ptp ptp0: new virtual clock ptp1
ptp ptp0: guarantee physical clock free running
ptp ptp0: delete virtual clock ptp1
ptp ptp0: only physical clock in use now
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/4426 is trying to acquire lock:
ffff88802964d8f0 (&ptp->n_vclocks_mux){+.+.}-{3:3}, at: ptp_vclock_in_use drivers/ptp/ptp_private.h:104 [inline]
ffff88802964d8f0 (&ptp->n_vclocks_mux){+.+.}-{3:3}, at: ptp_clock_freerun drivers/ptp/ptp_private.h:121 [inline]
ffff88802964d8f0 (&ptp->n_vclocks_mux){+.+.}-{3:3}, at: ptp_clock_settime+0x174/0x280 drivers/ptp/ptp_clock.c:81

but task is already holding lock:
ffff88802964c130 (&clk->rwsem){++++}-{3:3}, at: get_posix_clock kernel/time/posix-clock.c:25 [inline]
ffff88802964c130 (&clk->rwsem){++++}-{3:3}, at: get_clock_desc kernel/time/posix-clock.c:232 [inline]
ffff88802964c130 (&clk->rwsem){++++}-{3:3}, at: pc_clock_settime+0x17c/0x2a0 kernel/time/posix-clock.c:317

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&clk->rwsem){++++}-{3:3}:
       down_write+0x36/0x60 kernel/locking/rwsem.c:1573
       posix_clock_unregister+0x5b/0xc0 kernel/time/posix-clock.c:207
       ptp_clock_unregister+0x18a/0x200 drivers/ptp/ptp_clock.c:391
       ptp_vclock_unregister+0x110/0x140 drivers/ptp/ptp_vclock.c:230
       unregister_vclock+0xca/0x130 drivers/ptp/ptp_sysfs.c:164
       device_for_each_child_reverse+0x112/0x1b0 drivers/base/core.c:4073
       n_vclocks_store+0x226/0x750 drivers/ptp/ptp_sysfs.c:228
       kernfs_fop_write_iter+0x3a0/0x520 fs/kernfs/file.c:352
       call_write_iter include/linux/fs.h:2271 [inline]
       new_sync_write fs/read_write.c:491 [inline]
       vfs_write+0x482/0x9a0 fs/read_write.c:584
       ksys_write+0x14d/0x260 fs/read_write.c:637
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (&ptp->n_vclocks_mux){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3162 [inline]
       check_prevs_add kernel/locking/lockdep.c:3281 [inline]
       validate_chain kernel/locking/lockdep.c:3897 [inline]
       __lock_acquire+0x3a03/0x7ea0 kernel/locking/lockdep.c:5171
       lock_acquire+0x1bc/0x4a0 kernel/locking/lockdep.c:5790
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747
       ptp_vclock_in_use drivers/ptp/ptp_private.h:104 [inline]
       ptp_clock_freerun drivers/ptp/ptp_private.h:121 [inline]
       ptp_clock_settime+0x174/0x280 drivers/ptp/ptp_clock.c:81
       pc_clock_settime+0x23c/0x2a0 kernel/time/posix-clock.c:327
       __do_sys_clock_settime kernel/time/posix-timers.c:1125 [inline]
       __se_sys_clock_settime kernel/time/posix-timers.c:1113 [inline]
       __x64_sys_clock_settime+0x25a/0x2a0 kernel/time/posix-timers.c:1113
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&clk->rwsem);
                               lock(&ptp->n_vclocks_mux);
                               lock(&clk->rwsem);
  lock(&ptp->n_vclocks_mux);

 *** DEADLOCK ***

1 lock held by syz.0.17/4426:
 #0: ffff88802964c130 (&clk->rwsem){++++}-{3:3}, at: get_posix_clock kernel/time/posix-clock.c:25 [inline]
 #0: ffff88802964c130 (&clk->rwsem){++++}-{3:3}, at: get_clock_desc kernel/time/posix-clock.c:232 [inline]
 #0: ffff88802964c130 (&clk->rwsem){++++}-{3:3}, at: pc_clock_settime+0x17c/0x2a0 kernel/time/posix-clock.c:317

stack backtrace:
CPU: 0 PID: 4426 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 check_noncircular+0x2f8/0x400 kernel/locking/lockdep.c:2215
 check_prev_add kernel/locking/lockdep.c:3162 [inline]
 check_prevs_add kernel/locking/lockdep.c:3281 [inline]
 validate_chain kernel/locking/lockdep.c:3897 [inline]
 __lock_acquire+0x3a03/0x7ea0 kernel/locking/lockdep.c:5171
 lock_acquire+0x1bc/0x4a0 kernel/locking/lockdep.c:5790
 __mutex_lock_common kernel/locking/mutex.c:603 [inline]
 __mutex_lock+0x12d/0xae0 kernel/locking/mutex.c:747
 ptp_vclock_in_use drivers/ptp/ptp_private.h:104 [inline]
 ptp_clock_freerun drivers/ptp/ptp_private.h:121 [inline]
 ptp_clock_settime+0x174/0x280 drivers/ptp/ptp_clock.c:81
 pc_clock_settime+0x23c/0x2a0 kernel/time/posix-clock.c:327
 __do_sys_clock_settime kernel/time/posix-timers.c:1125 [inline]
 __se_sys_clock_settime kernel/time/posix-timers.c:1113 [inline]
 __x64_sys_clock_settime+0x25a/0x2a0 kernel/time/posix-timers.c:1113
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7ff47d79e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffda8a3c878 EFLAGS: 00000246 ORIG_RAX: 00000000000000e3
RAX: ffffffffffffffda RBX: 00007ff47da25fa0 RCX: 00007ff47d79e159
RDX: 0000000000000000 RSI: 0000200000000140 RDI: 00000000fffffffb
RBP: 00007ff47d83506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff47da25fac R14: 00007ff47da25fa0 R15: 00007ff47da25fa0
 </TASK>