syzbot


possible deadlock in dqget (2)

Status: upstream: reported on 2025/06/30 17:34
Reported-by: syzbot+48f6149796b9cd8dc4e4@syzkaller.appspotmail.com
First crash: 21d, last: 21d
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 possible deadlock in dqget 4 11 3d21h 32d 0/2 upstream: reported on 2025/06/20 12:37
linux-6.1 possible deadlock in dqget 4 1 175d 175d 0/3 auto-obsoleted due to no activity on 2025/05/07 22:20
upstream possible deadlock in dqget ocfs2 ext4 4 C error 71814 18m 294d 0/29 upstream: reported C repro on 2024/10/01 08:09

Sample crash report:
EXT4-fs: Journaled quota options ignored when QUOTA feature is enabled
EXT4-fs (loop2): mounted filesystem without journal. Quota mode: writeback.
======================================================
WARNING: possible circular locking dependency detected
6.1.142-syzkaller #0 Not tainted
------------------------------------------------------
syz.2.11138/30581 is trying to acquire lock:
ffff888072421228 (&dquot->dq_lock){+.+.}-{3:3}, at: wait_on_dquot fs/quota/dquot.c:356 [inline]
ffff888072421228 (&dquot->dq_lock){+.+.}-{3:3}, at: dqget+0x6f8/0xeb0 fs/quota/dquot.c:983

but task is already holding lock:
ffff888059085b10 (&ei->xattr_sem){++++}-{3:3}, at: ext4_setattr+0x92a/0x19f0 fs/ext4/inode.c:5501

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (&ei->xattr_sem){++++}-{3:3}:
       down_read+0x42/0x2d0 kernel/locking/rwsem.c:1520
       ext4_setattr+0x92a/0x19f0 fs/ext4/inode.c:5501
       notify_change+0xc74/0xf40 fs/attr.c:499
       chown_common+0x486/0x620 fs/open.c:736
       do_fchownat+0x164/0x270 fs/open.c:767
       __do_sys_chown fs/open.c:787 [inline]
       __se_sys_chown fs/open.c:785 [inline]
       __x64_sys_chown+0x7e/0x90 fs/open.c:785
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #4 (jbd2_handle){++++}-{0:0}:
       start_this_handle+0x1f49/0x2150 fs/jbd2/transaction.c:463
       jbd2__journal_start+0x2b7/0x5a0 fs/jbd2/transaction.c:520
       jbd2_journal_start+0x26/0x30 fs/jbd2/transaction.c:559
       ocfs2_start_trans+0x372/0x6c0 fs/ocfs2/journal.c:376
       ocfs2_shutdown_local_alloc+0x1fd/0xa10 fs/ocfs2/localalloc.c:416
       ocfs2_dismount_volume+0x1fc/0x930 fs/ocfs2/super.c:1882
       generic_shutdown_super+0x130/0x340 fs/super.c:501
       kill_block_super+0x7c/0xe0 fs/super.c:1470
       deactivate_locked_super+0x93/0xf0 fs/super.c:332
       cleanup_mnt+0x463/0x4f0 fs/namespace.c:1182
       task_work_run+0x1ca/0x250 kernel/task_work.c:203
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
       exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:210
       __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
       syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
       do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #3 (&journal->j_trans_barrier){.+.+}-{3:3}:
       down_read+0x42/0x2d0 kernel/locking/rwsem.c:1520
       ocfs2_start_trans+0x366/0x6c0 fs/ocfs2/journal.c:374
       ocfs2_shutdown_local_alloc+0x1fd/0xa10 fs/ocfs2/localalloc.c:416
       ocfs2_dismount_volume+0x1fc/0x930 fs/ocfs2/super.c:1882
       generic_shutdown_super+0x130/0x340 fs/super.c:501
       kill_block_super+0x7c/0xe0 fs/super.c:1470
       deactivate_locked_super+0x93/0xf0 fs/super.c:332
       cleanup_mnt+0x463/0x4f0 fs/namespace.c:1182
       task_work_run+0x1ca/0x250 kernel/task_work.c:203
       resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
       exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
       exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:210
       __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
       syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
       do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #2 (sb_internal#2){.+.+}-{0:0}:
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write include/linux/fs.h:1891 [inline]
       sb_start_intwrite include/linux/fs.h:2013 [inline]
       ocfs2_start_trans+0x267/0x6c0 fs/ocfs2/journal.c:372
       ocfs2_acquire_dquot+0x66e/0xb10 fs/ocfs2/quota_global.c:848
       dqget+0x778/0xeb0 fs/quota/dquot.c:988
       dquot_set_dqblk+0x27/0xf90 fs/quota/dquot.c:2833
       quota_setquota+0x4ac/0x530 fs/quota/quota.c:310
       __do_sys_quotactl fs/quota/quota.c:960 [inline]
       __se_sys_quotactl+0x295/0x6b0 fs/quota/quota.c:916
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&ocfs2_quota_ip_alloc_sem_key){++++}-{3:3}:
       down_write+0x36/0x60 kernel/locking/rwsem.c:1573
       ocfs2_create_local_dquot+0x1a0/0x1790 fs/ocfs2/quota_local.c:1224
       ocfs2_acquire_dquot+0x7ae/0xb10 fs/ocfs2/quota_global.c:871
       dqget+0x778/0xeb0 fs/quota/dquot.c:988
       dquot_set_dqblk+0x27/0xf90 fs/quota/dquot.c:2833
       quota_setquota+0x4ac/0x530 fs/quota/quota.c:310
       __do_sys_quotactl fs/quota/quota.c:960 [inline]
       __se_sys_quotactl+0x295/0x6b0 fs/quota/quota.c:916
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (&dquot->dq_lock){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain kernel/locking/lockdep.c:3825 [inline]
       __lock_acquire+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
       lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x120/0xaf0 kernel/locking/mutex.c:747
       wait_on_dquot fs/quota/dquot.c:356 [inline]
       dqget+0x6f8/0xeb0 fs/quota/dquot.c:983
       dquot_transfer+0x63f/0x820 fs/quota/dquot.c:2164
       ext4_setattr+0x93d/0x19f0 fs/ext4/inode.c:5502
       notify_change+0xc74/0xf40 fs/attr.c:499
       chown_common+0x486/0x620 fs/open.c:736
       do_fchownat+0x164/0x270 fs/open.c:767
       __do_sys_chown fs/open.c:787 [inline]
       __se_sys_chown fs/open.c:785 [inline]
       __x64_sys_chown+0x7e/0x90 fs/open.c:785
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

Chain exists of:
  &dquot->dq_lock --> jbd2_handle --> &ei->xattr_sem

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&ei->xattr_sem);
                               lock(jbd2_handle);
                               lock(&ei->xattr_sem);
  lock(&dquot->dq_lock);

 *** DEADLOCK ***

3 locks held by syz.2.11138/30581:
 #0: ffff88801a6c2460 (sb_writers#4){.+.+}-{0:0}, at: mnt_want_write+0x3d/0x90 fs/namespace.c:393
 #1: ffff888059085e48 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: inode_lock include/linux/fs.h:758 [inline]
 #1: ffff888059085e48 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: chown_common+0x320/0x620 fs/open.c:726
 #2: ffff888059085b10 (&ei->xattr_sem){++++}-{3:3}, at: ext4_setattr+0x92a/0x19f0 fs/ext4/inode.c:5501

stack backtrace:
CPU: 1 PID: 30581 Comm: syz.2.11138 Not tainted 6.1.142-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
 check_noncircular+0x274/0x310 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3090 [inline]
 check_prevs_add kernel/locking/lockdep.c:3209 [inline]
 validate_chain kernel/locking/lockdep.c:3825 [inline]
 __lock_acquire+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
 lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
 __mutex_lock_common kernel/locking/mutex.c:603 [inline]
 __mutex_lock+0x120/0xaf0 kernel/locking/mutex.c:747
 wait_on_dquot fs/quota/dquot.c:356 [inline]
 dqget+0x6f8/0xeb0 fs/quota/dquot.c:983
 dquot_transfer+0x63f/0x820 fs/quota/dquot.c:2164
 ext4_setattr+0x93d/0x19f0 fs/ext4/inode.c:5502
 notify_change+0xc74/0xf40 fs/attr.c:499
 chown_common+0x486/0x620 fs/open.c:736
 do_fchownat+0x164/0x270 fs/open.c:767
 __do_sys_chown fs/open.c:787 [inline]
 __se_sys_chown fs/open.c:785 [inline]
 __x64_sys_chown+0x7e/0x90 fs/open.c:785
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f941618e929
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:00007f9416f88038 EFLAGS: 00000246 ORIG_RAX: 000000000000005c
RAX: ffffffffffffffda RBX: 00007f94163b5fa0 RCX: 00007f941618e929
RDX: 000000000000ee00 RSI: ffffffffffffffff RDI: 0000200000000040
RBP: 00007f9416210b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f94163b5fa0 R15: 00007ffd7573a0d8
 </TASK>
Quota error (device loop2): do_check_range: Getting dqdh_prev_free 1792 out of range 0-6
Quota error (device loop2): qtree_write_dquot: Error -117 occurred while creating quota
EXT4-fs error (device loop2): ext4_acquire_dquot:6814: comm syz.2.11138: Failed to acquire dquot type 1

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/30 17:33 linux-6.1.y 7e69c33e4858 6e83b42d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan possible deadlock in dqget
* Struck through repros no longer work on HEAD.