Hi,
n_gsm seems to lockup when I do following actions.
1) open n_gsm on tty
2) open /dev/ttygsm1 and keep it open
4) close n_gsm
Now I get following warning from lockdep. tty_vhangup() in n_gsm.c is
trying to acquire BTM while tty_set_ldisc is already holding it.
Inserting tty_unlock()/tty_lock() pair around tty_vhangup "solves" the
lockup problem, but still leaves lockdep warning for
lock(&tty->ldisc_mutex) and lock(big_tty_mutex) in SMP case.
Any ideas how to fix this for real?
=============================================
[ INFO: possible recursive locking detected ]
3.3.0-rc1-2-generic+ #51 Not tainted
---------------------------------------------
n_gsm_test/891 is trying to acquire lock:
(big_tty_mutex){+.+.+.}, at: [<c1497a74>] tty_lock+0x14/0x20
but task is already holding lock:
(big_tty_mutex){+.+.+.}, at: [<c1497a74>] tty_lock+0x14/0x20
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(big_tty_mutex);
lock(big_tty_mutex);
*** DEADLOCK ***
May be due to missing lock nesting notation
2 locks held by n_gsm_test/891:
#0: (big_tty_mutex){+.+.+.}, at: [<c1497a74>] tty_lock+0x14/0x20
#1: (&tty->ldisc_mutex){+.+.+.}, at: [<c1279ea3>]
tty_set_ldisc+0x173/0x2b0
stack backtrace:
Pid: 891, comm: n_gsm_test Not tainted 3.3.0-rc1-2-generic+ #51
Call Trace:
[<c1488e16>] ? printk+0x1d/0x1f
[<c10763ea>] print_deadlock_bug+0xda/0xe0
[<c1077ab2>] validate_chain.isra.35+0x5d2/0x6b0
[<c107977b>] __lock_acquire+0x34b/0x810
[<c107b7d0>] lock_acquire+0x90/0x1c0
[<c1497a74>] ? tty_lock+0x14/0x20
[<c10607d5>] ? local_clock+0x65/0x70
[<c149457d>] mutex_lock_nested+0x6d/0x340
[<c1497a74>] ? tty_lock+0x14/0x20
[<c127270d>] ? __tty_hangup+0x4d/0x3d0
[<c1497a74>] ? tty_lock+0x14/0x20
[<c1497a74>] tty_lock+0x14/0x20
[<c1272712>] __tty_hangup+0x52/0x3d0
[<c10784bb>] ? trace_hardirqs_on+0xb/0x10
[<c1272abd>] tty_vhangup+0xd/0x10
[<c127f514>] gsm_cleanup_mux+0xd4/0x1d0
[<c104e200>] ? abort_exclusive_wait+0x80/0x80
[<c127fbc2>] gsmld_close+0x42/0x80
[<c1279905>] tty_ldisc_close.isra.5+0x35/0x50
[<c1279ec6>] tty_set_ldisc+0x196/0x2b0
[<c10da815>] ? might_fault+0x95/0xa0
[<c1274d5a>] tty_ioctl+0x65a/0x7c0
[<c112b032>] ? fsnotify+0x252/0x680
[<c112ae56>] ? fsnotify+0x76/0x680
[<c1279c9d>] ? tty_ldisc_deref+0xd/0x10
[<c127203f>] ? tty_write+0x17f/0x230
[<c1077e42>] ? check_flags+0x12/0x20
[<c1274700>] ? no_tty+0x30/0x30
[<c11029a9>] do_vfs_ioctl+0x79/0x300
[<c1498415>] ? sysenter_exit+0xf/0x1a
[<c1102c62>] sys_ioctl+0x32/0x60
[<c14983dc>] sysenter_do_call+0x12/0x3c
--
Ville
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