Messages in this thread | | | Subject | Re: [BUG] n_gsm: possible recursive locking detected | From | Martin Hundebøll <> | Date | Mon, 12 Aug 2019 22:59:36 +0200 |
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On 25/07/2019 13.26, Greg Kroah-Hartman wrote: > 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?
No, sorry.
I can try to cook a patch, but chances are I will break locking for someone else. Hints are welcome.
// Martin
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