Re: [syzbot] [overlayfs?] possible deadlock in ovl_copy_up_start (5)

On Wed, Jun 17, 2026 at 11:09 PM syzbot
<[email protected]> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    596d152bc5e3 Merge branch 'for-next/core' into for-kernelci
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
> console output: https://syzkaller.appspot.com/x/log.txt?x=10aba8ae580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=eb40ba923a822433
> dashboard link: https://syzkaller.appspot.com/bug?extid=d4e3aadc5bd19f7e71ff
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> userspace arch: arm64
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/32d15acc8c01/disk-596d152b.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/83b3d8d84761/vmlinux-596d152b.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/8edfcc3bf911/Image-596d152b.gz.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email protected]
>
> ======================================================
> WARNING: possible circular locking dependency detected
> syzkaller #0 Tainted: G             L
> ------------------------------------------------------
> syz.3.611/8517 is trying to acquire lock:
> ffff0000eee140f8 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:705 [inline]
> ffff0000eee140f8 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_copy_up_start+0x58/0x264 fs/overlayfs/util.c:735
>
> but task is already holding lock:
> ffff0000eee13d88 (&ovl_i_mutex_key[depth]/4){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1074 [inline]
> ffff0000eee13d88 (&ovl_i_mutex_key[depth]/4){+.+.}-{4:4}, at: lock_two_nondirectories+0xe8/0x148 fs/inode.c:1256
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #2 (&ovl_i_mutex_key[depth]/4){+.+.}-{4:4}:
>        __lock_release kernel/locking/lockdep.c:5574 [inline]
>        lock_release+0x178/0x3b0 kernel/locking/lockdep.c:5889
>        up_write+0x3c/0x5d8 kernel/locking/rwsem.c:1681
>        inode_unlock include/linux/fs.h:1039 [inline]
>        unlock_two_nondirectories+0x60/0x118 fs/inode.c:1269
>        ext4_move_extents+0x468/0x3580 fs/ext4/move_extent.c:656
>        __ext4_ioctl fs/ext4/ioctl.c:1657 [inline]
>        ext4_ioctl+0x2a14/0x4234 fs/ext4/ioctl.c:1922
>        vfs_ioctl fs/ioctl.c:51 [inline]
>        __do_sys_ioctl fs/ioctl.c:597 [inline]
>        __se_sys_ioctl fs/ioctl.c:583 [inline]
>        __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
>        __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
>        invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
>        el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:121
>        do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:140
>        el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
>        el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
>        el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
>
> -> #1 (sb_writers#3){.+.+}-{0:0}:
>        percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
>        percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
>        __sb_start_write include/linux/fs/super.h:19 [inline]
>        sb_start_write include/linux/fs/super.h:125 [inline]
>        ovl_start_write+0xf0/0x324 fs/overlayfs/util.c:32
>        ovl_do_copy_up fs/overlayfs/copy_up.c:977 [inline]
>        ovl_copy_up_one fs/overlayfs/copy_up.c:1189 [inline]
>        ovl_copy_up_flags+0x980/0x28a4 fs/overlayfs/copy_up.c:1243
>        ovl_maybe_copy_up+0x108/0x148 fs/overlayfs/copy_up.c:1272
>        ovl_open+0x12c/0x2c0 fs/overlayfs/file.c:211
>        do_dentry_open+0x5c4/0xfc8 fs/open.c:947
>        vfs_open+0x44/0x2d4 fs/open.c:1079
>        do_open fs/namei.c:4699 [inline]
>        path_openat+0x2234/0x2a6c fs/namei.c:4858
>        do_file_open+0x1c4/0x2e4 fs/namei.c:4887
>        do_sys_openat2+0x114/0x1e8 fs/open.c:1364
>        do_sys_open+0xac/0xdc fs/open.c:1370
>        __do_sys_openat fs/open.c:1386 [inline]
>        __se_sys_openat fs/open.c:1381 [inline]
>        __arm64_sys_openat+0x9c/0xb8 fs/open.c:1381
>        __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
>        invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
>        el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:121
>        do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:140
>        el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
>        el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
>        el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
>
> -> #0 (&ovl_i_lock_key[depth]){+.+.}-{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+0x1780/0x2f44 kernel/locking/lockdep.c:5237
>        lock_acquire+0x140/0x368 kernel/locking/lockdep.c:5868
>        __mutex_lock_common kernel/locking/mutex.c:646 [inline]
>        __mutex_lock+0x160/0xef8 kernel/locking/mutex.c:820
>        mutex_lock_interruptible_nested+0x24/0x30 kernel/locking/mutex.c:898
>        ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:705 [inline]
>        ovl_copy_up_start+0x58/0x264 fs/overlayfs/util.c:735
>        ovl_copy_up_one fs/overlayfs/copy_up.c:1182 [inline]
>        ovl_copy_up_flags+0x768/0x28a4 fs/overlayfs/copy_up.c:1243
>        ovl_copy_up+0x24/0x34 fs/overlayfs/copy_up.c:1282
>        ovl_rename_start fs/overlayfs/dir.c:1176 [inline]
>        ovl_rename+0x2d8/0xfec fs/overlayfs/dir.c:1363
>        vfs_rename+0xa78/0xd48 fs/namei.c:6064
>        filename_renameat2+0x66c/0x730 fs/namei.c:6182
>        __do_sys_renameat2 fs/namei.c:6211 [inline]
>        __se_sys_renameat2 fs/namei.c:6206 [inline]
>        __arm64_sys_renameat2+0xe4/0x114 fs/namei.c:6206
>        __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
>        invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
>        el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:121
>        do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:140
>        el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
>        el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
>        el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
>
> other info that might help us debug this:
>
> Chain exists of:
>   &ovl_i_lock_key[depth] --> sb_writers#3 --> &ovl_i_mutex_key[depth]/4
>
>  Possible unsafe locking scenario:
>
>        CPU0                    CPU1
>        ----                    ----
>   lock(&ovl_i_mutex_key[depth]/4);
>                                lock(sb_writers#3);
>                                lock(&ovl_i_mutex_key[depth]/4);
>   lock(&ovl_i_lock_key[depth]);
>
>  *** DEADLOCK ***
>
> 5 locks held by syz.3.611/8517:
>  #0: ffff00010bddc410 (sb_writers#17){.+.+}-{0:0}, at: mnt_want_write+0x44/0x9c fs/namespace.c:493
>  #1: ffff00010bddc718 (&type->s_vfs_rename_key#3){+.+.}-{4:4}, at: lock_rename fs/namei.c:3791 [inline]
>  #1: ffff00010bddc718 (&type->s_vfs_rename_key#3){+.+.}-{4:4}, at: __start_renaming+0xec/0x33c fs/namei.c:3880
>  #2: ffff0000eee14300 (&ovl_i_mutex_dir_key[depth]/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1074 [inline]
>  #2: ffff0000eee14300 (&ovl_i_mutex_dir_key[depth]/1){+.+.}-{4:4}, at: lock_two_directories+0x19c/0x214 fs/namei.c:3767
>  #3: ffff0000eee13810 (&ovl_i_mutex_dir_key[depth]/5){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1074 [inline]
>  #3: ffff0000eee13810 (&ovl_i_mutex_dir_key[depth]/5){+.+.}-{4:4}, at: lock_two_directories+0x1c4/0x214 fs/namei.c:3768
>  #4: ffff0000eee13d88 (&ovl_i_mutex_key[depth]/4){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1074 [inline]
>  #4: ffff0000eee13d88 (&ovl_i_mutex_key[depth]/4){+.+.}-{4:4}, at: lock_two_nondirectories+0xe8/0x148 fs/inode.c:1256
>
> stack backtrace:
> CPU: 1 UID: 0 PID: 8517 Comm: syz.3.611 Tainted: G             L      syzkaller #0 PREEMPT
> Tainted: [L]=SOFTLOCKUP
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
> Call trace:
>  show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
>  __dump_stack+0x30/0x40 lib/dump_stack.c:94
>  dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
>  dump_stack+0x1c/0x28 lib/dump_stack.c:129
>  print_circular_bug+0x328/0x330 kernel/locking/lockdep.c:2043
>  check_noncircular+0x158/0x174 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+0x1780/0x2f44 kernel/locking/lockdep.c:5237
>  lock_acquire+0x140/0x368 kernel/locking/lockdep.c:5868
>  __mutex_lock_common kernel/locking/mutex.c:646 [inline]
>  __mutex_lock+0x160/0xef8 kernel/locking/mutex.c:820
>  mutex_lock_interruptible_nested+0x24/0x30 kernel/locking/mutex.c:898
>  ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:705 [inline]
>  ovl_copy_up_start+0x58/0x264 fs/overlayfs/util.c:735
>  ovl_copy_up_one fs/overlayfs/copy_up.c:1182 [inline]
>  ovl_copy_up_flags+0x768/0x28a4 fs/overlayfs/copy_up.c:1243
>  ovl_copy_up+0x24/0x34 fs/overlayfs/copy_up.c:1282
>  ovl_rename_start fs/overlayfs/dir.c:1176 [inline]
>  ovl_rename+0x2d8/0xfec fs/overlayfs/dir.c:1363
>  vfs_rename+0xa78/0xd48 fs/namei.c:6064
>  filename_renameat2+0x66c/0x730 fs/namei.c:6182
>  __do_sys_renameat2 fs/namei.c:6211 [inline]
>  __se_sys_renameat2 fs/namei.c:6206 [inline]
>  __arm64_sys_renameat2+0xe4/0x114 fs/namei.c:6206
>  __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
>  invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
>  el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:121
>  do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:140
>  el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
>  el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
>  el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
>
>
> ---
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#syz dup: possible deadlock in lock_two_nondirectories (2)

ext4 bug should be fixed in linux-next I think.

Thanks,
Amir.