syzbot

======================================================
WARNING: possible circular locking dependency detected
6.17.0-rc1-syzkaller-00038-g0cc53520e68b #0 Not tainted
------------------------------------------------------
syz.7.4518/28069 is trying to acquire lock:
ffff88802fdc2870 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_vclock_in_use drivers/ptp/ptp_private.h:113 [inline]
ffff88802fdc2870 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_vclock_in_use drivers/ptp/ptp_private.h:99 [inline]
ffff88802fdc2870 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_clock_freerun drivers/ptp/ptp_private.h:130 [inline]
ffff88802fdc2870 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_clock_freerun drivers/ptp/ptp_private.h:125 [inline]
ffff88802fdc2870 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: ptp_clock_adjtime+0x527/0x760 drivers/ptp/ptp_clock.c:125

but task is already holding lock:
ffff88802fdc2130 (&clk->rwsem){++++}-{4:4}, at: get_posix_clock kernel/time/posix-clock.c:25 [inline]
ffff88802fdc2130 (&clk->rwsem){++++}-{4:4}, at: get_clock_desc+0x125/0x240 kernel/time/posix-clock.c:209

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&clk->rwsem){++++}-{4:4}:
       down_write+0x92/0x200 kernel/locking/rwsem.c:1590
       posix_clock_unregister+0x4d/0xd0 kernel/time/posix-clock.c:184
       ptp_clock_unregister+0x14f/0x250 drivers/ptp/ptp_clock.c:432
       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+0x133/0x1a0 drivers/base/core.c:4048
       n_vclocks_store+0x4b6/0x6d0 drivers/ptp/ptp_sysfs.c:241
       dev_attr_store+0x58/0x80 drivers/base/core.c:2437
       sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:145
       kernfs_fop_write_iter+0x354/0x510 fs/kernfs/file.c:334
       new_sync_write fs/read_write.c:593 [inline]
       vfs_write+0x7d0/0x11d0 fs/read_write.c:686
       ksys_write+0x12a/0x250 fs/read_write.c:738
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&ptp->n_vclocks_mux){+.+.}-{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+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
       lock_acquire kernel/locking/lockdep.c:5868 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x193/0x10b0 kernel/locking/mutex.c:760
       ptp_vclock_in_use drivers/ptp/ptp_private.h:113 [inline]
       ptp_vclock_in_use drivers/ptp/ptp_private.h:99 [inline]
       ptp_clock_freerun drivers/ptp/ptp_private.h:130 [inline]
       ptp_clock_freerun drivers/ptp/ptp_private.h:125 [inline]
       ptp_clock_adjtime+0x527/0x760 drivers/ptp/ptp_clock.c:125
       pc_clock_adjtime+0x115/0x1e0 kernel/time/posix-clock.c:239
       do_clock_adjtime kernel/time/posix-timers.c:1162 [inline]
       __do_sys_clock_adjtime+0x172/0x290 kernel/time/posix-timers.c:1174
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x490 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
       ----                    ----
  rlock(&clk->rwsem);
                               lock(&ptp->n_vclocks_mux);
                               lock(&clk->rwsem);
  lock(&ptp->n_vclocks_mux);

 *** DEADLOCK ***

1 lock held by syz.7.4518/28069:
 #0: ffff88802fdc2130 (&clk->rwsem){++++}-{4:4}, at: get_posix_clock kernel/time/posix-clock.c:25 [inline]
 #0: ffff88802fdc2130 (&clk->rwsem){++++}-{4:4}, at: get_clock_desc+0x125/0x240 kernel/time/posix-clock.c:209

stack backtrace:
CPU: 0 UID: 0 PID: 28069 Comm: syz.7.4518 Not tainted 6.17.0-rc1-syzkaller-00038-g0cc53520e68b #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2043
 check_noncircular+0x14c/0x170 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+0x12a6/0x1ce0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:598 [inline]
 __mutex_lock+0x193/0x10b0 kernel/locking/mutex.c:760
 ptp_vclock_in_use drivers/ptp/ptp_private.h:113 [inline]
 ptp_vclock_in_use drivers/ptp/ptp_private.h:99 [inline]
 ptp_clock_freerun drivers/ptp/ptp_private.h:130 [inline]
 ptp_clock_freerun drivers/ptp/ptp_private.h:125 [inline]
 ptp_clock_adjtime+0x527/0x760 drivers/ptp/ptp_clock.c:125
 pc_clock_adjtime+0x115/0x1e0 kernel/time/posix-clock.c:239
 do_clock_adjtime kernel/time/posix-timers.c:1162 [inline]
 __do_sys_clock_adjtime+0x172/0x290 kernel/time/posix-timers.c:1174
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f58d7f8ebe9
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:00007f58d8dd0038 EFLAGS: 00000246 ORIG_RAX: 0000000000000131
RAX: ffffffffffffffda RBX: 00007f58d81b5fa0 RCX: 00007f58d7f8ebe9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: fffffffffffffffb
RBP: 00007f58d8011e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f58d81b6038 R14: 00007f58d81b5fa0 R15: 00007fff538b4688
 </TASK>