[syzbot ci] Re: Create and use APIs to centralise locking for directory ops.

syzbot ci
2025-11-06T09:02:48Z

syzbot ci has tested the following series

[v5] Create and use APIs to centralise locking for directory ops.
https://lore.kernel.org/all/20251106005333.956321-1-neilb@ownmail.net
* [PATCH v5 01/14] debugfs: rename end_creating() to debugfs_end_creating()
* [PATCH v5 02/14] VFS: introduce start_dirop() and end_dirop()
* [PATCH v5 03/14] VFS: tidy up do_unlinkat()
* [PATCH v5 04/14] VFS/nfsd/cachefiles/ovl: add start_creating() and end_creating()
* [PATCH v5 05/14] VFS/nfsd/cachefiles/ovl: introduce start_removing() and end_removing()
* [PATCH v5 06/14] VFS: introduce start_creating_noperm() and start_removing_noperm()
* [PATCH v5 07/14] VFS: introduce start_removing_dentry()
* [PATCH v5 08/14] VFS: add start_creating_killable() and start_removing_killable()
* [PATCH v5 09/14] VFS/nfsd/ovl: introduce start_renaming() and end_renaming()
* [PATCH v5 10/14] VFS/ovl/smb: introduce start_renaming_dentry()
* [PATCH v5 11/14] Add start_renaming_two_dentries()
* [PATCH v5 12/14] ecryptfs: use new start_creating/start_removing APIs
* [PATCH v5 13/14] VFS: change vfs_mkdir() to unlock on failure.
* [PATCH v5 14/14] VFS: introduce end_creating_keep()

and found the following issues:
* WARNING: lock held when returning to user space in start_creating
* possible deadlock in mnt_want_write

Full report is available here:
https://ci.syzbot.org/series/4f406e4d-6aba-457a-b9c1-21f4407176a0

***

WARNING: lock held when returning to user space in start_creating

tree: torvalds
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base: 6146a0f1dfae5d37442a9ddcba012add260bceb0
arch: amd64
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config: https://ci.syzbot.org/builds/49013fb4-56ed-423c-8e15-252d65d5c1b4/config
C repro: https://ci.syzbot.org/findings/403597e5-81d3-4a9e-8d43-cf15c00b3265/c_repro
syz repro: https://ci.syzbot.org/findings/403597e5-81d3-4a9e-8d43-cf15c00b3265/syz_repro

UDF-fs: INFO Mounting volume 'LinuxUDF', timestamp 2022/11/22 14:59 (1000)
overlayfs: upper fs needs to support d_type.
overlayfs: upper fs does not support tmpfile.
================================================
WARNING: lock held when returning to user space!
syzkaller #0 Not tainted
------------------------------------------------
syz.0.17/5964 is leaving the kernel with locks still held!
1 lock held by syz.0.17/5964:
#0: ffff888119a282a0 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1025 [inline]
#0: ffff888119a282a0 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2794 [inline]
#0: ffff888119a282a0 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: start_dirop fs/namei.c:2805 [inline]
#0: ffff888119a282a0 (&type->i_mutex_dir_key#8/1){+.+.}-{4:4}, at: start_creating+0xbe/0x100 fs/namei.c:3261

***

possible deadlock in mnt_want_write

tree: torvalds
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base: 6146a0f1dfae5d37442a9ddcba012add260bceb0
arch: amd64
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config: https://ci.syzbot.org/builds/49013fb4-56ed-423c-8e15-252d65d5c1b4/config
syz repro: https://ci.syzbot.org/findings/7d1f626d-9979-4c5b-b36b-5616a983b0ac/syz_repro

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6011 is trying to acquire lock:
ffff88810943c420
(sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:508

but task is already holding lock:
ffff888169f40940 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1025 [inline]
ffff888169f40940 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2794 [inline]
ffff888169f40940 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}, at: start_dirop fs/namei.c:2805 [inline]
ffff888169f40940 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}, at: start_creating+0xbe/0x100 fs/namei.c:3261

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}:
reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
__lock_release kernel/locking/lockdep.c:5574 [inline]
lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
up_write+0x2d/0x420 kernel/locking/rwsem.c:1642
inode_unlock include/linux/fs.h:990 [inline]
end_dirop fs/namei.c:2818 [inline]
end_creating include/linux/namei.h:125 [inline]
vfs_mkdir+0x111/0x570 fs/namei.c:5037
do_mkdirat+0x247/0x5e0 fs/namei.c:5058
__do_sys_mkdir fs/namei.c:5080 [inline]
__se_sys_mkdir fs/namei.c:5078 [inline]
__x64_sys_mkdir+0x6c/0x80 fs/namei.c:5078
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (sb_writers#12){.+.+}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
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.h:1916 [inline]
sb_start_write+0x4d/0x1c0 include/linux/fs.h:2052
mnt_want_write+0x41/0x90 fs/namespace.c:508
filename_create+0x14f/0x360 fs/namei.c:4785
do_mkdirat+0x32c/0x5e0 fs/namei.c:5050
__do_sys_mkdir fs/namei.c:5080 [inline]
__se_sys_mkdir fs/namei.c:5078 [inline]
__x64_sys_mkdir+0x6c/0x80 fs/namei.c:5078
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&type->i_mutex_dir_key#5/1);
lock(sb_writers#12);
lock(&type->i_mutex_dir_key#5/1);
rlock(sb_writers#12);

*** DEADLOCK ***

1 lock held by syz.0.17/6011:
#0: ffff888169f40940 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:1025 [inline]
#0: ffff888169f40940 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}, at: __start_dirop fs/namei.c:2794 [inline]
#0: ffff888169f40940 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}, at: start_dirop fs/namei.c:2805 [inline]
#0: ffff888169f40940 (&type->i_mutex_dir_key#5/1){+.+.}-{4:4}, at: start_creating+0xbe/0x100 fs/namei.c:3261

stack backtrace:
CPU: 1 UID: 0 PID: 6011 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
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.h:1916 [inline]
sb_start_write+0x4d/0x1c0 include/linux/fs.h:2052
mnt_want_write+0x41/0x90 fs/namespace.c:508
filename_create+0x14f/0x360 fs/namei.c:4785
do_mkdirat+0x32c/0x5e0 fs/namei.c:5050
__do_sys_mkdir fs/namei.c:5080 [inline]
__se_sys_mkdir fs/namei.c:5078 [inline]
__x64_sys_mkdir+0x6c/0x80 fs/namei.c:5078
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdc9a98efc9
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:00007fdc9b79b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 00007fdc9abe5fa0 RCX: 00007fdc9a98efc9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00002000000008c0
RBP: 00007fdc9aa11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdc9abe6038 R14: 00007fdc9abe5fa0 R15: 00007ffe4d481c38
</TASK>

***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syzbot@syzkaller.appspotmail.com

---
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