[linux next] tty/pty: possible circular locking dependency detected

[Sergey Senozhatsky]

5.1.0-rc2-next-20190329

[    8.168722] ======================================================
[    8.168723] WARNING: possible circular locking dependency detected
[    8.168724] 5.1.0-rc2-next-20190329-dbg-00014-g4d25d68aaf88-dirty #3228 Not tainted
[    8.168725] ------------------------------------------------------
[    8.168726] bash/380 is trying to acquire lock:
[    8.168727] 00000000acce3dce (tty_mutex){+.+.}, at: pty_write+0x31/0xd0
[    8.168730] 
               but task is already holding lock:
[    8.168731] 00000000c4f3448a (&ldata->output_lock){+.+.}, at: n_tty_write+0x1b9/0x4a0
[    8.168733] 
               which lock already depends on the new lock.

[    8.168733] 
               the existing dependency chain (in reverse order) is:
[    8.168734] 
               -> #4 (&ldata->output_lock){+.+.}:
[    8.168737]        __mutex_lock+0x7e/0x8c0
[    8.168738]        n_tty_write+0x1b9/0x4a0
[    8.168739]        tty_write+0x192/0x2a0
[    8.168741]        vfs_write+0xb8/0x1a0
[    8.168742]        ksys_write+0x45/0xb0
[    8.168744]        do_syscall_64+0x59/0x3bb
[    8.168746]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
[    8.168746] 
               -> #3 (&tty->termios_rwsem){++++}:
[    8.168748]        down_write+0x38/0x70
[    8.168749]        tty_unthrottle+0x19/0x60
[    8.168750]        n_tty_open+0x86/0xa0
[    8.168751]        tty_ldisc_open.isra.0+0x2b/0x40
[    8.168752]        tty_ldisc_setup+0x1e/0x60
[    8.168753]        tty_init_dev+0xd9/0x1c0
[    8.168754]        tty_open+0x300/0x3c0
[    8.168756]        chrdev_open+0x97/0x1c0
[    8.168757]        do_dentry_open+0x12f/0x370
[    8.168758]        path_openat+0x2ce/0xaa0
[    8.168759]        do_filp_open+0x7e/0xd0
[    8.168760]        do_sys_open+0x15d/0x210
[    8.168762]        kernel_init_freeable+0x2ae/0x317
[    8.168764]        kernel_init+0xa/0x101
[    8.168765]        ret_from_fork+0x3a/0x50
[    8.168765] 
               -> #2 (&tty->ldisc_sem){++++}:
[    8.168767]        __ldsem_down_write_nested+0x55/0x280
[    8.168768]        tty_ldisc_lock+0x4b/0x70
[    8.168770]        tty_init_dev+0x93/0x1c0
[    8.168771]        tty_open+0x300/0x3c0
[    8.168772]        chrdev_open+0x97/0x1c0
[    8.168773]        do_dentry_open+0x12f/0x370
[    8.168774]        path_openat+0x2ce/0xaa0
[    8.168775]        do_filp_open+0x7e/0xd0
[    8.168776]        do_sys_open+0x15d/0x210
[    8.168777]        kernel_init_freeable+0x2ae/0x317
[    8.168778]        kernel_init+0xa/0x101
[    8.168779]        ret_from_fork+0x3a/0x50
[    8.168780] 
               -> #1 (&tty->legacy_mutex){+.+.}:
[    8.168781]        __mutex_lock+0x7e/0x8c0
[    8.168782]        tty_init_dev+0x50/0x1c0
[    8.168784]        tty_open+0x300/0x3c0
[    8.168785]        chrdev_open+0x97/0x1c0
[    8.168786]        do_dentry_open+0x12f/0x370
[    8.168787]        path_openat+0x2ce/0xaa0
[    8.168788]        do_filp_open+0x7e/0xd0
[    8.168789]        do_sys_open+0x15d/0x210
[    8.168790]        kernel_init_freeable+0x2ae/0x317
[    8.168791]        kernel_init+0xa/0x101
[    8.168792]        ret_from_fork+0x3a/0x50
[    8.168793] 
               -> #0 (tty_mutex){+.+.}:
[    8.168794]        lock_acquire+0x9a/0x170
[    8.168795]        __mutex_lock+0x7e/0x8c0
[    8.168796]        pty_write+0x31/0xd0
[    8.168797]        n_tty_write+0x130/0x4a0
[    8.168798]        tty_write+0x192/0x2a0
[    8.168800]        vfs_write+0xb8/0x1a0
[    8.168801]        ksys_write+0x45/0xb0
[    8.168802]        do_syscall_64+0x59/0x3bb
[    8.168803]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
[    8.168804] 
               other info that might help us debug this:

[    8.168804] Chain exists of:
                 tty_mutex --> &tty->termios_rwsem --> &ldata->output_lock

[    8.168806]  Possible unsafe locking scenario:

[    8.168806]        CPU0                    CPU1
[    8.168807]        ----                    ----
[    8.168807]   lock(&ldata->output_lock);
[    8.168808]                                lock(&tty->termios_rwsem);
[    8.168809]                                lock(&ldata->output_lock);
[    8.168810]   lock(tty_mutex);
[    8.168810] 
                *** DEADLOCK ***

[    8.168811] 4 locks held by bash/380:
[    8.168812]  #0: 0000000022cdab25 (&tty->ldisc_sem){++++}, at: tty_ldisc_ref_wait+0x24/0x50
[    8.168814]  #1: 00000000033fee14 (&tty->atomic_write_lock){+.+.}, at: tty_write_lock+0x18/0x50
[    8.168815]  #2: 00000000135c3a23 (&o_tty->termios_rwsem/1){++++}, at: n_tty_write+0x8c/0x4a0
[    8.168817]  #3: 00000000c4f3448a (&ldata->output_lock){+.+.}, at: n_tty_write+0x1b9/0x4a0
[    8.168819] 
               stack backtrace:
[    8.168820] CPU: 1 PID: 380 Comm: bash Not tainted 5.1.0-rc2-next-20190329-dbg-00014-g4d25d68aaf88-dirty #3228
[    8.168821] Call Trace:
[    8.168823]  dump_stack+0x67/0x90
[    8.168825]  print_circular_bug.isra.0.cold+0x1c5/0x225
[    8.168826]  check_prev_add.constprop.0+0x5f5/0xd20
[    8.168828]  ? mutex_destroy+0x50/0x50
[    8.168829]  __lock_acquire+0xc28/0xf90
[    8.168830]  ? __lock_acquire+0xc28/0xf90
[    8.168831]  lock_acquire+0x9a/0x170
[    8.168833]  ? pty_write+0x31/0xd0
[    8.168834]  ? pty_write+0x31/0xd0
[    8.168835]  __mutex_lock+0x7e/0x8c0
[    8.168836]  ? pty_write+0x31/0xd0
[    8.168837]  ? n_tty_write+0x1b9/0x4a0
[    8.168838]  ? __mutex_lock+0x7e/0x8c0
[    8.168839]  ? pty_write+0x31/0xd0
[    8.168840]  ? n_tty_write+0x1b9/0x4a0
[    8.168842]  ? pty_write+0x31/0xd0
[    8.168843]  pty_write+0x31/0xd0
[    8.168844]  n_tty_write+0x130/0x4a0
[    8.168845]  ? wait_woken+0xa0/0xa0
[    8.168846]  tty_write+0x192/0x2a0
[    8.168847]  ? n_tty_open+0xa0/0xa0
[    8.168849]  vfs_write+0xb8/0x1a0
[    8.168850]  ksys_write+0x45/0xb0
[    8.168851]  do_syscall_64+0x59/0x3bb
[    8.168852]  ? trace_hardirqs_off_thunk+0x1a/0x1c
[    8.168854]  entry_SYSCALL_64_after_hwframe+0x49/0xbe

	-ss