00007fff0c429e18
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/18 22:27 upstream a0ff06b3a7bd 432c0077 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root possible deadlock in v2_write_dquot
* Struck through repros no longer work on HEAD.