Message-ID: <6824f447.a70a0220.3e9d8.001d.GAE@google.com>
Date: Wed, 14 May 2025 12:51:35 -0700
From: syzbot <syzbot+eb6f218811a9d721fd53@...kaller.appspotmail.com>
To: andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	pabeni@...hat.com, richardcochran@...il.com, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [net?] possible deadlock in ptp_clock_unregister

Hello,

syzbot found the following issue on:

HEAD commit:    405e6c37c89e Merge tag 'probes-fixes-v6.15-rc6' of git://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=132f4af4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7819b10245b63b3d
dashboard link: https://syzkaller.appspot.com/bug?extid=eb6f218811a9d721fd53
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/62d60a45311f/disk-405e6c37.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/63f63df5f19f/vmlinux-405e6c37.xz
kernel image: https://storage.googleapis.com/syzbot-assets/89438849afbb/bzImage-405e6c37.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+eb6f218811a9d721fd53@...kaller.appspotmail.com

ptp ptp0: delete virtual clock ptp1
============================================
WARNING: possible recursive locking detected
6.15.0-rc6-syzkaller-00051-g405e6c37c89e #0 Not tainted
--------------------------------------------
syz.0.550/8873 is trying to acquire lock:
ffff88802a6c4868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_vclock_in_use drivers/ptp/ptp_private.h:103 [inline]
ffff88802a6c4868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_clock_unregister+0x21/0x250 drivers/ptp/ptp_clock.c:415

but task is already holding lock:
ffff88814c752868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: n_vclocks_store+0xf1/0x6d0 drivers/ptp/ptp_sysfs.c:215

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&ptp->n_vclocks_mux);
  lock(&ptp->n_vclocks_mux);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

5 locks held by syz.0.550/8873:
 #0: ffff8880290f0b78 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2a2/0x370 fs/file.c:1213
 #1: ffff888035f5e420 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x12a/0x240 fs/read_write.c:736
 #2: ffff888059fa1488 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x510 fs/kernfs/file.c:325
 #3: ffff88814c93c878 (kn->active#100){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2b2/0x510 fs/kernfs/file.c:326
 #4: ffff88814c752868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: n_vclocks_store+0xf1/0x6d0 drivers/ptp/ptp_sysfs.c:215

stack backtrace:
CPU: 1 UID: 0 PID: 8873 Comm: syz.0.550 Not tainted 6.15.0-rc6-syzkaller-00051-g405e6c37c89e #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_deadlock_bug+0x1e9/0x240 kernel/locking/lockdep.c:3042
 check_deadlock kernel/locking/lockdep.c:3094 [inline]
 validate_chain kernel/locking/lockdep.c:3896 [inline]
 __lock_acquire+0xff7/0x1ba0 kernel/locking/lockdep.c:5235
 lock_acquire kernel/locking/lockdep.c:5866 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5823
 __mutex_lock_common kernel/locking/mutex.c:601 [inline]
 __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:746
 ptp_vclock_in_use drivers/ptp/ptp_private.h:103 [inline]
 ptp_clock_unregister+0x21/0x250 drivers/ptp/ptp_clock.c:415
 ptp_vclock_unregister+0x11a/0x160 drivers/ptp/ptp_vclock.c:228
 unregister_vclock+0x108/0x1a0 drivers/ptp/ptp_sysfs.c:177
 device_for_each_child_reverse+0x136/0x1a0 drivers/base/core.c:4051
 n_vclocks_store+0x4b6/0x6d0 drivers/ptp/ptp_sysfs.c:241
 dev_attr_store+0x58/0x80 drivers/base/core.c:2440
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
 kernfs_fop_write_iter+0x351/0x510 fs/kernfs/file.c:334
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0x5bd/0x1180 fs/read_write.c:684
 ksys_write+0x12a/0x240 fs/read_write.c:736
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f234fb8e969
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:00007f2350ade038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f234fdb5fa0 RCX: 00007f234fb8e969
RDX: 0000000000000004 RSI: 0000200000000100 RDI: 0000000000000005
RBP: 00007f234fc10ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f234fdb5fa0 R15: 00007ffea4834d58
 </TASK>
ptp ptp0: only physical clock in use now


---
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