Messages in this thread | | | Date | Thu, 25 Jul 2019 13:26:51 +0200 | From | Greg Kroah-Hartman <> | Subject | Re: [BUG] n_gsm: possible recursive locking detected |
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On Wed, Jul 17, 2019 at 11:40:02AM +0200, Martin Hundebøll wrote: > Hi, > > The GSM0710 line discipline driver triggers a lockdep warning when disabling > the ldisc while holding a multiplexed virtual tty open: > > ============================================ > WARNING: possible recursive locking detected > 5.2.0-00114-gdab52e30156b #6 Not tainted > -------------------------------------------- > cmux/263 is trying to acquire lock: > e1e23b18 (&tty->legacy_mutex){+.+.}, at: __tty_hangup.part.0+0x58/0x27c > > but task is already holding lock: > d6eddf48 (&tty->legacy_mutex){+.+.}, at: tty_set_ldisc+0x3c/0x1bc > > 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 > > 3 locks held by cmux/263: > #0: d6eddf48 (&tty->legacy_mutex){+.+.}, at: tty_set_ldisc+0x3c/0x1bc > #1: f28bead9 (&tty->ldisc_sem){++++}, at: tty_ldisc_lock+0x50/0x74 > #2: e5d20e4f (&gsm->mutex){+.+.}, at: gsm_cleanup_mux+0x9c/0x15c > > stack backtrace: > CPU: 0 PID: 263 Comm: cmux Not tainted 5.2.0-00114-gdab52e30156b #6 > Hardware name: Freescale i.MX6 Ultralite (Device Tree) > [<c011184c>] (unwind_backtrace) from [<c010cc74>] (show_stack+0x10/0x14) > [<c010cc74>] (show_stack) from [<c0852488>] (dump_stack+0xd4/0x108) > [<c0852488>] (dump_stack) from [<c017be90>] (__lock_acquire+0x6ec/0x1e84) > [<c017be90>] (__lock_acquire) from [<c017ddc4>] (lock_acquire+0xcc/0x204) > [<c017ddc4>] (lock_acquire) from [<c086e9d0>] (__mutex_lock+0x64/0x90c) > [<c086e9d0>] (__mutex_lock) from [<c086f294>] (mutex_lock_nested+0x1c/0x24) > [<c086f294>] (mutex_lock_nested) from [<c04c02fc>] > (__tty_hangup.part.0+0x58/0x27c) > [<c04c02fc>] (__tty_hangup.part.0) from [<c04ce718>] > (gsm_cleanup_mux+0xe8/0x15c) > [<c04ce718>] (gsm_cleanup_mux) from [<c04ce7d4>] (gsmld_close+0x48/0x90) > [<c04ce7d4>] (gsmld_close) from [<c04c7e24>] (tty_set_ldisc+0xb8/0x1bc) > [<c04c7e24>] (tty_set_ldisc) from [<c04c0b70>] (tty_ioctl+0x640/0xcb0) > [<c04c0b70>] (tty_ioctl) from [<c0297e68>] (do_vfs_ioctl+0x41c/0xa5c) > [<c0297e68>] (do_vfs_ioctl) from [<c02984dc>] (ksys_ioctl+0x34/0x60) > [<c02984dc>] (ksys_ioctl) from [<c0101000>] (ret_fast_syscall+0x0/0x28) > Exception stack(0xc8ce1fa8 to 0xc8ce1ff0) > 1fa0: 00438000 00000000 00000003 00005423 beb6cc04 > beb6cc04 > 1fc0: 00438000 00000000 00000000 00000036 00000000 00000000 00438000 > beb6ccd4 > 1fe0: 00438048 beb6cbfc 00427684 b6f58b88 > > > Steps to reproduce using the attached cmux util: > > root@iwg26:~# ./cmux & > [1] 254 > SERIAL_PORT = /dev/ttymxc0 > AT+IFC=2: Ie5 +CFUN: 1 +CPIN: READY Call Ready AT+IFC=2,2 OK > AT+GMM : AT+GMM Quectel_M95 OK > AT : AT OK > AT+IPR=1: AT+IPR=115200&w OK > AT+CMUX=: AT+CMUX=0,0,5,512,10,3,30,10,2 OK > Line dicipline set > > root@iwg26:~# cat /dev/gsmtty1 & > [2] 262 > root@iwg26:~# kill %1 > [ 74.517449] ============================================ > [ 74.522769] WARNING: possible recursive locking detected > [ 74.528094] 5.2.0-00114-gdab52e30156b #6 Not tainted > [ 74.533065] -------------------------------------------- > <...> > > > This has supposedly been fixed before in 4d9b109060f6 ("tty: Prevent > deadlock in n_gsm driver"), but the fix was undone in be7065725590 > ("TTY/n_gsm: Removing the wrong tty_unlock/lock() in gsm_dlci_release()")
Do you have a patch that can resolve this given you have a test case?
thanks,
greg k-h
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