Re: [syzbot] [ext4?] possible deadlock in wait_transaction_locked (3)

[Hillf Danton]

> On Sun, 22 Feb 2026 12:59:33 -0800
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    32a92f8c8932 Convert more 'alloc_obj' cases to default GFP..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16a7d95a580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=35a2f9886a9bccfa
> dashboard link: https://syzkaller.appspot.com/bug?extid=5d19358d7eb30ffb0cc5
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1543055a580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=104f8006580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/1c446301a138/disk-32a92f8c.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/245be1b900af/vmlinux-32a92f8c.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/16e0d6bc53db/bzImage-32a92f8c.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/1c55fb38005a/mount_0.gz
>   fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=14a3a55a580000)
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+5d19358d7eb30ffb0cc5@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> syzkaller #0 Not tainted
> ------------------------------------------------------
> kworker/u8:11/1186 is trying to acquire lock:
> ffff888036d5ebb0 (jbd2_handle){++++}-{0:0}, at: wait_transaction_locked+0x1a9/0x280 fs/jbd2/transaction.c:151
> 
> but task is already holding lock:
> ffff888036d52c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
> ffff888036d52c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_read fs/ext4/ext4.h:1813 [inline]
> ffff888036d52c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages+0x205/0x3b0 fs/ext4/inode.c:3018
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #2 (&sbi->s_writepages_rwsem){++++}-{0:0}:
>        percpu_down_read_internal+0x48/0x1d0 include/linux/percpu-rwsem.h:53
>        percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
>        ext4_writepages_down_read fs/ext4/ext4.h:1813 [inline]
>        ext4_writepages+0x205/0x3b0 fs/ext4/inode.c:3018
>        do_writepages+0x32e/0x550 mm/page-writeback.c:2554
>        __writeback_single_inode+0x133/0x11a0 fs/fs-writeback.c:1749
>        writeback_single_inode+0x488/0xd60 fs/fs-writeback.c:1868
>        write_inode_now+0x1c2/0x290 fs/fs-writeback.c:2953
>        iput_final fs/inode.c:1956 [inline]
>        iput+0x8c1/0xe80 fs/inode.c:2015
>        ext4_xattr_block_set+0x1fd4/0x2ad0 fs/ext4/xattr.c:2204
>        ext4_xattr_move_to_block fs/ext4/xattr.c:2669 [inline]
>        ext4_xattr_make_inode_space fs/ext4/xattr.c:2744 [inline]
>        ext4_expand_extra_isize_ea+0x12cf/0x1ea0 fs/ext4/xattr.c:2832
>        __ext4_expand_extra_isize+0x30d/0x400 fs/ext4/inode.c:6297
>        ext4_try_to_expand_extra_isize fs/ext4/inode.c:6340 [inline]
>        __ext4_mark_inode_dirty+0x45c/0x730 fs/ext4/inode.c:6418
>        ext4_evict_inode+0x7a1/0xeb0 fs/ext4/inode.c:255
>        evict+0x61e/0xb10 fs/inode.c:846
>        ext4_orphan_cleanup+0xc38/0x1470 fs/ext4/orphan.c:472
>        __ext4_fill_super fs/ext4/super.c:5668 [inline]
>        ext4_fill_super+0x5a0b/0x6320 fs/ext4/super.c:5791
>        get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
>        vfs_get_tree+0x92/0x2a0 fs/super.c:1754
>        fc_mount fs/namespace.c:1193 [inline]
>        do_new_mount_fc fs/namespace.c:3760 [inline]
>        do_new_mount+0x341/0xd30 fs/namespace.c:3836
>        do_mount fs/namespace.c:4159 [inline]
>        __do_sys_mount fs/namespace.c:4348 [inline]
>        __se_sys_mount+0x31d/0x420 fs/namespace.c:4325
>        do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>        do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> -> #1 (&ei->xattr_sem){++++}-{4:4}:
>        down_write+0x3a/0x50 kernel/locking/rwsem.c:1590
>        ext4_write_lock_xattr fs/ext4/xattr.h:157 [inline]
>        ext4_xattr_set_handle+0x19c/0x14c0 fs/ext4/xattr.c:2372
>        ext4_initxattrs+0x9f/0x110 fs/ext4/xattr_security.c:44
>        security_inode_init_security+0x296/0x3d0 security/security.c:1344
>        __ext4_new_inode+0x332f/0x3d20 fs/ext4/ialloc.c:1324
>        ext4_create+0x233/0x470 fs/ext4/namei.c:2820
>        lookup_open fs/namei.c:4483 [inline]
>        open_last_lookups fs/namei.c:4583 [inline]
>        path_openat+0x13b4/0x38a0 fs/namei.c:4827
>        do_file_open+0x23e/0x4a0 fs/namei.c:4859
>        do_sys_openat2+0x113/0x200 fs/open.c:1366
>        do_sys_open fs/open.c:1372 [inline]
>        __do_sys_openat fs/open.c:1388 [inline]
>        __se_sys_openat fs/open.c:1383 [inline]
>        __x64_sys_openat+0x138/0x170 fs/open.c:1383
>        do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>        do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> -> #0 (jbd2_handle){++++}-{0:0}:
>        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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
>        lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
>        wait_transaction_locked+0x1c2/0x280 fs/jbd2/transaction.c:151
>        add_transaction_credits fs/jbd2/transaction.c:222 [inline]
>        start_this_handle+0x7dc/0x2290 fs/jbd2/transaction.c:403
>        jbd2__journal_start+0x2c0/0x5b0 fs/jbd2/transaction.c:501
>        __ext4_journal_start_sb+0x203/0x620 fs/ext4/ext4_jbd2.c:114
>        __ext4_journal_start fs/ext4/ext4_jbd2.h:242 [inline]
>        ext4_do_writepages+0xf97/0x46e0 fs/ext4/inode.c:2907
>        ext4_writepages+0x241/0x3b0 fs/ext4/inode.c:3019
>        do_writepages+0x32e/0x550 mm/page-writeback.c:2554
>        __writeback_single_inode+0x133/0x11a0 fs/fs-writeback.c:1749
>        writeback_sb_inodes+0x944/0x1970 fs/fs-writeback.c:2040
>        __writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:2117
>        wb_writeback+0x46a/0xb70 fs/fs-writeback.c:2228
>        wb_check_old_data_flush fs/fs-writeback.c:2332 [inline]
>        wb_do_writeback fs/fs-writeback.c:2385 [inline]
>        wb_workfn+0xb52/0xf60 fs/fs-writeback.c:2413

Given mount reported still in progress, flusher has no chance to kick off, thus
this report sounds false positive.

>        process_one_work kernel/workqueue.c:3275 [inline]
>        process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
>        worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
>        kthread+0x388/0x470 kernel/kthread.c:467
>        ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> 
> other info that might help us debug this:
> 
> Chain exists of:
>   jbd2_handle --> &ei->xattr_sem --> &sbi->s_writepages_rwsem
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   rlock(&sbi->s_writepages_rwsem);
>                                lock(&ei->xattr_sem);
>                                lock(&sbi->s_writepages_rwsem);
>   lock(jbd2_handle);
> 
>  *** DEADLOCK ***
> 
> 4 locks held by kworker/u8:11/1186:
>  #0: ffff88801f6af138 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3250 [inline]
>  #0: ffff88801f6af138 ((wq_completion)writeback){+.+.}-{0:0}, at: process_scheduled_works+0x9ea/0x1830 kernel/workqueue.c:3358
>  #1: ffffc90006487c40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
>  #1: ffffc90006487c40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_scheduled_works+0xa25/0x1830 kernel/workqueue.c:3358
>  #2: ffff888036d540d0 (&type->s_umount_key#32){++++}-{4:4}, at: super_trylock_shared+0x20/0xf0 fs/super.c:565
>  #3: ffff888036d52c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: percpu_down_read include/linux/percpu-rwsem.h:77 [inline]
>  #3: ffff888036d52c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages_down_read fs/ext4/ext4.h:1813 [inline]
>  #3: ffff888036d52c58 (&sbi->s_writepages_rwsem){++++}-{0:0}, at: ext4_writepages+0x205/0x3b0 fs/ext4/inode.c:3018
> 
> stack backtrace:
> CPU: 1 UID: 0 PID: 1186 Comm: kworker/u8:11 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
> Workqueue: writeback wb_workfn (flush-8:0)
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
>  print_circular_bug+0x2e1/0x300 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
>  lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868
>  wait_transaction_locked+0x1c2/0x280 fs/jbd2/transaction.c:151
>  add_transaction_credits fs/jbd2/transaction.c:222 [inline]
>  start_this_handle+0x7dc/0x2290 fs/jbd2/transaction.c:403
>  jbd2__journal_start+0x2c0/0x5b0 fs/jbd2/transaction.c:501
>  __ext4_journal_start_sb+0x203/0x620 fs/ext4/ext4_jbd2.c:114
>  __ext4_journal_start fs/ext4/ext4_jbd2.h:242 [inline]
>  ext4_do_writepages+0xf97/0x46e0 fs/ext4/inode.c:2907
>  ext4_writepages+0x241/0x3b0 fs/ext4/inode.c:3019
>  do_writepages+0x32e/0x550 mm/page-writeback.c:2554
>  __writeback_single_inode+0x133/0x11a0 fs/fs-writeback.c:1749
>  writeback_sb_inodes+0x944/0x1970 fs/fs-writeback.c:2040
>  __writeback_inodes_wb+0x111/0x240 fs/fs-writeback.c:2117
>  wb_writeback+0x46a/0xb70 fs/fs-writeback.c:2228
>  wb_check_old_data_flush fs/fs-writeback.c:2332 [inline]
>  wb_do_writeback fs/fs-writeback.c:2385 [inline]
>  wb_workfn+0xb52/0xf60 fs/fs-writeback.c:2413
>  process_one_work kernel/workqueue.c:3275 [inline]
>  process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
>  worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
>  kthread+0x388/0x470 kernel/kthread.c:467
>  ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>