Re: [PATCH] tty: annotate tty_lock() for lockdep

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

Hi Jiri, 



> =============================================
> [ INFO: possible recursive locking detected ]
> 3.4.0-08218-gb48b2c3 #7 Not tainted
> ---------------------------------------------
> blogd/279 is trying to acquire lock:
>  (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff8150f51e>] tty_lock+0x3e/0x90
> 
> but task is already holding lock:
>  (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff8150f51e>] tty_lock+0x3e/0x90
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(&tty->legacy_mutex);
>   lock(&tty->legacy_mutex);
> 
>  *** DEADLOCK ***
> 

I saw a similar problem and applied your patch, but that doesnt seem to
help me.

INFO: possible recursive locking detected ]
3.4.0-uprobes-debug+ #86 Not tainted
---------------------------------------------
plymouthd/710 is trying to acquire lock:
 (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff813b5054>] tty_lock+0x6c/0x70

but task is already holding lock:
 (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff813b5054>] tty_lock+0x6c/0x70

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

       CPU0
       ----
  lock(&tty->legacy_mutex);
  lock(&tty->legacy_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by plymouthd/710:
 #0:  (tty_mutex){+.+.+.}, at: [<ffffffff8123f452>] tty_release+0x25a/0x536
 #1:  (&tty->legacy_mutex){+.+.+.}, at: [<ffffffff813b5054>]
tty_lock+0x6c/0x70

stack backtrace:
Pid: 710, comm: plymouthd Not tainted 3.4.0-uprobes-debug+ #86
Call Trace:
 [<ffffffff810346a6>] ? vprintk_emit+0x48e/0x4c8
 [<ffffffff8107847d>] validate_chain+0x6c7/0xe57
 [<ffffffff8106175e>] ? local_clock+0x41/0x5a
 [<ffffffff81074c71>] ? trace_hardirqs_off_caller+0x1f/0x9e
 [<ffffffff81079444>] __lock_acquire+0x837/0x8a8
 [<ffffffff810795b7>] lock_acquire+0x102/0x12f
 [<ffffffff813b5054>] ? tty_lock+0x6c/0x70
 [<ffffffff813b25b3>] ? mutex_lock_nested+0x2ee/0x320
 [<ffffffff813b5054>] ? tty_lock+0x6c/0x70
 [<ffffffff813b233a>] mutex_lock_nested+0x75/0x320
 [<ffffffff813b5054>] ? tty_lock+0x6c/0x70
 [<ffffffff81076116>] ? trace_hardirqs_on_caller+0x12f/0x166
 [<ffffffff813b5054>] tty_lock+0x6c/0x70
 [<ffffffff813b5093>] tty_lock_pair+0x3b/0x40
 [<ffffffff8123f45d>] tty_release+0x265/0x536
 [<ffffffff8110eaee>] fput+0x127/0x282
 [<ffffffff8123eb11>] tty_ioctl+0x3d6/0xa89
 [<ffffffff8110579a>] ? kmem_cache_free+0x1db/0x242
 [<ffffffff8111d0f6>] do_vfs_ioctl+0x466/0x4ac
 [<ffffffff813b4f51>] ? _raw_spin_unlock+0x2b/0x3f
 [<ffffffff813bc115>] ? sysret_check+0x22/0x5d
 [<ffffffff8111d192>] sys_ioctl+0x56/0x79
 [<ffffffff813bc0e9>] system_call_fastpath+0x16/0x1b