TTY/n_gsm: Removing the wrong tty_unlock/lock() in gsm_dlci_release()
Commit 4d9b109060f690f5c835(tty: Prevent deadlock in n_gsm driver)
tried to close all the virtual ports synchronously before closing the
phycial ports, so the tty_vhangup() is used.
But the tty_unlock/lock() is wrong:
tty_release
tty_ldisc_release
tty_lock_pair(tty, o_tty) < == Here the tty is for physical port
tty_ldisc_kill
gsmld_close
gsm_cleanup_mux
gsm_dlci_release
tty = tty_port_tty_get(&dlci->port)
< == Here the tty(s) are for virtual port
They are different ttys, so before tty_vhangup(virtual tty), do not need
to call the tty_unlock(virtual tty) at all which causes unbalanced unlock
warning.
When enabling mutex debugging option, we will hit the below warning also:
[ 99.276903] =====================================
[ 99.282172] [ BUG: bad unlock balance detected! ]
[ 99.287442] 3.10.20-261976-gaec5ba0 #44 Tainted: G O
[ 99.293972] -------------------------------------
[ 99.299240] mmgr/152 is trying to release lock (&tty->legacy_mutex) at:
[ 99.306693] [<c1b2dcad>] mutex_unlock+0xd/0x10
[ 99.311669] but there are no more locks to release!
[ 99.317131]
[ 99.317131] other info that might help us debug this:
[ 99.324440] 3 locks held by mmgr/152:
[ 99.328542] #0: (&tty->legacy_mutex/1){......}, at: [<c1b30ab0>] tty_lock_nested+0x40/0x90
[ 99.338116] #1: (&tty->ldisc_mutex){......}, at: [<c15dbd02>] tty_ldisc_kill+0x22/0xd0
[ 99.347284] #2: (&gsm->mutex){......}, at: [<c15e3d83>] gsm_cleanup_mux+0x73/0x170
[ 99.356060]
[ 99.356060] stack backtrace:
[ 99.360932] CPU: 0 PID: 152 Comm: mmgr Tainted: G O 3.10.20-261976-gaec5ba0 #44
[ 99.370086] ef4a4de0 ef4a4de0 ef4c1d98 c1b27b91 ef4c1db8 c1292655 c1dd10f5 c1b2dcad
[ 99.378921] c1b2dcad ef4a4de0 ef4a528c ffffffff ef4c1dfc c12930dd 00000246 00000000
[ 99.387754] 00000000 00000000 c15e1926 00000000 00000001 ddfa7530 00000003 c1b2dcad
[ 99.396588] Call Trace:
[ 99.399326] [<c1b27b91>] dump_stack+0x16/0x18
[ 99.404307] [<c1292655>] print_unlock_imbalance_bug+0xe5/0xf0
[ 99.410840] [<c1b2dcad>] ? mutex_unlock+0xd/0x10
[ 99.416110] [<c1b2dcad>] ? mutex_unlock+0xd/0x10
[ 99.421382] [<c12930dd>] lock_release_non_nested+0x1cd/0x210
[ 99.427818] [<c15e1926>] ? gsm_destroy_network+0x36/0x130
[ 99.433964] [<c1b2dcad>] ? mutex_unlock+0xd/0x10
[ 99.439235] [<c12931a2>] lock_release+0x82/0x1c0
[ 99.444505] [<c1b2dcad>] ? mutex_unlock+0xd/0x10
[ 99.449776] [<c1b2dcad>] ? mutex_unlock+0xd/0x10
[ 99.455047] [<c1b2dc2f>] __mutex_unlock_slowpath+0x5f/0xd0
[ 99.461288] [<c1b2dcad>] mutex_unlock+0xd/0x10
[ 99.466365] [<c1b30bb1>] tty_unlock+0x21/0x50
[ 99.471345] [<c15e3dd1>] gsm_cleanup_mux+0xc1/0x170
[ 99.476906] [<c15e44d2>] gsmld_close+0x52/0x90
[ 99.481983] [<c15db905>] tty_ldisc_close.isra.1+0x35/0x50
[ 99.488127] [<c15dbd0c>] tty_ldisc_kill+0x2c/0xd0
[ 99.493494] [<c15dc7af>] tty_ldisc_release+0x2f/0x50
[ 99.499152] [<c15d572c>] tty_release+0x37c/0x4b0
[ 99.504424] [<c1b2dcad>] ? mutex_unlock+0xd/0x10
[ 99.509695] [<c1b2dcad>] ? mutex_unlock+0xd/0x10
[ 99.514967] [<c1372f6e>] ? eventpoll_release_file+0x7e/0x90
[ 99.521307] [<c1335849>] __fput+0xd9/0x200
[ 99.525996] [<c133597d>] ____fput+0xd/0x10
[ 99.530685] [<c125c731>] task_work_run+0x81/0xb0
[ 99.535957] [<c12019e9>] do_notify_resume+0x49/0x70
[ 99.541520] [<c1b30dc4>] work_notifysig+0x29/0x31
[ 99.546897] ------------[ cut here ]------------
So here we can call tty_vhangup() directly which is for virtual port.
Reviewed-by: Chao Bi <chao.bi@intel.com>
Signed-off-by: Liu, Chuansheng <chuansheng.liu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index b94737b..f34461c 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1705,11 +1705,8 @@
gsm_destroy_network(dlci);
mutex_unlock(&dlci->mutex);
- /* tty_vhangup needs the tty_lock, so unlock and
- relock after doing the hangup. */
- tty_unlock(tty);
tty_vhangup(tty);
- tty_lock(tty);
+
tty_port_tty_set(&dlci->port, NULL);
tty_kref_put(tty);
}