syzbot

ptp ptp0: delete virtual clock ptp4
======================================================
WARNING: possible circular locking dependency detected
6.17.0-rc1-syzkaller-00036-gdfc0f6373094 #0 Tainted: G     U             
------------------------------------------------------
syz.3.3108/26039 is trying to acquire lock:
ffff888076900130 (&clk->rwsem){++++}-{4:4}, at: posix_clock_unregister+0x4d/0xd0 kernel/time/posix-clock.c:184

but task is already holding lock:
ffff88814c1c6870 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at: n_vclocks_store+0xf1/0x6d0 drivers/ptp/ptp_sysfs.c:215

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&ptp->n_vclocks_mux){+.+.}-{4:4}:
       __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

-> #0 (&clk->rwsem){++++}-{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
       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

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

5 locks held by syz.3.3108/26039:
 #0: ffff88801f370b78 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2a2/0x370 fs/file.c:1232
 #1: ffff88807d134428 (sb_writers#7){.+.+}-{0:0}, at: ksys_write+0x12a/0x250 fs/read_write.c:738
 #2: ffff8880300eac88 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x28f/0x510 fs/kernfs/file.c:325
 #3: ffff88814c582d28 (kn->active#248){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x2b2/0x510 fs/kernfs/file.c:326
 #4: ffff88814c1c6870 (&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: 26039 Comm: syz.3.3108 Tainted: G     U              6.17.0-rc1-syzkaller-00036-gdfc0f6373094 #0 PREEMPT(full) 
Tainted: [U]=USER
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
 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
RIP: 0033:0x7f977ab8ebe9
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:00007f977b985038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f977adb6180 RCX: 00007f977ab8ebe9
RDX: 0000000000080001 RSI: 00002000000003c0 RDI: 0000000000000005
RBP: 00007f977ac11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f977adb6218 R14: 00007f977adb6180 R15: 00007ffd93b81058
 </TASK>
ptp ptp0: delete virtual clock ptp3
ptp ptp0: delete virtual clock ptp2
ptp ptp0: only physical clock in use now